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(Chest. 2005;128:370-381.)
© 2005 American College of Chest Physicians

Lung Cancer in Women*

Emerging Differences in Epidemiology, Biology, and Therapy

Leno Thomas, MD; L. Austin Doyle, MD and Martin J. Edelman, MD

* From the University of Maryland Greenebaum Cancer Center, Baltimore, MD.

Correspondence to: Martin J. Edelman, MD, University of Maryland Greenebaum Cancer Center, 22 South Greene St, Baltimore, MD 21201; e-mail: medelman{at}umm.edu


   Abstract
TOP
 Abstract
Introduction
 Risk Factors
 Pathobiology
 Molecular Abnormalities
 Therapeutic Implications
 Other Issues
 Conclusion and Outlook
 References
 
Lung cancer is the major cause of cancer-related death in both men and women in the United States. Emerging evidence indicates that there are differences in the pathogenesis and possibly increased susceptibility to lung cancer in women. In addition, considerable data support small, but important differences favoring women in terms of response to therapy and long-term survival after the diagnosis of lung cancer, regardless of histology or stage. These differences in both biology and outcome will be important considerations in the design of future trials of screening and therapy for lung cancer.

Key Words: DNA repair • estrogen receptor • human papilloma virus • non-small cell lung cancer • sex • small cell lung cancer


   Introduction
TOP
 Abstract
 Introduction
Risk Factors
 Pathobiology
 Molecular Abnormalities
 Therapeutic Implications
 Other Issues
 Conclusion and Outlook
 References
 
Lung cancer is now the leading cause of cancer mortality in both men and women in the United States. It is estimated that in 2004 lung cancer incidence will reach 173,700, accounting for 13% of all new cancer cases and 29% of cancer deaths.1 There has been a fourfold increase in lung cancer in women over the past 30 years (Fig 1 ), and it is estimated that this rise will not plateau until after 2010. This increase in lung cancer in women has been referred to as a "contemporary epidemic."2



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  		Figure 1. Lung cancer deaths in women. Reprinted with permission from Ahmedin et al.1

 
The rise in lung cancer-related mortality among women accompanied by a decrease among men has significantly altered the male/female ratio in this disease. While much of this altered epidemiology can be attributed to changing patterns of tobacco use, it is becoming increasingly apparent that the relative risks (RRs) of specific types of lung cancer, the relationship between smoking and lung cancer, as well as the response to therapy may not be the same for both sexes. There are several differences between lung cancer in men and women that are of growing importance and may impact on diagnosis, treatment, and outcome (Table 1 ).


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  		Table 1. Sex Differences in Lung Cancer

 

   Risk Factors
TOP
 Abstract
 Introduction
 Risk Factors
Pathobiology
 Molecular Abnormalities
 Therapeutic Implications
 Other Issues
 Conclusion and Outlook
 References
 
Smoking
Smoking is the overwhelming cause for lung cancer in both men and women; 85 to 90% of patients with lung cancer are current or former tobacco smokers. Smokers are 22 times more likely to die from lung cancer than nonsmokers.3 Although smoking is a risk factor for all histologic types of lung cancer, the association is stronger for small cell, squamous cell, and large cell carcinoma than for adenocarcinoma.

Women began smoking in significant numbers in the 1940s, with a peak incidence in the 1970s. Currently, 22% of women are smokers.4 While the death rate from smoking-related disease for men has leveled off, women’s rates continue to rise, both as a delayed effect of past smoking and a lower rate of smoking cessation. There is considerable controversy over the RR for lung cancer in women vs men at any given level of tobacco exposure. A hospital-based, prospective, case-control study by Zang and Wynder5 found that women had a 1.2- to 1.7-fold higher risk for lung cancer than men.5 CT screening of an at-risk population (ie, > 10 pack-years) yields an increased risk of lung cancer for women compared to men (odds ratio [OR], 2.7) after adjusting for age and smoking history.6 Bain et al,7 however, recently analyzed cohort data from the Nurses Health Study of women and the Health Professionals Follow-up Study of men and failed to find a difference in risk. In addition, they reviewed six other cohort studies that also failed to demonstrate a difference.7 At this time, the question remains unanswered. Despite this uncertainty regarding the RR of lung cancer between males and females, there is considerable evidence that the biology of the disease differs between the sexes.

