This phase III trial compares the effect of radiation therapy combined with hormonal therapy versus hormonal therapy alone in treating patients with low risk, early stage breast cancer with Oncotype Dx Recurrence =< 18. Oncotype DX is a laboratory test which results in a score that is used to help predict whether breast cancer will spread to other parts of the body or come back. Radiation therapy uses high doses of radiation to kill cancer cells and shrink tumors but may result in some side effects. Hormones called estrogen and progesterone may contribute to the growth of breast tumor cells. Hormone therapy, also called endocrine therapy, may stop the growth of tumor cells by blocking or removing these hormones. This clinical trial may help researchers understand if patients with low-risk, early stage breast cancer who have Oncotype recurrence score of =< 18 can safely omit radiation therapy and only be treated with hormonal therapy without losing any radiation treatment benefit.

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.