Clinical course of stage IV invasive mucinous adenocarcinoma of the lung

An invasive mucinous adenocarcinoma (IMA) is a distinct lung adenocarcinoma variant. The characteristics of stage IV IMAs are relatively unclear since most previous studies described resected cases from stage I to III. The present study aimed to investigate the clinical course of stage IV IMAs and compare the findings to those of stage IV invasive non-mucinous adenocarcinomas (INMAs).The study included 36 IMA patients and 210 INMA patients. The clinicopathological parameters, treatment methods and responses, overall survival (OS), and progression-free survival (PFS) were evaluated.IMAs were predominantly located in the lower lobes and frequently presented with multifocal consolidation and lung-to-lung or pleural metastasis. KRAS mutations were noted in 60.0% of the examined IMAs. Non-TKI chemotherapy (CTx) was used in 72.2% of the IMA patients. OS was significantly better in untreated IMA patients than in untreated INMA patients. IMA patients treated with non-TKI CTx had no improvement of OS compared to the untreated IMA patients. However, among INMA patients, OS was best with TKIs in patients harbouring targetable mutations, followed by non-TKI CTx. IMA and INMA patients treated with non-TKI CTx had similar PFS.Stage IV IMAs have distinct clinicopathological characteristics, and they might be less aggressive than INMAs. Since non-TKI CTx might not be beneficial in IMA patients, new therapeutic approach is necessary.