There remains a controversial issue of prophylactic radiation of the entire cranium in the case of certain tumors, particularly small cell lung cancer. Information from a trial by Slotman and colleagues and an older one by Aupérin and coworkers in patients with chemotherapy-responsive small cell lung cancer suggests that prophylactic radiation prolonged survival by 1.5 months and markedly reduced the later emergence of metastasis to the brain. Critics have noted that, with recently improving survival rates, the later cognitive effects of brain radiation may become evident.
In patients with a single parenchymatous metastasis (shown to be solitary by gadolinium-enhanced MRI), surgical extirpation may be undertaken provided that growth of the primary tumor and its systemic metastases is under good control and the metastasis is accessible to the surgeon and not located in a strategic motor or language area of the brain. Usually, excision is followed by radiation therapy to the entire brain. Patchell and coworkers have shown that survival and the interval between treatment and recurrence are longer and that the quality of life is better in patients treated in this way than in comparable patients treated with whole-brain radiation alone. Single or dual metastases from renal cell cancer, melanoma, and adenocarcinoma of the gastrointestinal tract lend themselves best to surgical removal, as implemented in the matched cohort study by Bindal and colleagues.
There is increasing evidence that some metastatic brain tumors are sensitive to chemotherapeutic agents, especially if the primary tumor is similarly responsive. Intrathecal and intraventricular chemotherapy are not thought to be of value in the treatment of parenchymal metastases. Immunotherapy has not yet been widely employed for brain metastases but this is rapidly changing, for example with melanoma and lung cancer.
Prophylactic antiepileptic drugs are generally not employed as they do not appear to prevent a first seizure, as mentioned earlier. Several studies, some well controlled, corroborate this as discussed in Chap. 15.
Despite all of these measures, survival is only slightly prolonged by treatment. The average period of survival in cases of brain metastases, even with therapy, is about 6 months, but it varies widely and is dominated by the extent of other systemic metastases. Between 15 and 30 percent of patients live for a year and 5 to 10 percent for 2 years; with certain radiosensitive tumors (lymphoma, testicular carcinoma, choriocarcinoma, some breast cancers), however, survival can be much longer. It has been stated, without strong corroboration, that patients with bone metastases tend to live longer than those with brain and meningeal metastases.
Widespread dissemination of tumor cells throughout the meninges and ventricles, a special form of metastatic cancer, is the pattern in approximately 5 percent of cases of adenocarcinoma of breast, lung, and gastrointestinal tract, melanoma, childhood leukemia, and systemic lymphoma. This is among the most deceptive of neurologic diagnoses. With certain carcinomas, notably gastric, it may be the first manifestation of a neoplastic illness, although more often the primary tumor has been present and is under treatment.