Environmental Tobacco Smoke
Environmental tobacco smoke (ETS) accounts for approximately 3,000 lung cancer deaths each year in the United States among nonsmokers, primarily women. A nonsmoking woman has a 24% greater risk of lung cancer if she lives with a smoker.8 Urinary levels of nicotine, cotinine, 4-(methylnitrosamino)-1-(3-pyridyl)-butanol (NNK), a tobacco-specific carcinogen, and its glucuronide (NNAL-Gluc) were elevated in nonsmoking women exposed to ETS compared to those who were not exposed.9 A population-based, case-control study10 in central Florida among nonsmoking women demonstrated an elevated risk of lung cancer (or 2.4; 95% confidence interval [CI], 1.1 to 5.4) in women who were exposed to ≥ 22 years of ETS. Nonsmoking women with spouses who used tobacco had a 30% increased risk of lung cancer, with a higher risk in those women with increased levels of exposure in a multicenter case control study (p = 0.03).11

Family History
Patients with lung cancer have a higher number of relatives with lung cancer than control subjects.121314 The simplest explanation of this phenomenon is the clustering of cigarette smokers within families. While undoubtedly true, there is also an increased risk of lung cancer regardless of family smoking history. This finding suggests that genetic and perhaps other shared environmental factors may be present in this population.15 A US population-based, case-control study estimated the familial risk for lung cancer by restricting the analysis to nonsmokers.16 Cases were significantly more likely than controls to have a family history of aerodigestive cancers (OR, 2.78) and a trend toward an excess of lung cancer (OR, 4.14; p = 0.07). Previous studies for example in nonsmokers also demonstrated an increased risk in nonsmoking women, and this risk was found to be greater for adenocarcinoma of the lung.12,17 Schwartz et al12 demonstrated a similar trend in nonsmokers in general; in particular, the risk was found to be greater in women (ORs, 1.7 vs 0.5, respectively) than in men, and again adenocarcinoma was the predominant tissue type.

Diet
Other factors including diet pose a potential risk for the development of lung cancer. A prospective study18 examined the relationship between smoking, dietary antioxidants, and lung cancer risk. Women who consumed five or more carrots per week had an RR of 0.4 (95% CI, 0.2 to 0.8) compared with the risk for women who had not consumed carrots.18 Two prospective US cohorts lend further support to this observation.19 A 10-year follow-up of a cohort of men in the Health Professionals Follow-up Study and a 12-year follow-up period of a cohort of women in the Nurses Health Study found that new lung cancers were diagnosed in 275 of 46,924 men and 519 of 77,283 women. The risk of lung cancer was significantly reduced in those who had consumed a variety of carotenoids for a maximum protective period of 4 to 8 years even after adjusting for residual confounding from smoking (RR, 0.68; 95% CI, 0.49 to 0.94 for the highest compared with the lowest total carotenoid intake). Of note, the association was stronger in women than in men. Among female never-smokers, a significant 63% lower risk was noted.20

A hospital-based, case-control study demonstrated that fruit intake and the use of soy in Chinese women provided a protective effect against lung cancer.21 The same protective effect was observed with the consumption of green tea in a population-based, case-control study.22

Possible Association With Human Papilloma Virus Infection
Human papilloma virus (HPV) infection is a well-recognized event in the pathogenesis of cervical cancer. The most frequently implicated HPV viruses are types 6 and 11, which are associated with intraepithelial neoplasia, and types 16 and 18, which are associated with invasive cervical carcinoma. HPV DNA utilizing polymerase chain reaction (PCR) and in situ hybridization was detected in the tumors of 49% of women with lung cancer who also had a history of high-grade cervical intraepithelial neoplasia (grade III).23

A Taiwanese study24 revealed the presence of HPV DNA (types 16 and 18) in the cancer cells of nonsmoking women with lung cancer. Interestingly, HPV infection seems to be most associated with squamous lung cancer. Yousem et al25 demonstrated the occurrence of HPV 6/11, 16/18, and 31/33/35 serotypes in squamous metaplasia of the bronchus, but no association was found in adenocarcinoma or small cell carcinoma. Japanese studies2627 have detected HPV DNA (serotypes 6, 11, 16, and 18) in well-differentiated squamous cell carcinoma and in adenocarcinoma cells that were adjacent to squamous cell carcinoma.

