10213- MET-17 A CASE OF METASTATIC BRAIN TUMOR FROM HER2-POSITIVE PAROTID CARCINOMA WITH LOCALIZED MENINGEAL DISSEMINATION

Abstract A 30s-year-old man was undergoing chemotherapy with intravenous trastuzumab for recurrent HER2-positive parotid carcinoma. Gamma knife therapy was given to a metastatic brain tumor of left frontal lobe in February X. The lesion was temporarily reduced in size, but in November X, local re-growth and a new lesion in the right frontal lobe were observed. He underwent ZAP-X fractionated stereotactic radiotherapy 24 Gray per 3 fractions for the left frontal lobe lesion and 20 Gray for the right temporal lobe lesion. In February X+1, he received ZAP-X stereotactic radiotherapy for a new lesion near the Sylvian fissure. He was admitted to the hospital with a diagnosis of meningeal carcinomatosis due to contrast findings in the cerebral gyrus from the left Sylvian fissure. Whole brain irradiation was avoided, and intrathecal methotrexate was administered. MRI scan in June X+1 showed multiple intraparenchymal brain metastases with surrounding brain edema and recurrent headaches, so steroids were prescribed and palliative care was continued. The number of cases of localized meningeal dissemination is expected to increase with advances in chemotherapy and the widespread use of stereotactic radiotherapy. The indication of Trastuzumab deruxtecan has been expanded to HER2-positive metastatic solid tumors abroad. It is expected to be available in Japan as soon as possible.