STK11 Mutated Lung Adenocarcinoma: A Molecular and Clinicopathologic Study

Targetable gene alterations have become increasingly important in the treatment of cancers. Thirty STK11-mutated lung cancers from 199 cases with molecular profiling performed during 2016–2024 were studied for clinical, morphologic, immunohistochemical (IHC) and molecular features. Of the 30 STK11-mutated lung cancers, 29 were lung adenocarcinomas (LADCs) and 1 was large cell neuroendocrine carcinoma (LCNEC). STK11 mutation was not found in other subtypes of lung cancers. Of the 29 STK11-mutated LADCs, 6 (21%) were mucinous and 23 (79%) were non-mucinous. Of the 19 non-mucinous LADCs with sufficient material for IHC, 9 (47%) displayed acinar/papillary/lepidic patterns, 8 (42%) were poorly differentiated (solid/trabecular/basaloid/complex glandular), and 2 (11%) had mixed solid and acinar patterns. The most common concurrent altered genes were KRAS (52%), followed by TP53 (38%), KEAP1 (34%), and DNA repair genes (BRCA2/ATM) (21%). A total of 6/15 (40%) LADCs with a KRAS mutation presented with mucinous morphology. Concurrent EGFR, ROS, or ALK alterations with STK11 mutation were rare or non-existent. Of the 3 LADCs with SMARCA4 deficiency, 2 were mucinous and 1 had basaloid/adenoid cystic-like features. All the cases were microsatellite stable (MSS). The majority (55%) had low TMB (<10). Most (86%) had PD-L1 TPS 0 or <5%. Among the 14 non-mucinous LADCs with IHC performed, 5 (36%) were TTF-1-negative and all displayed poorly differentiated morphology. Overall, 8/10 (80%) of poorly differentiated components in non-mucinous LADCs were negative for TTF-1. In contrast, all LADCs with better differentiated patterns (acini/papillary/lepidic) were positive for TTF-1. The majority (14/21, 67%) of patients with available follow-up presented with metastasis.