Pathological and Clinical Features of Enteric Adenocarcinoma of the Thymus. A Pooled Analysis of Cases from a Reference Center and Systematic Review of the Literature

Background: Primary enteric adenocarcinoma of the thymus (EAT) is a recently proposed rare subtype of thymic carcinoma. Unlike thymic carcinomas with squamous histology, for which clinical guidelines are available, little knowledge is available regarding the clinical and pathological features of EAT, and there is no consensus on the best treatment algorithm for such tumors.

Methods: We performed a systematic review of the literature, searching for all cases of EAT reported. We also retrospectively reviewed all cases of EAT treated at the European Institute of Oncology (IEO) between January 2000 and January 2020. Individual patient data were extracted and analyzed in order to delineate clinical and pathological features, as well as patients' prognosis and treatments outcome, evaluated in terms of Disease free Survival (DFS), Progression free survival (PFS) and overall survival (OS).

Results: Thirty-three cases (29 reported in literature and 4 new cases treated at IEO) of thymic adenocarcinoma deploying enteric differentiation as defined by WHO-criteria were analyzed. All tumors showed positive immunoreactivity for cytokeratin (CK) 20 and/or caudal type homeobox 2 (CDX2). Data on molecular profiling by next-generation sequencing were available in only 3 cases, and did not show actionable findings. At diagnosis, 11 pts had an early-stage (Masaoka I-II) and 22 a locally advanced (10 pts) or metastatic (12 pts) disease. Median-DFS of patients with localized disease was 12 months (95% CI, 7-19). Patients who received systemic chemotherapy were mostly treated with regimens commonly used for thymic epithelial tumors, with a discouraging PFS of 3-5 months for patients with stage IV disease. Median OS of the whole population was 34 months (95% CI, 24-NA:. mOS was not reached for patients with stage I-II disease versus 34 months in stage III-IV (p < 0.05).

Conclusion: Available evidence suggests that EAT represents a distinct entity in the context of thymic epithelial tumors, characterized by aggressive clinical behavior, poor responsiveness to chemotherapy and dismal patients prognosis. More research is needed to better define optimal management strategies for patients with such rare disease.