Tucatinib Combined with Trastuzumab and TAS-102 for the Treatment of HER2 Positive Metastatic Colorectal Cancer in Molecularly Selected Patients, 3T Study

This phase II trial studies whether tucatinib combined with trastuzumab and TAS-102 works to shrink tumors in patients with HER2 positive colorectal cancer that has spread to other parts of the body (metastatic) and has one of the following gene mutations detected in blood: PIK3CA, KRAS, NRAS, or BRAF V600. Tucatinib is in a class of medications called kinase inhibitors. It works by blocking the action of the abnormal protein that signals tumor cells to multiply. This helps stop or slow the spread of tumor cells. Trastuzumab is a form of targeted therapy because it attaches itself to specific molecules (receptors) on the surface of tumor cells, known as HER2 receptors. When trastuzumab attaches to HER2 receptors, the signals that tell the cells to grow are blocked and the tumor cell may be marked for destruction by the body's immune system. TAS-102 is a combination of 2 drugs; trifluridine and tipiracil. Trifluridine is in a class of medications called thymidine-based nucleoside analogues. It works by stopping the growth of tumor cells. Tipiracil is in a class of medications called thymidine phosphorylase inhibitors. It works by slowing the breakdown of trifluridine by the body. Giving tucatinib, trastuzumab, and TAS-102 together may work better than usual treatment for metastatic colorectal cancer.