Role of Radiation Therapy in R1/R2 Resection and Prognostic Factors Associated With Survival in Thymoma

Abstract

To evaluate the role of radiation therapy (RT) in post-operative Thymoma with R1/R2 resections and to assess the prognostic factors associated with survival. All patients with thymoma subtype A, AB, B1, B2 and B3 diagnosed between 1996 and 2010 were identified using pathology database. Hospital medical records were retrospectively reviewed for patient characteristics and treatment details. Patients who underwent simple biopsy or those with histological type C or thymic carcinoma were excluded. For the purpose of this study any histological grades reported using the older classifications were reviewed by the pathologists and reclassified as per the WHO system. Patients were grouped according to treatment types; surgery alone versus surgery and adjuvant RT. Overall survival (OS), disease free survival (DFS), freedom from recurrence (FFR) for R0 resections and time to progression (TTP) for R1/ R2 resections were analyzed and compared using log-rank test. The Cox regression model was used to analyze the prognostic factors. A total of 210 patients were identified. The median follow up was 6.8 years. There were 60 stage I (28.6%), 108 stage II (51.4%), 35 stage III (16.7%) and 7 stage IV (3.3%). Histological subtypes were; 23 type A (11%), 48 type AB (22.9%), 34 type B1 (16.2%), 65 type B2 (31%) and 40 type B3 (19%). Ninety-nine patients underwent surgery alone (47.1%) and 111 underwent surgery and adjuvant RT (52.9%). The 10 year OS was 82.2% for surgery compared to 90.1% for surgery and RT (p=0.763). The 10 year DFS was 79.7% and 80.8% respectively (p=0.797). Subgroup analysis of patients with R1/R2 resections showed the 10 year OS of 53.6% with surgery and 91.8% with surgery and RT (p=0.005). The 10 year DFS was 57.1% and 78.1% (0.088) respectively. No differences were found in FFR or TTP between two treatment groups. Both univariate and multivariate analysis showed age, presence of Myasthenia Gravis (MG) and Masaoka stage (I/II versus III/IV) as significant factors associated with OS. Masaoka stage alone was significant for DFS. Histological subtypes (A/AB/B1 versus B2/B3) had no prognostic impact on survivals; OS p=0.730, DFS p=0.072. Adjuvant RT improved OS and DFS in R1/R2 resections. Age, presence of MG and Masaoka stage were found as significant factors associated with overall survival in thymoma.