And those patients whose tumors would not respond to chemotherapy can avoid the side effects of those powerful drugs. The collaborative study results from the combined expertise of the two research teams. Oligodendrogliomas make up at least 10 percent of malignant gliomas, representing several thousand patients diagnosed in North America each year. For the one-third that do not respond to chemotherapy, the outlook is poor, with survival rates of one to two years after treatment with radiation therapy, the treatment for most malignant brain tumors. Microscopic examination of oligodendrogliomas shows no difference between the tumors that do and do not respond to chemotherapy.
Some tumors show only one change while others show combinations of two or three.
To test the hypothesis that genetic patterns might correspond with a tumor's chemosensitivity, the MGH team examined DNA samples from 39 oligodendroglioma patients treated by Cairncross and his colleagues and compared the specific genetic changes with each patient's outcome. They found that tumors with the chromosome 1 loss all responded to chemotherapy, while those without chromosome 1 loss responded far less frequently. Patients whose tumors had chromosome 1 loss also had markedly better survival. The chromosome 19 loss also was associated with longer survival, and the chromosome 9 deletion was associated with a worse prognosis. But overall, the chromosome 1 abnormality was the most powerful and significant factor associated with response to chemotherapy.