There is far from universal agreement that HPV is an etiologic agent in lung cancer.282930 An analysis of paraffin-embedded tissue from 32 squamous bronchial carcinomas and 15 cervical cancers utilizing both in situ hybridization and PCR techniques was negative for HPV in the lung cancer cases, while 12 of the 15 cervical cases were positive.30 It is also quite possible that an association of HPV in lung cancer reflects the coexistence of increased and earlier smoking behavior with more frequent sexual contacts.


   Pathobiology
TOP
 Abstract
 Introduction
 Risk Factors
 Pathobiology
Molecular Abnormalities
 Therapeutic Implications
 Other Issues
 Conclusion and Outlook
 References
 
The development of lung cancer is the end result of a complex interplay of factors including carcinogen exposure, metabolism, and genetics. Tobacco smoke, recognized to be the foremost risk factor for lung cancer, contains more than a hundred diverse mutagens and carcinogens, including polycyclic aromatic hydrocarbons, N-nitro amines, and aromatic amines. The initiating activity remains for an extended period after the cessation of smoking.

Two classes of enzymes play a crucial role in the metabolism of tobacco-related carcinogens: the phase I and II detoxifying enzymes. While phase I enzymes (ie, cytochrome P450, monooxygenases) activate carcinogens to reactive intermediates, their action is balanced by phase II enzymes, which serve to convert these same reactive intermediates (ie, reactive oxygen species) to inactive conjugates that are more water soluble and hence excreted more readily. Polymorphisms have been found to alter the metabolic activity of detoxification enzymes. Those active metabolites that are not detoxified bind to DNA forming DNA adducts. Women have higher levels of these DNA adducts when compared to men.3132 The higher DNA adduct levels were also found to be associated with the expression of the cytochrome P4501A1 (CYP1A1) gene, an aryl hydrocarbon hydroxylase enzyme. This enhanced enzyme inducibility causes bioactivation of benzopyrene, a polycyclic aromatic hydrocarbon that is found in cigarette smoke.33 When noncancerous lung tissue from 159 patients with lung cancer was evaluated, both male and female smokers had much higher levels of DNA adducts compared with nonsmokers. Despite substantially fewer pack-years of smoking (22.9 vs 35.0, p = 9.4 x 10-5) and younger age (56.2 years vs 62.2 years, p = .034), women smokers had substantially higher levels of adducts (15.39 vs 12.08 per 108 DNA bases, p = 0.047). Increased adduct levels correlated with CYP1A1 levels, as measured by quantitative reverse transcriptase-PCR and normalized to the expression of GAPDH, which were substantially higher in female than male subjects (494 ± 334 CYP1A1 mRNA/106 GAPDH mRNA vs 210 ± 208, p = 0.016).32

Dresler et al34 confirmed the risk of high CYP1A1 expression to the development of lung cancer in women vs men (OR, 4.98 vs 1.37). In addition, the expression of the glutathione S-transferase M1 (GSTM1) gene was also evaluated. GSTM1 has the ability to inactivate highly reactive intermediates that are carcinogenic; hence, reduced expression of this gene could lead to an increased risk for smoking-related cancers including lung cancer.35 While nonexpression (null phenotype) did not increase risk by itself, a null phenotype combined with high CYP1A1 expression raised the risk ratio for lung cancer in women as opposed to men (OR, 6.54 vs 2.36), despite the fact that women in this study had a far less significant smoking history than men. The GSTM1 null phenotype was also associated with an increased risk of lung cancer in nonsmoking women with ETS. The OR was 2.6 for women with ETS exposure and GSTM1 null, compared to those expressing GSTM1. This risk increased with increasing exposure to ETS.36 It is important to be cautious in interpreting and generalizing these findings beyond the study populations given the wide ethnic and racial differences in hepatic enzyme phenotypes.37


   Molecular Abnormalities
TOP
 Abstract
 Introduction
 Risk Factors
 Pathobiology
 Molecular Abnormalities
Therapeutic Implications
 Other Issues
 Conclusion and Outlook
 References
 
