This phase II trial compares the effect of capecitabine to endocrine therapy in patients with non-Luminal A hormone receptor-positive breast cancer that has spread from where it first started (primary site) to other places in the body (metastatic). In this study, patients submit a sample of tumor for testing to determine if their breast cancer is considered non-Luminal A. Only patients with non-Luminal A receive study treatment. In the future, doctors hope that this test can assist in picking the best treatment for patients with this type of cancer. Capecitabine is in a class of medications called antimetabolites. It is taken up by tumor cells and breaks down into fluorouracil, a substance that kills tumor cells. Endocrine therapy is treatment that adds, blocks, or removes hormones. To slow or stop the growth of certain cancers (such as prostate and breast cancer), synthetic hormones or other drugs may be given to block the body's natural hormones. Giving capecitabine as compared to endocrine therapy may kill more tumor cells in patients with metastatic breast cancer.

This phase II/III trial aims to determine the type of chemotherapy that will benefit patients who have had surgery for their stage II or III colon cancer based on presence or absence of circulating tumor deoxyribonucleic acid (ctDNA). In ctDNA positive patients, this trial compares the effect of usual chemotherapy versus mFOLFIRINOX. In ctDNA negative patients, this trial compares the effect of usual chemotherapy versus ctDNA testing every 3 months to determine which approach might be better to prevent colon cancer from returning. Oxaliplatin is in a class of medications called platinum-containing antineoplastic agents. It works by damaging cells DNA and may kill cancer cells. Leucovorin is in a class of medications called folic acid analogs. It works by protecting healthy cells from the effects of chemotherapy medications while allowing chemotherapy agent to enter and kill cancer cells. Fluorouracil is in a class of medications called antimetabolites. It stops cells from making DNA and may slow or stop the growth of cancer cells. Capecitabine is in a class of medications called antimetabolites. It Is taken up by cancer cells and breaks down to a substance that kills cancer cells. Irinotecan is in a class of antineoplastic medications called topoisomerase I inhibitors. It works by stopping the growth of cancer cells. This trial may help doctors determine what kind of chemotherapy to recommend to colon cancer patients based on the presence or absence of ctDNA after surgery for colon cancer.