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* From the Cuneo Lung Cancer Study Group at the "S. Croce and Carle" General Hospital, Cuneo, Italy.
Correspondence to: Gianfranco Buccheri, MD, Divisione di Pneumologia, Ospedale "S. Croce e Carle," Cuneo I-12100, Italy; e-mail: buccheri{at}culcasg.org
| Abstract |
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Design: Analysis of a single institution database over a 16-year period from 1983 to 1998.
Setting: Community-based hospital and second referral level institution for a province of 500,000 people.
Patients: The study included 1,296 consecutive patients (1,117 men), with pathologically documented lung cancer (46% with squamous cell cancer), staged both clinically (77%) and pathologically (23%), and treated, for the most part, with chemotherapy (52%).
Interventions: Anthropometric, clinical, and laboratory data were recorded prospectively. Survival analysis was performed by the Kaplan-Meier method and Cox multivariate regression analysis.
Measurement and results: The 1997 revised ISSLC classification fit well with the cohort studied. Each stage and substage significantly differed from each other, except for stage IIA. In this stratum, there were only 13 patients. Comparing the 1986 and the 1997 classifications, no substantial differences were observed (log-rank statistics, 295 vs 293, respectively; p < 0.0001). Independent of the classification used, the Cox models were always highly predictive of the outcome. The only way to increase their efficiency was to replace the variable stage with the original TNM descriptors.
Conclusions: Since grouping different TNM subsets into one stage is not really helpful, we might choose to use TNM descriptors in clinical practice and in research.
Key Words: classification lung neoplasm multivariate analysis neoplasm staging non-small cell lung cancer prognosis
| Introduction |
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Starting from this premise, we undertook the current data analysis to respond to three main questions. The first question is how the 1997 staging system works when applied to an unselected population of lung cancer patients. Such patients are often inoperable at presentation and, thus, are clinically staged. About 20% of these patients may undergo an intervention, but the surgical exploration may not be as accurate as it was in the 5,319 patients who formed the basis for the new staging evaluation.6 To what extent can we generalize from the information that was validated in the surgical wards of highly qualified and hyperselective cancer centers? The second question is whether the new 1997 staging system has improved the overall prognostic capability, as compared with the 1986 classification. Apart from moving "satellite" tumor nodules found within the lobe of the primary tumor into the T4 category, the 1997 staging system regards almost exclusively a more complex grouping of the TNM descriptors.6 Survival rates may differ significantly between stages,9 but the overall improvement in prognostic capability of the new staging classification might be modest or even null. Finally, we were interested in exploring other ways of considering TNM descriptors that might ensure a better prognostic assessment.
| Materials and Methods |
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Statistical Analysis
Statistical analysis was performed using computer software (SPSS
for Windows, version 8.0; SPSS Inc; Chicago, IL). Survival curves were
generated with the Kaplan-Meier method 16
and were
compared by means of the log-rank test.17
Multivariate
survival analyses were made using the Cox regression model and were
stratified by tumor cell type.18
Survival times were
recorded from the time of the first visit for a suspected lung cancer
to death or to May 1999, when a check on the status of patients
believed to be alive was made. Since no reliable data about the causes
of deaths were available, all the deaths were attributed to cancer. All
statistical tests were two sided.
| Results |
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60) in 18% of them.
Nearly half of the 1,243 assessed patients complained of weight loss at
their first evaluation. CEA and tissue polypeptide antigen (TPA) tests
were performed in 1,136 and 1,115 patients, respectively (86 to 88% of
patients, respectively). Despite this partial data deficiency, we
decided to keep tumor markers in all multivariate models because of
their intrinsic prognostic value.10
11
The median TPA
serum level increased moderately, as would be expected for a mixed
population containing different prognostic strata.11
Univariate Analyses of Survival
At the time of the survival analysis, 1,063 patients had already
died, while 233 were still alive.
