RET Fusion-Positive Lung Adenocarcinoma: Partner-Specific Clinicopathological Characteristics, Co-Mutation Profiles,...

RET fusions represent actionable oncogenic drivers in lung adenocarcinoma (LUAD). However, the clinicopathological features, co-mutation landscape, and therapeutic outcomes across different fusion partners remain incompletely characterized.

We retrospectively analyzed 268 patients with RET fusion-positive LUAD diagnosed between July 2017 and December 2024. Clinicopathological features, metastatic patterns, and concomitant genomic alterations were compared between KIF5B and non-KIF5B subgroups. Treatment outcomes of selective RET inhibitors, multikinase inhibitors (MKIs), and immunotherapy combined with chemotherapy were evaluated, with subgroup analyses according to fusion partners.

The median age at diagnosis was 58 years; most patients were female (57.0%) and never/light smokers (60.8%). Bone (12.3%), pleural (11.9%), and brain metastases (6.7%) were the most common metastatic sites. KIF5B-RET fusions were more frequently detected in earlier disease stages compared with non-KIF5B (p = 0.0531). Among 274 RET fusion events, KIF5B-RET was predominant (65%), followed by CCDC6-RET (16%) and NCOA4-RET (1%). Concomitant mutations were identified in 28.7% of patients, most commonly TP53 (39.0%) and CDKN2A (13.0%), with CDKN2A alterations predominantly consisting of functionally inactivating SNVs concurrent with shallow deletions more enriched in non-KIF5B (p = 0.0393). Nineteen patients received targeted therapy, including pralsetinib, selpercatinib, and cabozantinib, achieving an overall ORR of 57.9% and mPFS of 12.0 months. Notably, non-KIF5B patients demonstrated longer median PFS than KIF5B patients under pralsetinib (17.0 vs. 5.5 months, p = 0.0473). Fifteen patients received first-line immunochemotherapy, achieving a median PFS of 17.0 months, ORR of 40.0%, and DCR of 80.0%, comparable to targeted therapy (p = 0.3871).

RET fusion-positive LUAD comprises biologically heterogeneous subsets defined by fusion partners. KIF5B-RET tend to occur at earlier stages, whereas non-KIF5B are more frequently associated with CDKN2A co-mutations and may derive greater benefit from selective RET inhibition. Immunochemotherapy demonstrates comparable efficacy regardless of fusion partner, highlighting the need for partner-specific therapeutic strategies in RET fusion-positive LUAD.