Detection of Occult Micrometastases in Non-Small Cell Lung Carcinoma by Reverse Transcriptase-Polymerase Chain Reaction

¹ From the Department of Surgery, University of Minnesota, and the Departments of Medical Oncology, Pulmonology, Gastroenterology, and Pathology, Minneapolis V.A. Medical Center, Minneapolis

Background: The 5-year survival rate following surgical resection of Stage I or Stage II non-small cell lung carcinoma (NSCLC) is 30% to 50%, probably because of undetected occult micrometastases (OMs) at the time of surgery. Other investigators have detected OMs in bone marrow and histologically negative lymph nodes from patients with NSCLC using immunohistochemical staining to cytokeratins and cell surface glycoproteins.

Study objective: To develop and evaluate an assay based on the reverse transcriptase-polymerase chain reaction (RT-PCR) for the detection of OMs in NSCLC.

Patients: Twenty-eight patients with benign or malignant thoracic pathology. Samples of primary tumors and lymph nodes were collected at the time of surgical resection or mediastinoscopic lymph-node biopsy.

Results: Using RT-PCR to detect messenger RNA (mRNA) transcripts for MUC1 (a cell surface glycoprotein present in lung tissue but absent from normal lymph nodes), OMs were identified in 33 of 88 lymph nodes determined to be free of tumor by hematoxylin and eosin staining. Eleven of 11 control mediastinal lymph nodes from patients without malignancy failed to express detectable MUC1 transcripts. Dilutional experiments demonstrate that the assay can detect one MUC1-positive NSCLC cell in 1x10⁷ MUC1-negative cells. A comparison of our RT-PCR assay to immunohistochemistry specific for the MUC1 glycoprotein suggests that RT-PCR may be more sensitive than immunohistochemistry for the detection of NSCLC OMs.

Conclusions: This study demonstrates that RT-PCR for MUC1 mRNA can detect the presence of MUC1 mRNA in histologically negative lymph nodes from patients with NSCLC. The prognostic significance of these findings is currently unknown.

Key Words: micrometastases • MUC1 • NSCLC • restaging • reverse transcriptase-polymerase chain reaction

Submitted on July 8, 1997
Accepted on October 31, 1997

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