Pathologic Radioresponse of Preoperatively Irradiated Invasive Thymomas

Background We have been applying preoperative radiotherapy (RT) to Masaoka stage III thymomas intending to make surgical resection more complete by reducing mass volume, to prevent possible dissemination caused by surgical manipulation and to get better survival as a result. However, the radioresponses vary from tumor to tumor. We hypothesized that thymoma is a variable radioresponsive tumor depending on pretreatment histology. Materials and Methods Twenty-one of stage III thymomas underwent preoperative RT plus surgery followed by postoperative RT between 1982 and 2004. Reduction ratios, histopathologic changes according to WHO histologic criteria, resectability, long-term survival, and disease control, by preoperative RT were analyzed. Results Pretreatment WHO subtypes were type AB ( n = 1), B1 (5), B2 (6), B3 (4), and unclassified (5). Sixteen tumors (76.2%) decreased in size after preoperative RT with a mean (median) reduction ratio of 30.8% (27.0%). Type B1or B2 group had higher reduction ratio than type B3 group (mean value of 39.7%, 31.8%, and 21.0%, respectively, p Conclusions This modality at modest doses was macroscopically and histopathologically effective on tumors particularly in WHO B1 and B2 thymomas than WHO B3 thymoma. The therapeutic benefit of preoperative RT followed by surgery and postoperative RT for stage III thymomas should be defined thoroughly.