Chemotherapy gets a bad rap for side effects, even if that reputation is sometimes exaggerated or outdated. Still, chemo is hardly fun. That’s why growing evidence that some women who would have been slated for chemo in the past may not benefit from it—and, therefore, don’t need it—comes as welcome news.

The era of “one-size-fits-all” therapy is ending, explains Anne Moore, MD, professor of clinical medicine and medical director of breast oncology at the Weill Cornell Medical College in New York City. That, she says, is because experts have increasingly observed that tumors with particular features respond differently to different treatments.

After you’re diagnosed with breast cancer, your doctor will order a hormone receptor assay—a test to see whether your cancer is estrogen receptor (ER)-positive, meaning that its growth is fueled by the female hormone estrogen. Breast cancers that are ER-positive usually respond well to the hormonal therapy tamoxifen and may get little additional benefit from chemotherapy. In contrast, women whose cancers are estrogen receptor (ER)-negative tend to benefit more from chemo.

“Doctors want to give chemo where it works, and don’t want to give it where it doesn’t,” says Clifford Hudis, MD, Chief of the Breast Cancer Medicine Service at Memorial Sloan-Kettering Cancer Center
in New York.

But hormone receptor status isn’t the only deciding factor. Age, lymph node involvement, and the size and grade (degree of cell abnormality) of the cancer are also important in determining whether or not a woman should undergo chemo.

Sometimes, says Dr. Moore, the decision on whether to give a woman chemo isn’t clear-cut. “The women with whom we have the biggest problem deciding” whether or not to offer chemotherapy, “are those who are ER-positive and have negative lymph nodes.” In general, she adds, those women are at less risk for recurrence than are women with positive lymph nodes, and may do well on hormone therapy alone.

However, she adds, “Even with as little as a 3% benefit, oncologists will discuss chemo seriously. Women with young children may grab any chance to decrease their risk of recurrence. Older women, on the other hand, may not feel a small benefit is worth it.”

What’s the bottom line for patients? Dr. Moore says it’s crucial that you understand exactly what your doctor is suggesting in terms of treatment and why. “And the explanation must be specific to you,” she insists, “not just for breast cancer patients in general.”