Figures 1 and 2 , complemented by Table 4 , show how well both the 1986 and 1997 stage classifications were able to discriminate between patients with similar prognoses. In addition, Table 4 shows the results of the same analysis limited to pathologically staged patients. Survival curves are displayed in logarithmic scale to emphasize differences between strata that would have been insufficiently appreciable otherwise.
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Differences between stages were highly significant (p < 0.0001) in both the 1986 and 1997 versions of the ISSLC. The log-rank statistics, which measure the equality of the survival distributions, were very similar between the 1986 and 1997 versions (ie, 295 and 293, respectively). Pairwise comparisons between adjacent stages were highly significant within the 1986 grouping (Fig 1) but were not always so significant in the 1997 version of the ISSCL (Fig 2) . For example, there were no differences between stages IB and IIA or between stages IIA and IIB, mainly due to the scarcity of patients in stage IIa (only 13 patients). Essentially, both stage groupings were highly and equally predictive. However, since the prognostic content of the 1997 grouping was split into more strata, each of them shared a lower prognostic capability.
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Multivariate Analyses of Survival
In a first run, the Cox proportional hazards regression analyses
included only stage groupings to verify further the similarity of their
prognostic significance (Table 5
). The overall
2 values were 281, 270, and 262,
respectively, for the 1986, 1997, and 1997-modified groupings.
Similarly, in the pathologically staged subgroup, the
2 values were 91, 85, and 87, respectively,
for each of the above groupings. All these values were highly
significant (p < 0.0001).
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An alternative approach for stage groupings would be the use of TNM
descriptors as they are, without grouping them into one derived
variable. This implies handling three variables rather than one, with
32 potential combinations rather than the 7 in the last version of the
ISSLC. However, the use of TNM descriptors would be simpler in clinical
practice because it would not require the grouping of descriptors into
one stage, and it could be even more helpful in clinical research,
providing more details on tumor extension. Actually, when we replaced
the stage of disease with the TNM descriptors, we found that the
overall
2 value increased to 422. This value
increased further when the number and the sites of metastases were
inserted into the equation (Table 5)
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Table 6 shows the model that best fit the data without excessively increasing the number of stage-related cofactors.
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| Discussion |
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We had the following three main purposes in planning this study: (1) to verify the validity of the last revision of the ISSLC in an unselected general population of lung cancer patients; (2) to compare the latest revision with the prior one; and (3) to explore the possibility of using better ways to accomplish the same objectives. We believe that our study has confirmed that the 1997 revision of the ISSLC is valid (with the possible exception of stage IIA) and generally applicable. Excluding perhaps the new biological factors,20 21 the stage of disease remains the best predictor of survival, 22 and this has been demonstrated once again. However, we saw no global improvement using the new staging classification, and, therefore, the answer to the second question we posed at the beginning of this article should be "no improvement." At least with respect to the prognosis, the new version of the ISSLC was no better than the previous one. Finally, our data have shown that, to improve our prognostic capability further, TNM factors should be used as they are, without grouping them into a stage of disease.
Many investigators have tested the new ISSLC by trying to fit their survival data,5 8 23 24 25 26 and many commentators already have discussed the merits and demerits of the introduced changes.2 3 4 8 9 27 Others have posed specific questions, including the opportunity of splitting stage I into two stages,5 moving T3N0M0 disease into stage IIB,5 25 assessing the role of satellite nodules,24 and reconsidering the need for a stage IIA.26 28
Inoue and colleagues 5 investigated the prognosis of 1,310 patients who underwent resection for NSCLC. These authors found significant differences in survival rates among patients with T1N0M0 and T2N0M0 tumors and no differences among patients with T2N1M0 and T3N0M0 tumors. They, like others,9 concluded that splitting stage I into stages IA and IA or putting T3N0M0 tumors into stage IIB was a sound decision. Mizushima and collaborators25 studied the appropriateness of the new ISSLC with special emphasis on the T3N0M0 tumor group.6 They analyzed 119 patients with NSCLC who had undergone pneumonectomy. Stage IIB included 14 patients with T3N0M0 tumors. In this group, the authors reported a 5-year survival rate of 69.6%, which was superior even to the 55.7% found in the T1N1M0 and T2N1M0 subsets. Mizushima et al25 also concluded that down-staging the T3N0M0 tumor group was appropriate. Our data are in fair agreement with these reports. In our group of nonsurgical patients, the division of stage I into stages IA and IB was capable of separating two strata with different prognoses. In addition, our patients with a T3N0M0 disease seemed to enjoy a relatively good outcome. In surgical patients, this was indirectly proved by the 91-week difference in median survival times that was observed between stages IIB and IIIA, from the new system, compared with the 32-week difference for stages II and IIIA, from the old system. However, TN status had to be confirmed pathologically, since, otherwise, the clinical underestimation of the real extent of disease hides (or even inverts) the effect. This is the reason why the above differences showed an opposite trend when all 1,296 patients were taken into account.
