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.