After surgery, some cancer patients can safely skip radiation or chemotherapy, according to two studies exploring shorter, gentler cancer care.

Researchers are looking for ways to precisely predict which cancer patients can avoid unneeded treatment to cut down on harmful side effects and unnecessary costs.

One new study used a blood test to determine which colon cancer patients could skip chemotherapy after surgery. Another suggests some low-risk breast cancer patients can omit radiation after lumpectomy.

The research was discussed at the annual meeting of the American Society of Clinical Oncology, which wrapped up Tuesday in Chicago. The colon cancer study, funded by the Australian and U.S. governments and nonprofit groups, was published Saturday by the New England Journal of Medicine.

The findings could allow doctors to “focus on the patients we think would truly benefit from chemotherapy and avoid the side effects for patients for whom it’s likely unnecessary,” said Dr. Stacey Cohen of Fred Hutchinson Cancer Center in Seattle, who reviewed the colon cancer findings and was not involved in the research.

COLON CANCER

Many colon cancer patients are given chemotherapy after surgery, even though they may be cured. The drugs can come with side effects such as nausea, anemia and memory problems.

But pinpointing which patients might not need further treatment has been tricky. Scientists studied whether a blood test could help doctors make the call.

The study involved 455 patients who had surgery because cancer had spread into the colon wall. After surgery, one group received a blood test, customized to their tumor’s genetic profile, to detect any remaining bits of cancer DNA.

Their care was guided by the blood test: If it showed no signs of remaining cancer, the patients did not get chemotherapy. Meanwhile, doctors made chemo decisions for the rest of the patients in the usual way, guided by analysis of the tumor and nearby tissue.

Fewer patients in the blood test group got chemo — 15% vs. 28%. But about 93% of both groups were still free of cancer after two years. In other words, the blood test group fared equally well with less chemotherapy.

“In patients where cancer DNA is not detected after surgery, the chance of cancer relapse is very low, suggesting that chemotherapy is very unlikely to benefit these patients,” said Dr. Jeanne Tie of the Peter MacCallum Cancer Centre in Melbourne, Australia, who led the research.

Skipping chemo makes “a big difference in a person’s quality of life if that can be done without having to put them at jeopardy for recurrence,” said ASCO president Dr. Everett Vokes, who specializes in head and neck and lung cancer at University of Chicago Medicine.

BREAST CANCER

The other study followed 500 older women with a common form of early-stage breast cancer and low levels of a protein known as Ki67, a marker for fast-growing cancer.

After surgery, the women took hormone-blocking pills, a standard treatment for this type of cancer, but they did not get radiation treatment.

After five years, 10 of the women saw cancer return in the same breast, and there was one breast cancer death. There was no comparison group, but researchers said the results compare favorably to historical data for similar patients who had radiation.

“We estimate the benefits of radiation would be very small in this population compared to the side effects,” said Dr. Timothy Whelan of McMaster University in Hamilton, Ontario, who led the study, which was supported by the Canadian Breast Cancer Foundation and the Canadian Cancer Society.

Radiation can cause skin problems, fatigue and, less commonly, long-term heart problems and second cancers.

The study is a “feel-good” message for patients with low-risk tumors and will help doctors understand which of their patients they “can comfortably, with confidence” omit radiation, said Dr. Deborah Axelrod of NYU Langone Health, who was not involved in the research.

(AP)