BIOM-58. RE-INDUCTION OF INTRATHECAL CHEMOTHERAPY IN PRIOR RESPONDERS AND CORRELATION WITH CEREBROSPINAL FLUID CIRCULATING TUMOR CELLS

Abstract INTRODUCTION Leptomeningeal carcinomatosis (LMC) is an aggressive form of metastasis, with a historically poor median overall survival. Newer therapies and treatment strategies are improving outcomes, and more long-term responders exist. However, there are limited options for intrathecal (IT) chemotherapy, and re-induction in prior responders may be a reasonable treatment strategy. In addition, quantitative cerebrospinal fluid circulating tumor cells (CSF CTCs) are a valuable tool in LMC, for both surveillance of recurrence and evaluation of response. METHODS We retrospectively identified 10 patients with LMC who showed a response to IT chemotherapy and were followed with quantitative CSF CTCs on a commercially available platform. At progression, patients underwent re-induction of IT chemotherapy, on a twice a week schedule, and were evaluated for response. RESULTS All 10 patients were treated with re-induction IT chemotherapy. Six patients were re-challenged with topotecan, 3 with topotecan + trastuzumab, and 1 with pemetrexed + trastuzumab. Six patients had a primary diagnosis of breast cancer, three with lung cancer and one with ovarian cancer. The median KPS was 70. Eight were female. Prior to re-induction, all 10 had an increase in quantitative CSF CTCs. Only 1/10 had new symptoms, and 5/10 showed imaging changes on MRI. At the time of re-induction, 3/10 also received stereotactic radiosurgery to brain metastases and 2/10 had a change in systemic chemotherapy. 9/10 had improved CSF CTC counts on the next restaging, typically at 8 weeks. The median overall survival from re-challenge was 12.7 months. CONCLUSION Quantitative CSF CTCs were a more sensitive predictor of recurrence than symptoms or imaging, and were a marker of response to re-induction IT chemotherapy. Re-induction showed a durable survival benefit, and is a reasonable treatment strategy in patients who were prior responders