Detection of Occult Micrometastases in Patients With Clinical Stage I Non-Small-Cell Lung Cancer: A Prospective Analysis of Mature Results of CALGB 9761 (Alliance)

Abstract

Purpose: Outcomes after resection of stage I non-small-cell lung cancer (NSCLC) are variable, potentially due to undetected occult micrometastases (OM). Cancer and Leukemia Group B 9761 was a prospectively designed study aimed at determining the prognostic significance of OM.

Materials and methods: Between 1997 and 2002, 502 patients with suspected clinical stage I (T1-2N0M0) NSCLC were prospectively enrolled at 11 institutions. Primary tumor and lymph nodes (LNs) were collected and sent to a central site for molecular analysis. Both were assayed for OM using immunohistochemistry (IHC) for cytokeratin (AE1/AE3) and real-time reverse transcriptase polymerase chain reaction (RT-PCR) for carcinoembryonic antigen.

Results: Four hundred eighty-nine of the 502 enrolled patients underwent complete surgical staging. Three hundred four patients (61%) had pathologic stage I NSCLC (T1, 58%; T2, 42%) and were included in the final analysis. Fifty-six percent had adenocarcinomas, 34% had squamous cell carcinomas, and 10% had another histology. LNs from 298 patients were analyzed by IHC; 41 (14%) were IHC-positive (42% in N1 position, 58% in N2 position). Neither overall survival (OS) nor disease-free survival was associated with IHC positivity; however, patients who had IHC-positive N2 LNs had statistically significantly worse survival rates (hazard ratio, 2.04, P = .017). LNs from 256 patients were analyzed by RT-PCR; 176 (69%) were PCR-positive (52% in N1 position, 48% in N2 position). Neither OS nor disease-free survival was associated with PCR positivity.

Conclusion: NSCLC tumor markers can be detected in histologically negative LNs by AE1/AE3 IHC and carcinoembryonic antigen RT-PCR. In this prospective, multi-institutional trial, the presence of OM by IHC staining in N2 LNs of patients with NSCLC correlated with decreased OS. The clinical significance of this warrants further investigation.

Fig 1.

Study schema for Cancer and Leukemia Group B (CALGB) 9761. Note requirement for sampling at least five nodal stations on the right side, six on the left side. CEA, carcinoembryonic antigen; IHC, immunohistochemistry; NSCLC, non–small-cell lung cancer; RT-PCR, reverse transcriptase polymerase chain reaction.

Fig 2.

CONSORT diagram: Patient enrollment and exclusion. NSCLC, non–small-cell lung cancer.

Fig 3.

(A) Hematoxylin and eosin stain of a lymph node found positive by immunohistochemistry (IHC) stain for cytokeratin. No tumor is apparent. Original magnification, ×100. (B) IHC stain for cytokeratin of the same node, different section. A small focus of tumor stained brown (arrow). Original magnification, ×100. (C) Higher magnification of tumor focus shown in Fig 3B. Original magnification, ×200. An IHC-positive focus of tumor in this node (arrow) had a maximum diameter of approximately 40 microns. Courtesy of Robin T. Vollmer, MD.

Fig 4.

(A) Overall survival by immunohistochemistry (IHC) status of lymph nodes in patients with stage I non–small-cell lung cancer. Log rank P = .19. (B) Disease-free survival by IHC status. Log rank P = .51.

Fig A1.

(A) Overall survival by polymerase chain reaction (PCR) status of lymph nodes in patients with stage I non–small-cell lung cancer. Log rank P = .15. (B) Disease-free survival by PCR status. Log rank P = .24.