Investigators from the UCLA Jonsson Comprehensive Cancer Center, the Broad Institute, the Parker Institute for Cancer Immunotherapy and the Fred Hutchinson Cancer Institute used the genetic analyses of more than 1,200 colon cancers from the Cancer Genome Atlas, the Nurses' Health Study and the Health Professionals Follow-up Study.
Researchers studied their outcomes, including whether or not cancer recurred, and their overall survival.
Dr Harold Burnstein, from the American Society of Clinical Oncology, said: "This study will transform care immediately, and for the better".
'I'm delighted. I've been anxious for a long time about unnecessary treatment for cancer, and unnecessary side effects from chemotherapy, ' Dr. Otis Brawley, the chief medical and scientific officer for the American Cancer Society who was not part of the study, said.
Commenting on the findings, Dr Simon Vincent, director of research at Breast Cancer Now, said the research was "world class". A 2017 study showed that for breast cancer that hasn't spread to the lymph nodes, the rate of chemotherapy has dropped from around 27 percent in 2013 to 14 percent in 2015.
If a patient is considered at "low risk" for recurrence, does she still have to get endocrine therapy?
The second study tested a form of immunotherapy against chemo, in the most common lung cancer worldwide, known as non-small-cell lung cancer. The test looks for 21 specific genes associated with breast-cancer remission. The genetic testing gives cancer a "score" from 0 to 100. "Women with a higher recurrent score, there's some doubt about whether these results are fully implementable in the women under 50, just because it's a different hormone environment and they haven't yet gone through menopause and it may be that the chemotherapy helps to bring about a change in their hormone environment".
Doctors were unsure, however, whether women in the medium-risk range were benefiting from chemotherapy or just experiencing the side effects. Simply put, the side effects are awful: In addition to nausea, vomiting, hair and weight loss, chemo drugs can damage the heart and nervous system, and in rare cases, even cause different types of cancer. In the long term, it can cause early menopause, bone loss, chronic pain, kidney damage, and heart failure.
Professor Boyle said several immunotherapy trials for triple negative breast cancer are about to start in Australia.
The patients then went on to receive either hormonal therapy alone or the combo of hormonal therapy plus chemotherapy. It took place over the last ten years and followed over ten thousand women.
But experts caution that the treatment has only proved itself in one woman and that the clinical trials are needed to see how effective the therapy could be in other cancer patients.
After nine years, the study found that the two treatment groups had similar survival rates and freedom from disease recurrence. Oncotype DX costs around $4,000, which Medicare and many insurers cover.
The Institute of Cancer Research said: "This fascinating and exciting study in a single breast cancer patient provides a major "proof-of-principle" step forward, in showing how the power of the immune system can be harnessed to attack even the most difficult-to-treat cancer".
Thirty percent of the women in the trial did have evidence of cancer hiding in their bodies. These womenrandomly divided into two groups: One group received only hormone therapy after surgery, and the other group received both hormone therapy and chemotherapy.
"It also helps identify those women with this disease who really do benefit from the chemotherapy", he said.