Most breast cancers are not inherited. What doctors want women to understand

After decades of progress against breast cancer, two statistics tell much of the story, even if many patients never hear them. In the 1970s, five-year survival was in the 70% range, said Dr. Alberto Montero, a medical oncologist, associate professor of medicine at the Case Western Reserve University School of Medicine, and clinical director of the Breast Cancer Medical Oncology Program at University Hospitals Seidman Cancer Center. Today, he said, it is above 95%, and early detection is a major reason why.

Montero said the main message is simple: breast cancer is now highly treatable, and finding it early makes a major difference. Mammography can detect small tumors, and outcomes are closely tied to how early the disease is found.

The National Cancer Institute's SEER program reports a five-year relative survival rate of 91.9% for women diagnosed with breast cancer in recent years, compared with about 76% for women diagnosed in the mid-1970s. Survival depends heavily on how far the cancer has spread. Roughly 64% of cases are found while the disease is still limited to the breast, and the five-year relative survival rate for that group is 100%, meaning those women are, on average, as likely to be alive five years later as women who never had the disease.

Based on an interview with Montero, this article from Case Western Reserve University School of Medicine looks at what screening guidelines actually cover, why most breast cancers are not linked to inherited mutations, and how molecular testing is helping doctors decide who can avoid chemotherapy.

What the screening guidelines actually cover

Mammography remains the standard test, Montero said, against which other approaches are measured. “It’s still the gold standard,” he said. Under current guidance, the baseline mammogram is recommended at about age 40.

He also emphasized a point that is often overlooked: those guidelines apply to women at average risk. Someone with a strong family history or a known genetic mutation follows a different pathway, and a physician can help determine that person's true level of risk.

In recent years, major medical groups have converged on age 40 as the starting point, though they still differ on how often screening should be done.

Breast cancer is not one disease

“Breast cancer is indeed not just one kind of cancer,” Montero said. “I think that’s another thing that a lot of people may not understand.” Advances in science and molecular testing, he said, have shown that breast cancer includes at least four subtypes, each with different treatment approaches and its own pattern of progression.

Researchers generally describe those subtypes as luminal A, luminal B, HER2-enriched and basal-like, with the last group overlapping heavily with triple-negative breast cancer, according to Susan G. Komen. The group notes that treatment decisions are driven mostly by stage, grade, hormone receptor status and HER2 status rather than by the subtype label alone, even though the categories often align in practice.

Genetics explains less than many people think

When asked who should be tested for inherited risk, Montero began by reframing the issue. “The important thing to know is that 90% of women who have breast cancer don't have a genetic cause,” he said.

Inherited cases make up only a small portion of all diagnoses. About 5% to 10% of breast cancers are tied to inherited gene mutations, most commonly BRCA1 and BRCA2. Carrying one of these mutations matters greatly for the person who has it. According to the National Cancer Institute, more than 60% of women with a harmful BRCA1 or BRCA2 change develop breast cancer during their lifetime, compared with about 13% of women in the general population. Testing guidance has expanded accordingly. A 2024 guideline from the American Society of Clinical Oncology and the Society of Surgical Oncology recommends offering BRCA1/2 testing to every newly diagnosed patient age 65 or younger, and to selected patients older than 65 based on family history, ancestry, tumor type or eligibility for certain drugs.

How doctors decide who can skip chemotherapy

The same molecular tools used to classify breast cancer are now helping doctors decide how aggressively to treat it. “Before, we used to give chemo to almost any patient who had a tumor above a certain size,” Montero said. “Now we can do genetic testing, and we can understand who has a higher risk cancer or a lower risk cancer and who needs chemotherapy, who doesn't need chemotherapy.”

The evidence for that change came from TAILORx, a trial involving 10,273 women with hormone-receptor-positive, HER2-negative, node-negative breast cancer. Researchers used a 21-gene assay to score each tumor. Among the 9,719 participants with follow-up data, 69% fell in the middle range, and for those women, hormone therapy alone performed as well as hormone therapy combined with chemotherapy, though chemotherapy still appeared to help women age 50 and younger. The study, the largest breast cancer treatment trial up to that point, was published in the New England Journal of Medicine in 2018.

Montero said that is where the field is heading. “There's a lot of progress in being able to personalize a treatment for patients so that they get only the treatments that they need,” he said, “and they avoid any toxic treatments that they might not need.”