Many genetic and epigenetic alterations of tumor suppressor genes have been demonstrated in lung cancer. The most frequent genetic alterations found are in p53 (in 90% of small cell lung cancers [SCLCs] 40 to 70% of non-small cell lung cancers [NSCLCs]) and in oncogenes such as K-ras. The p53 pathway has long been recognized as playing a key role in cell cycle regulation by causing arrest in both the G1 and G2 phases in cell division in response to DNA damage. This arrest allows for DNA repair or apoptosis. P53 mutation leads to abrogation of this arrest and perpetuation of DNA damage and consequent inhibition of the normal apoptotic mechanism. Smoking has been found to induce p53 mutation via the formation of DNA adducts. Women have been found to have higher levels of pulmonary DNA adducts per pack-year than men.38

Of the Ras family of proto-oncogenes, K-ras is the most frequently affected gene. As in the p53 gene mutation, the formation of DNA adducts secondary to the effects of smoking appears to play a pivotal role.39 Women are three times more likely to carry the K-ras mutation than men.4041 In most studies,4243 Ras mutations are predominantly associated with adenocarcinoma. Data regarding whether K-ras is an adverse prognostic variable are conflicting.44454647484950

Growth Factor Receptors
Certain growth factors have been shown to stimulate the growth of both normal and neoplastic cells in the lung. A receptor for the autocrine growth factor, gastrin releasing peptide receptor (GRPR), has been identified in both small cell lung cancer and NSCLC.5152 The GRPR gene is on the X chromosome and escapes X-inactivation. It is expressed more frequently in female nonsmokers (than male) and is activated earlier in response to tobacco exposure.53

ERBB2 (HER-2/neu) is one of four receptor-type tyrosine kinases that form a heterodimer with other members of the ERB-B class and mediates cell growth and survival. HER 2/neu has been found to be overexpressed in 25 to 30% of invasive breast cancers and is associated with a more aggressive clinical course. Its incidence in NSCLC varies from 27 to 63%.54 In advanced NSCLC, one study55 found inferior survival for patients with high serum levels of HER-2/neu compared to patients with lower levels (median, 7.1 months vs 10.9 months; p = 0.004). Previously, several surgical series5657 found that overexpression of HER-2/neu is associated with a poorer prognosis and survival. HER-2/neu is most commonly expressed in adenocarcinoma, the most common subtype in women.58 Despite these observations, treatment with trastuzamb (a monoclonal antibody to Her2/neu) in addition to standard chemotherapy failed to improve outcome.59

DNA Repair Capacity
An emerging literature implicates differences in DNA repair capacity (DRC) in both the pathogenesis of lung cancer and response to therapy. A complex family of proteins exists to remove damaged DNA segments or to repair mismatched nucleotides. Deficiencies in this process are unequivocally mutagenic and carcinogenic. Wei et al60 evaluated the repair of tobacco carcinogen-induced DNA adducts and lung cancer risk. Lymphocytes were obtained from newly diagnosed lung cancer patients (n = 316) or from age-, sex-, and smoking status-matched control subjects (n = 316). Cells were cultured and transfected with a plasmid containing a reporter gene that would not be expressed if the plasmid DNA was damaged. Lymphocytes were then exposed to the known tobacco-derived carcinogen, benzo(a)pyrene diolepoxide. Younger patients (< 60 years old), those with a family history of lung cancer, and female patients had a lower DRC and a higher lung cancer risk.60 These results were confirmed in a much larger case-control study with 764 lung cancer patients and 677 control subjects.61

Paradoxically, this relative deficiency in DRC may relate to the observation that women have better responses and survival when treated with platinum-based chemotherapy. Platinum agents act through the formation of DNA adducts resulting in cycle arrest and apoptosis. Repair of these adducts is one mechanism of resistance to platinum agents. Recent studies have demonstrated that diminished DRC (as a result of less ERCC1, a DNA repair enzyme) is associated with improved outcome in stage IV NSCLC treated with cisplatin-based chemotherapy.62

