Objective: The TNM 8 lung cancer staging system reclassifies patients with a solitary extrathoracic metastasis as M1b and two or more extrathoracic metastases as M1c. This study investigates the clinical relevance of this change.
Methods: Advanced lung cancer patients were retrospectively restaged according to the TNM8 M1b and M1c classifiers. Overall survival was compared in M1b and M1c patients staged with and without PET-CT. We then summarized the TNM 8 staging classification and the relevant literature on the treatment of oligometastatic lung cancer.
Results: In all, 82 patients with metastatic lung cancer were reclassified according to the TNM 8: 14 had M1b and 58 had M1c disease. Those with M1b disease lived significantly longer than those with M1c disease (15.2 vs. 7.3 months, p = 0.0029). Among those with M1b disease, survival was the highest when M1b status was confirmed by PET-CT (21.4 vs. 7 months). M1c patients with 4 or less distant metastases had a trend to longer survival vs. M1c patients with 5 or more metastases (9.4 vs. 7.3 months), especially when PET-CT staging was used (13.9 months).
Conclusions: We confirmed the prognostic value of the M1b and M1c descriptors in a Western European tertiary care population. The use of PET-CT seems to increase the prognostic value of the M descriptor and may define an additional oligometastatic subgroup of M1c patients. Clinical trials investigating the treatment of patients with varying degrees of metastatic disease are needed and should be based on PET-CT staging.
Keywords: Lung cancer; Metastasis; Oligometastatic; Stage IV; Staging.