Skeletal Muscle Metastasis in Patients With SMARCA4-Deficient Thoracic Tumors: A Retrospective Cohort Study.

SMARCA4-deficient thoracic tumor (SDTT) is a malignant tumor with a poor prognosis that often presents with distant metastases at the time of clinical diagnosis. Skeletal muscle metastasis is a rare subtype of metastasis patterns, and there are limited studies about SDTT metastasis in skeletal muscle. Herein, we retrospectively analyzed the data of stage IV patients diagnosed with SDTT from May 2009 to June 2024. The clinical and genomic data, imaging features, and treatment information were collected. As a result, the study included 145 patients with metastatic SDTT, 17 with skeletal muscle metastases, and 128 without. The rate of skeletal muscle metastasis in SDTTs was 11.7%. Multivariate Cox regression analysis showed that skeletal muscle metastases (p = 0.014, hazard ratio 95% confidence interval [HR 95% CI] [2.90, 1.25-6.75]) and first-line chemoimmunotherapy (p < 0.001, HR 95% CI [0.31, 0.17-0.56]) were independent prognostic variables. Furthermore, patients with skeletal muscle metastases had a significantly shorter median overall survival (OS) than those without (13.20 vs. 18.6 months, p = 0.021) in metastatic SDTTs. The mutation rate of STK11 and KRAS was higher in the skeletal muscle metastasis group (62.50% vs. 15.52%, p = 0.008; 50.00% vs. 8.62%, p = 0.009). In conclusion, SDTTs exhibited a high rate of skeletal muscle metastases. Skeletal muscle metastases and first-line chemoimmunotherapy were independent prognostic factors for OS in SDTTs.