Invasive thymoma – Which patients benefit from post-operative radiotherapy?

Background The aim of this study is to identify patients with thymoma who should receive post-operative radiotherapy. Methods The Surveillance, Epidemiology, and End Results database was queried for stage IIB–IV thymoma patients diagnosed during 1988–2015. We analyzed the prognostic implications of various clinical–pathological factors by comparing the outcomes of those who received surgery with and without post-operative radiotherapy. Results A total of 1120 patients were identified; 62% received post-operative radiotherapy and 38% underwent surgery alone. In a propensity-matched cohort of 812 patients, no survival difference was seen in World Health Organization A, AB, B1, B2, or B3 tumors with the addition of post-operative radiotherapy to surgery (p>0.05). Post-operative radiotherapy also did not improve survival over surgery alone for tumors ≥ or < less than the 4 cm, 7 cm, 10 cm, and 13 cm cutoffs, all p>0.05. Post-operative radiotherapy was an independent, positive prognostic indicator only in the subgroup with stage III disease and in those receiving chemotherapy in addition to post-operative radiotherapy, both p<0.05. Conclusions Patients with stage III thymoma are most likely to benefit from the addition of post-operative radiotherapy to surgical treatments. Tumor size or World Health Organization histology alone should not be criteria for determining the need for post-operative radiotherapy in locally advanced thymoma. Masaoka–Koga stage, which has traditionally been used to help make such decisions, appears to be the most reliable determinant of the use of post-operative radiotherapy.