[Leptomeningeal carcinomatosis as a rare metastatic spreading of BRAF-mutated microsatellite stable colon cancer].

Leptomeningeal carcinomatosis is a rare but serious complication of solid tumors such as melanoma, breast and lung cancer, as well as gastrointestinal carcinomas. Its clinical manifestation is highly variable, presenting as radicular pain with or without neurological deficits, as well as with headaches and hallucinatory irritation symptoms. Leptomeningeal carcinomatosis is often misdiagnosed, which delays treatment. Here we report a rare case of a patient with BRAF-mutated microsatellite stable colon carcinoma with lymphatic and skeletal metastases, who developed neurological symptoms one month after the initial diagnosis of malignancy. Based on the cytological detection of tumor cells in the cerebrospinal fluid, a leptomeningeal carcinomatosis was diagnosed, despite normal findings on MRI. Intrathecal chemotherapy with methotrexate, combined with intensive systemic immunochemotherapy, resulted in a good partial remission of the underlying malignant disease. However, approximately 8 months after the start of therapy, the patient developed progressive leptomeningeal carcinomatosis and died a few weeks later.