Hormonal Influences
The most obvious biological differences between the male and female are hormonal. An estrogen-driven environment is a recognized factor in the pathogenesis of breast, endometrial, and ovarian cancers. With the increasing rates of lung cancer in women and their increased susceptibility to the detrimental effects of tobacco smoke compared to men, the role of female steroid sex hormones has been hypothesized to be a factor in lung carcinogenesis. Estrogen receptors are abundantly expressed in normal lung tissue and in lung tumor cell lines at the messenger RNA level.63 Stabile64 has demonstrated that the most common estrogen receptor (ER) expressed in lung cancer is a variant of ER{alpha} (most likely as a result of alternative splicing) which contrasts to the abundant expression of the classic estrogen receptor, ER{alpha} in hormone sensitive breast cancers. The novel ER ERß was also expressed and was found to be a mixture of full-length and alternative splicing. ß-Estradiol has a proliferative effect on normal lung fibroblasts and lung cancer cell lines in vitro. There was a 17-fold increase in cellular proliferation in lung cancer-derived cell line as opposed to only a 3.8-fold increase when normal lung fibroblasts were incubated with ß-estradiol. This finding suggests an increased responsiveness of malignant clones to estrogen.

The exact role of estrogens in lung cancer is not clear, but they may act as direct carcinogens via the formation of DNA adducts.6566 Other mechanisms include a possible indirect role in the activation of several growth factor genes, such as transforming growth factor-{alpha}, epidermal growth factor, and insulin-like growth factor-1, all of which in turn have been known to mediate cell division in lung neoplasms.67

Previous data have been conflicting regarding the prognostic value of ER receptors. Expression of the ER-related protein p29 was inversely related to survival in women, whereas a positive trend was noted in men.68 Yang69 observed that the 5-year survival rates for ER-negative patients was higher than for ER-positive patients (72.5% vs 8.8%, respectively).

Hormone replacement therapy (HRT) in women is very controversial. Adami et al70 showed an increased risk (RR, 1.26) of lung cancer in women receiving HRT. Taioloi and Wynder71 showed that the use of HRT and its interaction with smoking leads to an increased risk of lung cancer in women (ORs, 1.7 and 32.4 in nonsmokers and smokers, respectively), while early menopause was associated with a decreased risk (OR, 0.3) of adenocarcinoma in women. It appears that the higher circulating levels of estrogen in women when compared to men, coupled with their lower rate of DNA repair, make women particularly susceptible to the carcinogenic influence of tobacco smoke. Soy phytoestrogens have been shown to compete with endogenous estradiol for ERs and have been shown to have a protective effect against lung cancer.72

There are data that HRT may actually exert a protective effect. A case-control study from Texas of 499 women with lung cancer and 519 age-, ethnicity-, and smoking-matched control subjects found that HRT was associated with a reduced risk of lung cancer in current smokers (OR, 0.59; 95% CI, 0.38 to 0.92). However, this reduced risk was not seen in never-smokers or former smokers.73

Moore et al74 analyzed the Surveillance, Epidemiology, and End Results Database to evaluate the influence of menopausal status on outcomes in lung cancer. Utilizing an average menopausal age of 51 years, they classified 14,676 women entered in the database into premenopausal and postmenopausal groups. In addition to comparisons between the two groups, there were also comparisons against men from similar age groups. Several intriguing differences emerged between the groups. Premenopausal women tended to present with more extensive disease and adenocarcinoma than postmenopausal women. They underwent more extensive surgical procedures (pneumonectomies, vs lobectomies) at every stage of disease (p < 0.0001) and were more likely to receive radiotherapy (58% vs 48%, p < 0.0001). While premenopausal women and younger men had similar mortality (after adjustments for covariates), postmenopausal women had fewer lung cancer-related deaths compared with older men.

The authors acknowledge that a major limitation of this study is the potentially confounding effects of age. However, the different death rates for postmenopausal women as opposed to older men seems to confirm a sex-specific effect.


