Prevalence of autoimmune diseases in thymic epithelial tumors (TET) insights from RYTHMIC.

Abstract

9073 Background: TET are associated with autoimmune disorders (AID) in up to 30% of patients (pts). However, there have been wide variations in the reported prevalence of AID in TET pts in small single-center series. RYTHMIC (Réseau tumeurs THYMiques et Cancer) is a French network mandated to systematically discuss every case of TET. We aimed to describe the prevalence of AID in a large French population. Methods: RYTHMIC database, hosted by IFCT (Intergroupe Francophone de Cancérologie Thoracique), prospectively includes all consecutive pts with a diagnosis of TET discussed in French national or regional tumor boards. We analyzed epidemiologic, clinical and pathological characteristics of pts with TET’s related AID. Results: From January 2012 to December 2019, 2909 pts were included in the database. The mean age at diagnosis of TET was 54 and 52% were male. In the overall population, Masaoka Koga stages were well balanced with 12.6% (n = 187) stage I, 8.8% (n = 131) stage IIa, 8.4% (n = 124) stage IIb, 11.1% (n = 164) stage III and 8.5% (n = 125) stage IV. There were 364 (12.5%) events of AID in 302 pts. 62 pts (17%) had more than 1 AID. Among the events, 236 were myasthenia gravis (MG) (64.8%), 19 Hypo-gammaglobulinemia syndrome (5.2%), 15 pure red cell aplasia (4.1%), 18 thyroiditis (4.9%) and 16 systemic erythematous lupus (4.4%). Diagnosis of AID was mostly done at tumor diagnosis (n = 239, 65.7%) but some patient had AID diagnosed before diagnosis (n = 67, 18.4%) or during follow up (n = 32, 8.8%). Among pts presenting AID, B2 was the most common subtype (n = 133, 36.5%). The incidence of AID per subtype was as follow: A (n = 10/81, 12.3%), AB (n = 48/225, 21.3%), B1 (n = 35/130, 26.9%), B2 (n = 133/295, 45.0%), B3 (n = 46/113, 40.7%), thymic carcinoma (n = 16/275, 5.8%). Conclusions: The prevalence of AID in pts with TET was 12.5%, > 40% in B2 and B3 subtypes. Diagnosis of AID can be delayed compared to the diagnosis of TET. Immunotherapy indication should be carefully assessed in pts with TET other than thymic carcinoma.