Researchers are getting closer to identifying women who can safely skip chemotherapy as a treatment for breast cancer.

Some women with early stage breast cancer are at such low risk for recurrence that chemotherapy is unnecessary.

For others, chemotherapy is a lifesaving treatment.

For the most part, doctors can’t predict which patients are which. But we may be on the verge of a major change.

Early stage breast cancer usually means stage 1 and stage 2. In these stages cancers haven’t spread beyond the breast or nearby lymph nodes. Treatment usually starts with surgery and may be followed by hormone therapy or radiation.

For many women with early stage breast cancer, treatment will also include chemotherapy. The powerful drugs used are designed to kill fast-growing cells throughout the body. That takes care of cancer cells, but also destroys some healthy cells.

That’s why chemotherapy drugs cause hair loss and susceptibility to opportunistic infections.

Side effects can also include fatigue, nausea, and weight loss. In the long term, chemotherapy can impact fertility, harm organs, and increase the risk of developing other cancers.

Thousands of breast cancer patients could avoid all that if they knew their risk of recurrence.

That’s where genomic testing comes in.

Read more: Breast cancer genome could lead to personalized treatments »

A randomized study of 6,693 breast cancer patients from nine European countries shows the promise of genomic testing.

Details of the study were published in The New England Journal of Medicine.

All the women in the study had early stage breast cancer. To determine their genomic risk of recurrence, researchers used the 70-gene signature test called MammaPrint.

Clinical risk was also considered, which involves factors such as tumor size, grade, and lymph node involvement.

Of the group, 1,550 patients were found to be at high clinical risk but low genomic risk. Some had chemotherapy and some did not.

Among those who did not have chemotherapy, the five-year survival rate without distant metastasis was 94 percent. For those who did have chemotherapy, the rate was 1.5 percent higher.

Study authors concluded that about 46 percent of women with breast cancer who are at high clinical risk of recurrence may not need chemotherapy.

An editorial that accompanied the study said genomic testing can identify situations where a specific intervention is not effective.

The editorial, written by Dr. Clifford A. Hudis and Dr. Maura Dickler, went on to say, “A difference of 1.5 percentage points, if real, might mean more to one patient than to another. Thus, the stated difference does not precisely exclude a benefit that clinicians and patients might find meaningful.”

“This study is a big deal,” said Dr. Timothy Byun, a medical oncologist with The Center for Cancer Prevention and Treatment at St. Joseph Hospital in Southern California, who was not involved in the study.

In an interview with Healthline, Byun said the study may result in fewer breast cancer patients getting chemotherapy, at least in European countries.

“In the United States, many of us have already been using the Oncotype DX test to help guide our decisions,” said Byun. “It uses a 21-gene score. It gives similar information, but we don’t know if there’s a 100 percent correlation with the MammaPrint test.”

Byun referred to the recent TAILORx Trial using the 21-gene test. It found that low-risk patients did well without chemotherapy.

That study showed the test could select a cohort of patients with a 99 percent chance of five-year survival without distant metastasis. For those women, the risks of chemotherapy aren’t justifiable.

Researchers are still waiting for this data to mature, cautions Byun.

“We know that when oncologists see patients after surgery, we look at traditional clinical indicators to guide our decision-making process as to benefits and harms of chemotherapy,” he said.

With the information currently available, it’s likely that some breast cancer patients get unnecessary chemotherapy.

“The crux of the European study is they wanted to see if genomic study could give a more precise answer as to who really needs treatment and who doesn’t,” said Byun. “Those who don’t could avoid chemotherapy, which is toxic to many patients.”

There’s a caveat, according to Byun. Genomic studies, for the most part, have included only estrogen-receptor positive breast cancer patients.

“The European study did include some patients who were estrogen-receptor negative, HER2-positive, and triple-negative. But since the number was relatively small, it’s not clear if we should be using this information for all patients,” he said.

Referring to the 1.5 percent difference in metastasis-free survival in favor of chemotherapy, Byun said, “It’s a small difference, but it makes us wonder if there’s some benefit to chemotherapy in that population.

“When we look at the survival curve, decade after decade, more women than ever are surviving breast cancer because of adjuvant chemotherapy,” he added. “Yes, there’s an overtreatment, but the population as a whole is benefiting from it. “

Byun said overtreatment is not unique to breast cancer.

“We have the same problem with lung and colon cancers. It would be nice if we could have this kind of tool to guide clinicians to fine tune who does and doesn’t need therapy for lung, colon, and other cancers. There is an Oncotype DX for colon cancer, but it doesn’t have that type of predictive power.”

Read more: Everything you need to know about the Oncotype DX test »

Byun said genomic testing is still far off from becoming mainstream.

“The field is moving toward more precision medicine and moving away from traditional chemotherapy. Having said that, chemotherapy is still going to play a role, but it will become more selective. More will be spared from unnecessary chemotherapy. More people who need it will get it,” he said.

“Instead of treating 100 people to benefit two or three, we could do a much better job of figuring out who would benefit,” Byun explained.

“This study was a major effort by our European colleagues and they ought to be applauded. The study does show that the use of genomic information can help some patients avoid chemotherapy. That’s all positive information,” he said.

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