The International Association for the Study of Lung Cancer Staging Project: The Database and Proposal for the Revision of the Staging of Pulmonary Neuroendocrine Carcinoma in the Forthcoming Ninth Edition of the TNM Classification for Lung Cancer.

Summary

Using a large international database, the IASLC validated proposed TNM9 refinements for pulmonary NEC: N2a/N2b for single versus multiple ipsilateral mediastinal/subcarinal stations and M1c sub-stratification (M1c1 vs M1c2). These changes held robustly for SCLC; LCNEC showed consistent stage–survival gradients despite smaller numbers.

Key Findings

• Validated N2 subcategories: N2a (single ipsilateral mediastinal/subcarinal station) vs N2b (multiple stations) in SCLC.
• Validated M1c sub-stratification: M1c1 (multiple lesions in one extrathoracic organ system) vs M1c2 (multiple organ systems).
• LCNEC data showed decreasing survival with increasing clinical/pathologic stages despite smaller sample sizes.

Clinical Implications

Adopt TNM9 for SCLC/LCNEC, using N2a/N2b to distinguish single vs multiple ipsilateral mediastinal stations and M1c1/M1c2 to stratify extrathoracic metastatic burden; this should inform prognosis, surgical/RT decisions, and trial stratification.

Limitations

• LCNEC analyses were limited by smaller numbers, restricting full validation across all subgroups.
• Retrospective registry design may harbor residual staging or treatment heterogeneity.

Future Directions

Prospective validation of TNM9 in LCNEC, integration with molecular subtyping, and alignment with treatment algorithms and trial eligibility criteria.