A Study of Tucatinib Given Before Surgery to People With HER2+ Cancers That Have Spread to the Brain

The purpose of this study to see how the brain absorbs, distributes, and gets rid of tucatinib in people who have HER2+ cancers (breast cancer, NSCLC, CRC, or GEC) that have spread to the brain, and to learn more about how cancer cells develop resistance to treatment. The researchers will do research tests to look for genetic differences between HER2+ breast cancer that has spread to the brain and progressed during treatment with tucatinib and cancers that are being treated with tucatinib for the first time.

All patients will receive tucatinib per-protocol at standard dose of 300 mg orally twice daily on days - 4, -3, -2, -1 and day 0 (in AM). The post-surgery treatment (systemic and/or local) will be decided according to treating physician discretion and is not a study intervention. Tissue samples of brain metastases along with blood/plasma and CSF samples will be analyzed to evaluate brain tumor penetration of tucatinib as well as biologic response to tucatinib in patients with brain metastases from HER2+/mutant breast cancer who are undergoing clinically indicated brain surgery. Patients may continue tucatinib post-operatively at the discretion of the treating oncologist with monitoring as per clinical routine; this is not a study intervention for Cohort A and Cohort B. Patients on Cohort C may receive tucatinib post-operatively through the study according to physician descretion.