Phyllis Laccetti, a participant in the TAILORx breast cancer study, is pictured outside her home in Ossining, N.Y. (Eva Deitch for The Washington Post)

One of the big questions facing women with early-stage breast cancer is whether to be treated with chemotherapy to reduce their risks that the cancer will return. A new study presented Sunday at the annual meeting of the American Society of Clinical Oncology provides much-needed clarity: Most of these women can safely skip chemo.

Although chemotherapy for early-stage breast cancer has been declining, physicians said the latest research findings will have a major effect by either giving patients more confidence in their decisions or encouraging them to take a different treatment approach. There are some important nuances, however. Here’s a rundown:

What did the study show? 

The decade-long study, called TAILORx, involved the most common type of breast cancer — one that is driven by hormones, has not spread to the lymph nodes and does not contain a protein called HER2. Previously, the same study had shown that women with a low risk of recurrence can avoid chemo, and other studies had shown that those with a high risk of recurrence should receive it.

So the biggest questions involved women in the intermediate-risk category: Did chemo reduce their chance of recurrence? Or was it sufficient for them to be treated only with endocrine therapy, which blocks the cancer-spurring properties of hormones?

After years of waiting, doctors and patients finally got the answer. Women older than 50 with a midrange risk — defined in the study as a score of 11 to 25 on a tumor test — can skip chemo and just have endocrine therapy. Women 50 or younger can avoid chemo if their scores are lower than 16, said lead author Joseph Sparano, associate director for clinical research at the Albert Einstein Cancer Center in New York. (Women in the younger-age category who have higher scores still should consider chemo.)

All told, about 70 percent of women with this particular cancer — meaning more than 85,000 women a year in the United States — can safely forgo chemotherapy, the experts concluded.

How do doctors and patients know if a patient is high-risk?

The researchers who conducted the trial, which was the biggest breast-cancer treatment trial ever, used a gene test called Oncotype DX to gauge recurrence risk. Determining such risk is critical in deciding treatment, because when breast cancer spreads to other parts of the body it’s generally considered incurable. The test, which has been on the market for several years, analyzes the activity of 21 genes to predict a woman’s risk of recurrence over 10 years.

Many doctors have been using that test or similar ones for years. The new study provides the highest level of proof that the assay is an accurate tool and thus reduces uncertainty for the intermediate group,  said Dawn Hershman, a breast oncologist at NewYork-Presbyterian Columbia University Medical Center.

If a patient is considered at “low risk” for recurrence, does she still have to get endocrine therapy?

Yes, and several doctors at the ASCO meeting stressed this point. Endocrine therapy, such as tamoxifen, is more important with this disease than chemotherapy, said Otis Brawley, chief medical and scientific officer for the American Cancer Society.

Sparano noted that given the several variations of endocrine therapy available, women who have trouble tolerating one should try another.

“It’s important to stay on it,” he said.

How does the study fit into the debate over “de-escalating” treatment of early-stage breast cancer?

It provides important information on a safe way to cut back treatment, an issue that has prompted vigorous debate not only for breast cancer but also for other malignancies.

In the early 2000s, Sparano recalled, the National Cancer Institute recommended that most women be offered chemo. But as doctors began to learn more about the disease, experts decided that many patients were being over-treated.

In recent years, many doctors have reduced their use of chemo, which can cause nausea, fatigue and, in rare cases, more serious complications such as leukemia and heart failure. Oncotype DX and other genomic tests have spurred a trend sure to accelerate following Sunday’s report.

Sparano acknowledged that the trial took a long time but said it was worth the wait. “If we are going to take a step back” from chemotherapy, he said, “we really had to be sure.”

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