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.


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 < 0.01). Histopathologically, lymphocyte diminished markedly in type B1 thymoma, and both lymphocyte and epithelial cells diminished in type B2, whereas none of the B3 tumors showed any histologic change. The values of all the cases is 90.5% in complete resection, 19.0% in no combined resection of the adjacent organs, and 77.6% and 83.6% in overall and disease-free 10-year survival, respectively, and these value do not differ according to the WHO histologic criteria.


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.
Onuki
Takuya
T
Department of Chest Surgery and Radiation Oncology, Graduate School of Comprehensive Human Science, University of Tsukuba, Tsukuba, Ibaraki, Japan.
Ishikawa
Shigemi
S
Yamamoto
Tatsuo
T
Ito
Hiromichi
H
Sakai
Mitsuaki
M
Onizuka
Masataka
M
Sakakibara
Yuzuru
Y
Iijima
Tatsuo
T
Noguchi
Masayuki
M
Ohara
Kiyoshi
K
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001706:Biopsy; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005500:Follow-Up Studies; D006338:Heart Neoplasms / Q000473:pathology*; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology*; D008297:Male; D008479:Mediastinal Neoplasms / Q000473:pathology*; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D009367:Neoplasm Staging; D010496:Pericardium; D011300:Preoperative Care / Q000379:methods*; D012189:Retrospective Studies; D013934:Thymectomy / Q000379:methods*; D013945:Thymoma / Q000473:pathology* / Q000532:radiotherapy / Q000601:surgery; D013953:Thymus Neoplasms / Q000473:pathology* / Q000532:radiotherapy / Q000601:surgery; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome