Tumor, node and metastasis classification of lung cancer--M1a versus M1b--analysis of M descriptors and other prognostic factors.

Introduction: The current edition of the tumor, node and metastasis (TNM) classification of lung cancer (LC) divides the presence of metastasis (M1) into two categories: M1a and M1b, depending on its anatomical location. To assess this new classification, the survival and the M descriptors of LC patients with metastatic disease registered by the Bronchogenic Carcinoma Cooperative Group of the Spanish Society of Pneumology and Thoracic Surgery II (GCCB-S-II), were analyzed.
Methods: Non-small cell lung cancer (NSCLC) patients, with M1a or M1b disease, included in the GCCB-S-II, from April 2009 to December 2010, staged in accordance with the prospective staging project protocol of the International Association for the Study of Lung Cancer (IASLC), and with complete TNM staging and follow-up data, were studied. The overall survival associated with each M1 category and each M descriptor, besides other prognostic factors (sex, age, performance status [PS] and others) were analyzed by univariate and multivariate models.
Results: 640 NSCLC patients (195 M1a and 445 M1b) were included. M1b tumors had significantly worse survival than M1a tumors (p < 0.001). The prognostic value of M1 category was independent from other prognostic variables such as PS, weight loss, and others. The number of metastatic sites (isolated versus multiple) and the number of lesions (single versus multiple) in patients with isolated metastasis showed prognostic value, especially in those with brain metastasis.
Conclusion: The current division of the M1 category into two subsets (M1a and M1b) is warranted by their prognostic significance. The number of metastatic sites and the number of lesions in patients with isolated metastasis should be taken into account, because they also have prognostic relevance.
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