The Rare Entity of Basaloid Thymic Carcinoma: A Multicentric Retrospective Analysis from the Italian Collaborative Group for ThYmic MalignanciEs (TYME).

Background: thymic basaloid carcinoma (BTC) is an extremely rare tumor, and very little data are available on BTC's biology, clinical behavior, drug sensitivity, and patient outcomes.

Methods: We performed a retrospective observational study on patients diagnosed with BTC in 11 referral centers of TYME. All BTC diagnoses were reviewed by the referring pathologist.

Results: Twenty-eight patients were identified. A total of 22/28 patients were included. Eighteen patients had TNM stage I-III disease, and all underwent surgery; three patients received preoperative chemotherapy, and 10 patients received adjuvant radiotherapy. With a median follow-up of 46 (1-133) months, median overall survival (mOS) and median relapse-free survival were not reached. At 48 months, OS was 77% (95%CI 43-92), and DFS was 63% (95%CI 30-83). The median OS of the 4 patients diagnosed with metastatic disease was 7 months. Six patients received first-line systemic treatment for metastatic disease, and all showed tumor responses. Anti-tumor activity was also observed with an anti-VEGFR TKI and a multi-TKI inhibitor combined with an anti-PD1 antibody. Next-generation sequencing performed in three tumor samples did not identify actionable alterations or microsatellite instability.

Conclusions: BTC is an extremely rare tumor that usually presents as a localized disease. Patients diagnosed with stage I-III disease can achieve long-term DFS, and efforts should be made to perform radical surgical resection combined with perioperative treatment whenever appropriate. Patients with advanced disease progression have a poor prognosis despite a high response rate to systemic treatments.