THE ROLE OF POSTOPERATIVE IRRADIATION IN THE TREATMENT OF OLIGODENDROGLIOMA

Purpose: Controversy regarding the role of adjuvant radiation therapy for the treatment of oligodendroglioma continues to exist. To better d efine the utility of postoperative irradiation for this tumor, the exp erience at the University of Washington was retrospectively examined. Methods and Materials: The histologic samples of 63 patients given the diagnosis of oligodendroglioma were reviewed by a panel of neuropatho logists and 41 were classified as pure oligodendroglioma. The two trea tment groups included 14 patients treated with surgery only and 27 who received surgery and postoperative radiation and were analyzed using univariate and multivariate analysis with respect to prognostic factor s, freedom from relapse, and survival. Results: Univariate statistical analysis of 14 clinical variables showed that a poorer prognosis was associated in patients with high cell density (p = .008), necrosis (p = .017), hemiparesis (p = .026), and papilledema (p =.091), while pati ents presenting with seizures had a better prognosis (p = .0096). Mult ivariate analysis showed necrosis (p = .001) and hemiparesis (p = .02) to be associated with decreased survival. Multivariate and univariate analysis of the treatment groups found them to be homogenous with res pect to prognostic factors. Survival times were significantly longer i n the group treated with postoperative irradiation (median survival ti me 84 vs. 47 months, p = .032). The 5 and 10 year survival rates were 83% and 46%, respectively, for the irradiated patients compared with 5 1% and 36% for those treated with surgery alone. Freedom from tumor re currence times were also longer in irradiated patients (median relapse free time 79 vs. 42 months, p = .01). Conclusion: Based on the result s of this study, we recommend continuing the practice of treating olig odendroglioma with postresection irradiation until a prospective multi center clinical trial is conducted to thoroughly evaluate the role of postoperative irradiation in the treatment of this tumor.