Let’s go on and talk about another tumor type, that being oligodendroglioma. Although this is a very uncommon tumor, I think medial oncologists will increasing see a number of these patients for reasons you’ll see in a second.
Oligodendrogliomas are only about one-tenth as common as astrocytic tumors with peak incidence of this tumor occurs in young to middle-age adults, accounting for approximately 6% of all intracranial neoplasms in this age group. They are particular rare in the young or the elderly.
Standard treatment for this disease is complete surgical resection, if they are standard low grade oligodendrogliomas.
If you can remove them, patients are often tumor free for years, sometimes for decades. Radiation therapy appears to be of more questionable benefit in these patients than for astrocytic tumors. They appear to be more radio-resistant. There is a sub-group of oligodendrogliomas however that are known as anaplastic or malignant oligodendrogliomas. These are tumors that can infiltrate widely and also spread throughout the craniospinal axis via the CSF. Even rarely spread systemically. Again, these are relatively radio-resistant tumors however recently it has been demonstrated that these tumors can be exquisitely chemotherapy sensitive. And in fact can be some of the most chemotherapy sensitive of all solid tumors anywhere.
A number of different agents have been shown to be potentially effective in the treatment of this disease, mostly alkylating agents have been shown to be most effective. The first and probably the most complete demonstration of the potential chemotherapy sensitivity of these tumors was a study published by Conquest Group out of the National Cancer Institute of Canada where 24 eligible patients with anaplastic oligodendrogliomas were treated. Of those 24 patients there were 17 objective responses, including 7 complete remissions, some of which were maintained for several or a number of years without further therapy. These can be extremely chemotherapy sensitive tumors. These are rare tumors but a potentially even more significant finding was the realization that a more common tumor, known as a mixed glioma – which are tumors composed of both astrocytic components as well as oligodendroglioma components – may in fact also be similarly chemotherapy sensitive as shown by this rather complicated slide here. Mixed gliomas actually can account for almost one-third of all gliomas. So what’s beginning to be seen is the possibility that oligodendroglioma features within a tumor may in fact predict for chemotherapy sensitivity.