Biggs, Christopher

1517 Background: In a previous report, we showed in patients with newly diagnosed anaplastic oligodendrogliomas (AOs) and mixed anaplastic oligoastrocytomas (MAOs) that temozolomide (TMZ) can be given concurrently with radiation therapy (RT) with acceptable toxicity. We have now evaluated the efficacy of this regimen and correlated durability of response with tumor 1p/19q genotype. Methods: A phase II study was performed to evaluate the use of pre-RT TMZ followed by concurrent RT and TMZ in patients with newly diagnosed AO or MAO. The primary endpoint was to determine the pre-RT TMZ six-month progression rate, and secondary endpoints included progression-free survival and overall survival. Results: 40 eligible patients were entered into the trial. Thirty-two patients completed 6 months of pre-RT TMZ and concurrent RT and TMZ. Of the remaining eight patients, 4 withdrew due to toxicity and 4 other patients withdrew from study without evidence of toxicity or pre-RT progression. 1p/19q data are available in 37 cases; 23 tumors had loss of heterozygosity (LOH) of both 1p and 19q (double-deleted) while 14 tumors had LOH of either 1p or 19q (n = 3), or no LOH (n = 11). To date, 11 patients have experienced tumor progression; 1p/19q data are available for 10 of these cases (2 are double-deleted (2/23 = 9%), 8 have at least one intact chromosome (8/14 = 57%). Kaplan-Meier analysis demonstrates that progression free survival is significantly better for the double-deleted group (median time to progression not reached) than for the intact group (median time to progression = 15.2 months, p = 0.001). Overall survival is 98% (39/40) with a median follow-up of 17.5 months (2.8 - 31.1 months). Conclusions: LOH of both 1p and 19q is strongly correlated with a durable response of AO and MAO to a combined regimen of chemotherapy and radiation therapy. Tumors that are intact at 1p and/or 19q progress early despite an aggressive therapeutic regimen. These results suggest that future clinical trials should be prospectively stratified by tumor 1p/19q genotype. [Table: see text]