   Therapeutic Implications
TOP
 Abstract
 Introduction
 Risk Factors
 Pathobiology
 Molecular Abnormalities
 Therapeutic Implications
Other Issues
 Conclusion and Outlook
 References
 
Although the incidence of lung cancer is higher in women than in men and continues to rise, women have superior responses to therapy. This appears to be true regardless of stage, therapeutic modality, or histology (Tables 2, 3 ). In the mid-1970s, Edmonson et al75 noted that "survival was better for ambulatory patients and women survived longer than men" regarding outcome of chemotherapy-treated patients with adenocarcinoma or inoperable small cell carcinoma of the lung. The Surveillance, Epidemiology, and End Results Database (31,226 patients) of lung cancer has been analyzed for prognostic factors and has identified the following as favorable prognostic factors: low-stage disease, surgical therapy, age < 50 years, and female sex.76 A Polish population-based study77 of 20,561 cases of lung cancer between 1995 to 1998 revealed that female patients had a better prognosis than males regardless of the modality of therapy, with an RR of death of 1, compared to 1.21 (p = 0.001) in male patients by univariate analysis. It was also noted in this series that women patients were younger (age < 50 years: 23.3% vs 12%, p < 0.001), and were more likely to have adenocarcinoma (21.6% vs 9.6%, p < 0.001) and SCLC (26.6% vs 19.9%, p < 0.001). More women were nonsmokers compared to men (18.8% vs 2.4%, p < 0.001). A multivariate analysis of absolute survival in this series showed that the RR of death was significantly higher for men (1.15; p = 0.001).


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  		Table 2. Treatment Results by Sex in NSCLC*

 

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  		Table 3. Treatment Results by Gender: SCLC

 
NSCLC
In localized (ie, stage I, II) NSCLC, women will experience superior survival after either surgical resection or radiation as single modalities. A Japanese study78 of resected NSCLC noted that women have a significantly longer survival rate than men (p = 0.0036), although on multivariate analysis the difference was significant only in stage III disease (p = 0.0234). Minami et al79 evaluated the results of 1,242 consecutive operative interventions for lung cancer and noted that complete resection was achieved less often in women than in men (79.6% vs 85.2%). However, women who underwent a complete resection survived longer (5-year and 10-year survival rates were 69% and 51%, respectively) than their male counterparts. Women < 60 years of age did not show a significantly longer survival than men, but women > 60 years old survived significantly longer.79

Ferguson et al80 evaluated the outcomes of 451 patients who underwent surgical resection for localized lung cancer between from 1980 to 1998 with an emphasis on sex-associated differences. There was an overall superiority in median survival favoring women vs men (41.8 months vs 26.9 months, respectively). This gender gap was particularly pronounced in stage I disease (109.8 months vs 50.3 months, p = 0.0008). However, in a Cox proportional hazards model, this advantage did not reach significance when other factors including age and FEV1 were considered.80

Female sex has also been associated with superior outcome in patients treated with radiotherapy as well. Werner-Wasik et al81 reviewed 1,999 patients treated in nine Radiation Therapy Oncology Group trials between 1983 and 1994 with thoracic radiation with or without chemotherapy (cisplatin-based). Women had a significantly better outcome than men, 11.4 months vs 9.9 months, respectively.

Female sex was also noted to be an independent positive prognostic factor after trimodality therapy (chemotherapy, radiotherapy, and surgery). The Southwest Oncology Group (SWOG)82 evaluated concurrent cisplatin/etoposide plus chest radiation followed by surgery for stages IIIA and IIIB NSCLC. A univariate analysis of prestudy factors revealed that the two best predictors of survival were substage and sex. The survival time for women was 21 months, vs 12 months for men (p = 0.08).

A similar survival advantage for women is present in advanced-disease patients treated with chemotherapy. Albain et al83 reviewed the 2,531 patients enrolled in 13 SWOG trials of therapeutic interventions in "extensive stage nonsmall cell lung cancer" conducted between 1974 and 1987. Female sex was a strong independently favorable factor for survival with a risk ratio of 0.77.83 The median survival ratio for females/males was 5.7/4.8, with 1-year survival rates of 19% vs 14% (p ≤ 0.01 for survival comparisons within each category). Almost identical results were noted by the European Lung Cancer Working Party (ELCWP) in a review of 1,052 patients with locally advanced or metastatic NSCLC treated with cisplatinum-based chemotherapy from 1980 to 1991.84 Among 23 pretreatment variables evaluated, female sex emerged as one of eight significantly associated with superior survival. An RR of 0.7 (p = 0.03) was noted in multivariate analysis. In an analysis of 378 by O’Connell et al,85 patients, Karnofsky performance scale > 80, normal lactate dehydrogenase (LDH) level, 0–1 nonosseous metastases, and female gender were noted to have improved overall survival.

