MA25.09 M1b Disease in the 8th Edition of IASLC Staging of Lung Cancer: Pattern of Single Extrathoracic Metastasis and Clinical Outcom

Abstract

The 8th edition of IASLC staging of lung cancer has revised M classification and defined M1b disease for single extrathoracic metastasis, which is distinguished from M1c with multiple extrathoracic metastases. We investigated the prevalence of M1b disease in stage IV NSCLC patients (pts), and studied the pattern of single extrathoracic metastasis and its relationship with overall survival (OS). 567 pts with stage IV NSCLC (236 males, 331 females, median age: 63) diagnosed in 2008-2012 were reviewed to determine M stage according to the 8th edition of IASLC staging of lung cancer (M1a: separate tumor nodules in a contralateral lobe, pleural/pericardial nodule or effusion; M1b: single extrathoracic metastasis; M1c: multiple extrathoracic metastasis in one or more organs). Clinical characteristics and OS were compared according to M stage. Among 567 pts, 57 pts (10%; 95%CI: 7.6-13%) had M1b disease with single extrathoracic metastasis, while 119 pts (21%) had M1a and 391 pts (69%) had M1c disease. Squamous histology was more common in M1b (9/57; 16%) than in M1a (7/119; 6%) and M1c pts (22/391; 6%) (Fisher P=0.03). The median OS of M1b pts was 14.8 months (95%CI: 12.7-24.7 months), compared to 22.7 months (95%CI: 18.5-31.6 months) for M1a and 13.4 months (95%CI: 11.8-15.3 months) for M1c pts (log-rank P < 0.0001). Among 57 M1b pts, brain was the most common site of single metastasis (n=28; 49%), followed by bone (n=16; 28%), adrenal (n=7; 12%), liver (n=3; 5%), muscle (n=2; 4%), and distant node (n=1; 2%). M1b pts with liver metastasis had shorter OS than others (median OS: 8.1 vs. 16.1 months, log-rank P=0.046). Single metastasis in M1b pts were locally treated in 31 pts (54.5%). Brain metastasis was more frequently treated with local treatment than others (26/28, 92.9%vs. 5/29, 17%; p<0.0001). M1b disease was noted in 10% of stage IV NSCLC pts. Squamous histology was more common in M1b than in M1a and M1c groups. Brain was the most common site of single metastasis and was often treated locally. Single liver metastasis in M1b disease was associated with shorter OS. The study characterized the unique clinical features of the new category of M1b disease among stage IV NSCLC.