Yano and coworkers24 conducted a validation of the new ISSLC, concentrating on the inclusion of satellite nodes into the T4 category. They reviewed the clinical records of 352 patients with T2 to T4 resected lung cancers. No satellite nodules were found in 305 patients, one satellite nodule in the same lobe of the primary tumor was found in 39 patients, and a satellite nodule in another ipsilateral lobe was found in 8 patients. The authors reported no statistically significant differences in survival rates between patients without satellite nodules and patients with nodules within the ipsilateral primary lobe when the primary tumor was not advanced. For patients with tumors classified as T4, independent of the presence or absence of satellite nodules, the 5-year survival rate was 0% in the group without satellite nodes, 33.3% in the group with nodules within the primary lobe, and 0% in the group with nodules in nonprimary tumor lobes. The authors concluded that patients with satellite nodes in the primary tumor lobe might even elevate the survival rate of patients classified as having T4 tumors. We have no personal data to add, since we saw only four patients with pathologically documented satellite nodules of the primary ipsilateral tumor lobe and no other distant metastasis. According to our policy, they were soon reclassified as having T4M0 tumors. However, the debate clearly has scarce relevance for an unselected nonsurgical series.
However, the major limitation of the new ISSLC may be something different. In our cohort, there were very few patients classified as having T1N1M0 tumors or as having stage IIA disease, accounting for 13 (only 8 of whom had pathologic confirmation) of 1,296 patients (1% of the total population). Such low occurrence is the probable cause of the nonsignificant differences observed between the survival distributions of stages IIA and IB and of stages IIA and IIB. This observation is not new.26 28
There are multiple goals for the use of a cancer staging system. Using the words of Leong and colleagues,9 the goals are the following: (1) to standardize the description of disease; (2) to reflect prognosis; (3) to direct treatment; and (4) to facilitate research and the comparison of results. With this study, we have addressed the prognostic value of the refining of the ISSLC.6 We believe that the other purposes of a staging system are consequential, since the ability of a staging system to identify patients with similar prognoses is the premise for its use both in research and in clinical practice. A better characterization of the different prognostic strata was, indeed, the main objective of the revision of the ISSLC,6 which was pursued by splitting stages into substages and by reorganizing the TNM descriptors. However, this rearrangement seems to have failed in its goal of increasing the overall prognostic capability of the staging system, which ultimately depends on how accurately the TNM descriptors portray the disease. Because a derived variable cannot be more informative than the parental variables, it should be impossible to go beyond the TNM factors with any of their possible combinations. As acutely observed by Margolis,29 we do not need to group multiple and different TNM subsets into a unique stage. One might simply denote the TNM subsets that are being dealt with and calculate the stage at a later time, if necessary. This would be more responsive to the changes in clinical and research environments. It would avoid additional, nonessential classifications and would offer the greatest potential for a prognostic assessment and the best specificity for the individuation of groups at similar risk. In conclusion, there is a message from this study that we would like to emphasize. The message is that there is no need to place the various TNM subsets into stage groups. The next committee for the revision of the ISSLC might like to consider the pros and the cons of maintaining such a classification.
| Acknowledgements |
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| Footnotes |
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Received for publication July 1, 1999. Accepted for publication January 12, 2000.
| References |
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