A randomized trial of postoperative therapy by the Eastern Cooperative Oncology Group86 also shows a trend toward better outcomes for women compared to men (median survival of all men; 35 months; for women, 41 months; p = 0.12). Multivariate analyses demonstrated significantly improved survival for women with nonsquamous histology (p < 0.01).

Preliminary results of an analysis of 91 patients (21 female) with curatively resected NSCLC demonstrated that several prognostic markers appeared to be sex specific.87 High levels of ERCC1, Her2, and RXRß predicted for better survival in women, but not in men. In men, low cyclooxygenase-2 expression and high ornithine decarboxylase expression predicted for better survival, but were not predictive in women. This study is limited by its small numbers and will require validation. However, it serves to further emphasize the potential importance of gender in analyzing both outcomes results as well as potential predictive and prognostic markers.

SCLC
In SCLC, women similarly will experience superior outcomes. The NCI-Navy Medical Oncology Branch analyzed the results of four consecutive prospective trials and found that women had superior survival compared with men.88 This advantage was most pronounced for patients surviving > 2.5 years, implying that the chance of cure is higher in women than in men. This difference was independent of other factors analyzed.

The ELCWP analyzed 763 patients with a minimum follow-up of 5 years and demonstrated that female patients had a better objective response (80%, vs 69% for male) in a univariate analysis, but the comparison was not statistically significant (p = 0.16). In a multivariate analysis, women did better than men (OR, 1.82 for female patients; 95% CI, 1.00 to 3.34; p = 0.05). However, there were relatively few women (10%) analyzed in this series.89

A total of 2,580 patients enrolled on 10 SWOG SCLC trials including both limited disease (LD) and extensive-stage disease (ED) were analyzed for prognostic indicators. In the six SWOG LD trials, good performance status (0 to 1), age < 70 years, normal LDH level, and female sex (p = < 0.001 for all these variables; median survival in females, 24.4 months, vs 17.7 months in men) were significant favorable independent predictors and therefore predicted for the best outcome.90 In the SWOG ED trials,90 the most favorable prognostic factors were good performance status and normal LDH level. There was a nonsignificant trend toward superior survival in females.

Bronchiolalveolar Carcinoma
There is emerging evidence that bronchiolalveolar carcinoma (BAC) represents a distinct clinicopathologic entity. Though currently considered as a subset of adenocarcinoma (with the formal terminology of "adenocarcinoma with bronchioalveolar features"), there are clear differences. True BAC as defined by the World Health Organization/International Association for the Study of Lung Cancer is characterized by a lepidic growth pattern and lack of invasiveness and distant metastases.91 The actual diagnosis can only be made with a completely resected surgical specimen, and this has resulted in some confusion as most patients with advanced disease are diagnosed based on biopsy specimens. Biologically, it is characterized by a distinct pattern of gene expression.92 Clinically, there is relatively frequent occurrence in younger, female nonsmokers. The disease tends to progress more indolently than other NSCLC, though it also appears to be less sensitive to conventional platinum based therapies.93 Interestingly, BAC appears to be the subset of NSCLC with the greatest responsiveness to gefinitib or erlotinib, the tyrosine kinase inhibitor of epidermal growth factor receptor signaling. Two large phase II trials of gefitinib monotherapy, the IRESSA Dose Evaluation in Advanced Lung Cancer (IDEAL) 1 and IDEAL 2 studies9495 evaluated the agent in pretreated NSCLC. Retrospective subset analysis demonstrated that female sex, adenocarcinoma (in particular, bronchiolalveolar histology), and nonsmoking status were predictors of response.9596 In the IDEAL 2 study,95 50% of women experienced symptomatic response, vs 31% of men (p = 0.006). Radiographic regression was also seen in 19% of women, vs only 3% of men (p = 0.001). The results of these studies, both in terms of the activity of gefinitib in general as well as predictive factors of response, should be viewed with caution as neither trial was randomized and the factors analyzed were retrospectively selected. Similar results have been obtained with erlotinib, a chemically similar agent recently approved for the second- and third-line therapy of advanced NSCLC.97


