Postoperative irradiation in stage II thymomas: is it worth it?-shedding some light in the guidelines' gray zone

Thymomas are rare, indolent tumors. Early stages (I-II) benefit from surgical treatment, while locally advanced diseases (stages III-IV) usually require a multidisciplinary approach. The role of postoperative radiotherapy (PORT) on anterior mediastinum for radically resected Masaoka-Koga stage II thymomas remains controversial. This study aims to determine the impact of PORT on the disease-free survival (DFS) of stage II thymomas. We retrospectively collected the clinical and oncologic data [age, sex, myasthenia gravis (MG) prevalence, Masaoka-Koga stage, World Health Organization (WHO) histologic subtype] of those patients who underwent radical exeresis in our Unit between January 2000 and December 2020. Kaplan-Meier estimates of DFS were then performed. Our study included 195 patients (M/F = 98/97). Almost all patients were affected by MG (90.7%) and most of them were operated by median sternotomy (93.3%). Thymoma stage was IIa in 87 cases (44.6%) and IIb in 108 cases (55.4%). The most represented histologic subtype was AB (27.7%), followed by B2 (24.6%), A (19%), B1 (14.9%) and B3 (13.8%). PORT was performed in 113 patients (58%, 39 stage IIa and 74 stage IIb). During the surveillance, 8 patients (4.1%) presented pleural recurrences and no local relapses. DFS was comparable in stage IIa and IIb patients, independently from PORT administration (p = .395 and p = .858, respectively). Moreover, PORT did not affect DFS considering the histologic subtypes (p = .304 for A and AB thymomas, p = .608 for B1, B2 and B3 thymomas). In our wide series, PORT administration didn't show any additional benefit on DFS. Therefore, based on our experience, patients with stage II thymoma who underwent radical surgery should not undergo any local adjuvant treatment.