IS POSTOPERATIVE RADIOTHERAPY FOR THYMOMA EFFECTIVE

Objective The authors determined the effect of postoperative mediastin al irradiation in preventing local and pleural recurrences of thymoma. Summary Background Data The role of mediastinal irradiation after inc omplete resection or biopsy of an invasive thymoma is well established . However, routine use of adjuvant mediastinal irradiation for patient s with thymoma after complete resection remains controversial. Methods During the 19-year period from 1973 to 1992, operations were performe d on 89 patients with thymoma. Of these 89 patients, 80 patients who u nderwent gross complete tumor resection including adjacent tissues tha t appeared to be invaded by tumor were selected for this study. The ef fects of postoperative mediastinal irradiation on the recurrence rate of thymoma were analyzed according to histologic type, clinical stage, and whether adhesions to or invasion of the pleura or pericardium wer e present. Results Recurrence of thymoma was observed in 13 of 80 (16. 3%) patients. No recurrence was observed in 23 patients with noninvasi ve thymoma. In patients with invasive thymoma whose tumor was macrosco pically adherent to the pleura but not microscopically invasive (p1), recurrence was observed in 4 of 11 patients (36.4%) when mediastinal i rradiation was not performed, but in none of 10 patients who received mediastinal irradiation. However, in patients with microscopic pleural invasion (p2), a high recurrence rate was observed with mediastinal i rradiation (40%, 6/15 patients) or without mediastinal irradiation (30 %, 3/10 patients). Postoperative mediastinal irradiation for patients with microscopical invasion to pericardium (c2) did not decrease the r ecurrence rate. Analysis of the mode of recurrence showed that mediast inal irradiation may have been effective in preventing local recurrenc e, but it did not control the pleural dissemination that was observed in 12 of 13 recurrent cases. Conclusions Mediastinal irradiation is no t necessary for patients with noninvasive thymoma. In patients with in vasive thymoma, postoperative mediastinal irradiation is effective in preventing recurrence in patients with p1 thymoma, but not in patients with p2 or c2 tumors. Further adjuvant therapy should be performed to supplement mediastinal irradiation in patients with p2 or c2 thymoma, even after complete resection.