   Other Issues
TOP
 Abstract
 Introduction
 Risk Factors
 Pathobiology
 Molecular Abnormalities
 Therapeutic Implications
 Other Issues
Conclusion and Outlook
 References
 
Smoking Cessation
Smoking is the most predominant risk factor for all the different tissue types of lung cancer. It has long been known that the risk of lung cancer declines after smoking cessation. The risk after a patient stops smoking appears to be related to the level of consumption. In those persons who have smoked 1 to 20 cigarettes per day, the risk decreases to 1.6 at 15 years after smoking cessation. In those who had smoked > 21 cigarettes per day, the risk for lung cancer at 15 years after quitting smoking remains fourfold that of a never-smoker. Among all previous smokers, there was a consistent decline in the combined ORs for all histologic types of lung cancer. In ex-smokers, women had a greater risk reduction for squamous cell and SCLC when compared to men.98 Between 1 year and 4 years of cessation, there was a 19% reduction in the risk of SCLC, and the lowest risk reduction (12%) was for adenocarcinoma. After > 10 years of smoking cessation, there was 65% risk reduction for SCLC, while the reduction in risk for adenocarcinoma was only 47%. Of note, in this study, it was noted that women had a greater reduction in the risk of SCLC and squamous cell cancer compared to men. With adenocarcinomas, however, this difference was not significant.


   Conclusion and Outlook
TOP
 Abstract
 Introduction
 Risk Factors
 Pathobiology
 Molecular Abnormalities
 Therapeutic Implications
 Other Issues
 Conclusion and Outlook
References
 
Lung cancer is the major cause of cancer-related death in women. It is possible that women are inherently more susceptible to lung cancer, although that issue is far from settled. There are, however, very clear differences in the biology, natural history, and response to therapy between men and women with this disease. An emerging literature provides a biological basis for these differences, but this understanding is quite tentative. Most of the literature on this topic is retrospective and subject to various biases. Prospective evaluations of these differences, particularly as they apply to clinical practice, are required. Furthermore, as new therapeutic interventions are evaluated, the potential for differential response based on sex must be prospectively considered in trial design. Studies or arms of randomized studies with imbalances in terms of sex may lead to false conclusions. Given the superior prognosis for women in most clinical trials, future studies should stratify for the variable of sex. For current clinical practice, there is only one clear area for which sex enters into the equation in patient management. The value of the epidermal growth factor receptor tyrosine kinase inhibitors (gefitinib, erlotinib) are clearly most pronounced in never-smoking females. The level of activity may warrant initial use of these agents in this group as opposed to standard therapy. However, even in this situation, this approach will require confirmation from prospective clinical trials. Tragically, for both men and women, this disease is largely preventable through smoking cessation.


   Footnotes
 
Abbreviations: BAC = bronchiolalveolar carcinoma; CI = confidence interval; DRC = DNA repair capacity; ED =extensive-stage disease; ELCWP = European Lung Cancer Working Party; ER = estrogen receptor; ETS =environmental tobacco smoke; HPV = human papilloma virus; HRT = hormone replacement therapy; IDEAL = IRESSA Dose Evaluation in Advanced Lung; LD = limited disease; NSCLC = non-small cell lung cancer; OR = odds ratio; PCR = polymerase chain reaction; RR = relative risk; SCLC = small cell lung cancer; SWOG = Southwest Oncology Group

Learning Objectives: 1. Identify major differences between men and women diagnosed with lung cancer as it relates to biological and natural history as this disease progresses. 2. State the different responses to the therapeutic interventions between men and women diagnosed with lung cancer.

Dr. Edelman has indicated to the ACCP that he has not received anything of value, either directly or indirectly, from a commercial or other party related directly or indirectly to the subject of this article submission.

Received for publication September 13, 2004. Accepted for publication January 10, 2005.


   References
TOP
 Abstract
 Introduction
 Risk Factors
 Pathobiology
 Molecular Abnormalities
 Therapeutic Implications
 Other Issues
 Conclusion and Outlook
 References
 

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