Ctni-08. tucatinib, trastuzumab, and capecitabine with stereotactic radiosurgery in patients with brain metastases from her-2 positive breast cancer (tutor): a multicenter phase 1 clinical trial

Abstract BACKGROUND 20-40% of HER-2-positive breast cancer patients develop brain metastases (BMs), which are frequently tackled with stereotactic radiosurgery (SRS). Tucatinib, an oral HER-2 selective tyrosine kinase inhibitor (TKI), has demonstrated efficacy for HER-2-positive breast cancer in combination with capecitabine and trastuzumab. We hypothesize that a combinatorial approach for HER-2 positive breast cancer BMs (BCBM) will lead to better long-term control of BMs and systemic disease. METHODS This is an in-progress, prospective, single-arm, multicenter, phase 1 clinical trial that aims to determine the safety of combination of tucatinib, capecitabine, and trastuzumab with SRS in patients with HER-2 positive BCBM. Patients with age 18-80 years, ECOG 0-2, normal organ function, and up to 10 newly-diagnosed BMs are enrolled at six US centers. Any number of prior systemic therapies are allowed, except tucatinib and capecitabine. The primary endpoint of the study is the maximum tolerated dose (MTD) of tucatinib with SRS. This de-escalation study starts tucatinib at a dose level of 300 mg BID. Dose level -1 is 250 mg BID and level -2 is 200 mg BID. Upto 40 patients will be enrolled based on a 3 + 3 design. We plan to expand the cohort at MTD to 40 patients to assess the safety and efficacy of the combination. Secondary endpoints include efficacy as determined by response rate, intracranial PFS, extracranial PFS, and overall survival. Patients are administered oral tucatinib with SRS, followed by oral tucatinib for two weeks which is the dose-limiting toxicity (DLT) period. This is followed by tucatinib, trastuzumab, and capecitabine until progression or intolerable toxicity. DLTs are defined by Grade 3 or 4 thrombocytopenia, grade 4 anemia, grade 4 neutropenia lasting more than seven days, febrile neutropenia, and any non-hematologic toxicity of grade 3 or greater (excluding alopecia). The trial started enrollment in February 2023. Trial Information: NCT05553522.