Patients with tumors under 0.5 cm have not been widely offered this treatment previously

BUFFALO, N.Y. — Many people diagnosed with breast cancers that are small but invasive could benefit from hormone treatment, a new study led by physicians at Roswell Park Comprehensive Cancer Center confirms. Their findings were published today in the journal JAMA Network Open.

Previously, patients with some small but potentially dangerous breast tumors — specifically, hormone receptor-positive, human epidermal growth factor receptor (HER) 2-negative breast cancer tumors measuring between 0.1 and 0.5 cm — were not included in studies on the efficacy of hormone therapy, says Anurag Singh, MD, Professor of Oncology and Director of Radiation Research in the Department of Radiation Medicine at Roswell Park.

With nearly one in five women with breast cancer falling into this category of having a small but invasive breast tumor, they were previously under-represented in research into the efficacy of hormone therapy, also known as endocrine therapy, with either tamoxifen or with an aromatase inhibitor.

The team, led by Dr. Singh, analyzed data on 42,708 patients from the National Cancer Database who were diagnosed with small, T1a breast tumors (larger than 0.1 cm, but no larger than 0.5 cm) between January 2010 and December 2015. The group included more than 31,500 patients who had received endocrine therapy and another nearly 11,200 who had not.

The team reports that among patients who had received hormone therapy, overall survival was better than in those who did not, and the addition of hormone therapy was shown to generally be effective.

The risk of relapse from these very small tumors remains significant enough to lend weight to a recommendation of hormone therapy in addition to radiation, the authors note. Hormone therapy also did not negatively impact any other treatment the patient was exposed to at the same time.

“Those patients who may benefit from hormone therapy should be given clear information about this possible course of treatment — and about its potential long-term toxicities,” says Dr. Singh, who is senior author on the new publication. “The side effects of endocrine treatments can impact quality of life significantly, sometimes for several years, so they’re not the right option for everyone.”

The team believes this is the largest study to evaluate the overall survival rate of endocrine therapy for small, invasive breast cancer tumors using a national registry database.

The researchers included Sung Jun Ma, MD, of Roswell Park, and Oluwadamilola Oladeru, MD, of Massachusetts General Hospital, co-first authors on the new publication.

The new study builds on recent work from this same team showing that endocrine therapy can be beneficial in other breast cancer subtypes — HR-positive, HER-2 negative, pT1-2N0, non-high-grade breast cancer with favorable histologies, including tubular, mucinous and cribriform tumors.