Meningeal carcinomatosis in breast cancer. Prognostic factors and influence of treatment. In 58 breast cancer patients with meningeal carcinomatosis (MC) pretreatment characteristics, clinical course, and response to treatment were evaluated. Forty-four patients were uniformly treated with intraventricular chemotherapy. Fourteen patients did not receive intraventricular treatment. In the intraventricularly treated group the median survival was 12 weeks. Multivariate analysis of the pretreatment characteristics of the intraventricularly treated patients demonstrated a prognostic significance with respect to survival for age older than 55 years, lung metastases, cranial nerve involvement, cerebrospinal fluid (CSF) glucose less than 2.5 mmol/l, and CSF protein 0.51 to 1.0 g/l. Based on the significance of these predicting factors a prognostic index (PI) identified four groups of patients with a median survival of 43 weeks, 22 weeks, 11 weeks, and 3 weeks, respectively. After 6 weeks of intraventricular treatment 22 patients showed a neurologic improvement or stabilization, and nine patients showed a worsening of the neurologic signs, whereas 13 patients (30%) had already died. The responders had a median additional survival of 5 months versus 1 month for nonresponders. No relation was found between survival and intensity of the intraventricular treatment after the first 6 weeks of treatment. Almost all long survivors had also received systemic treatment for systemic disease, whereas most patients who died within 6 months did not receive systemic therapy. Radiation therapy had no influence on the survival time. Early death due to the intensive treatment occurred in three patients. In 11 of the 17 patients who survived more than 4 months an often seriously debilitating late neurotoxicity developed. The survival curve of the nonintraventricularly treated patients appeared to be essentially the same as the curve of the intraventricularly treated patients. Using the same PI the predicted survival time was also the same as in the intraventricularly treated group. It is concluded that survival in MC from breast carcinoma may be more dependent on some pretreatment characteristics than on treatment intensity. On the basis of these pretreatment characteristics the survival time seems to be predictable. Finally, late neurotoxicity due to aggressive treatment leads to impairment of the quality of life in more than 50% of the long survivors. The exact value of intraventricular and systemic therapy in patients with MC still has to be determined. 