Central Nervous System Metastases in Thymic Epithelial Tumors: A Brief Report of Real-World Insight From RYTHMIC.

Thymic epithelial tumors (TETs) are rare malignancies ranging from indolent thymoma A to aggressive thymic carcinomas (TCs). Brain metastases are extremely infrequent for TETs and have only been described in case reports or small single-center series. RYTHMIC (Réseau tumeurs THYMiques et Cancer) is a French nationwide network mandated to systematically review every TET case and prospectively includes all consecutive patients discussed by national or regional tumor boards. We analyzed patients with TETs and central nervous system (CNS) metastasis during their cancer history from this large French registry. In an 8-year period, 2909 patients were included in the database, including 248 TCs (8.5%). A total of 14 patients had CNS metastases, five (36%) at diagnosis and nine (64%) at relapse. Among them, 12 patients (86%) had a diagnosis of TC and two (14%) had thymoma A and B3. Surgical biopsies were performed, and the histologic subtype for non-TC tumors was centrally confirmed. Median overall survival was 22 months (95% confidence interval [CI]: 9.8-34.2), with longer, albeit not significant, overall survival when CNS metastases were present at diagnosis versus relapse (not reached versus 17 mo; p = 0.29); median progression-free survival was 13 versus 8 months (p = 0.06), respectively. A higher risk of death (hazard ratio = 5.34, 95% CI: 1.3-21.9, p = 0.02) and relapse (hazard ratio = 1.89, 95% CI: 0.9-3.7, p = 0.06) was observed for patients suffering from TC with brain metastases compared with those without CNS extension. CNS disease was extremely rare in our TET cohort (0.48%), reported at both diagnosis and progression, present primarily in TC, with prevalence rising to 4.9%.