Breast Cancer Index Identifies Patients Who Will Benefit From Extended Endocrine Therapy, Data Shows

Biotheranostics‘ Breast Cancer Index can help distinguish which breast cancer patients will derive a benefit from prolonged endocrine therapy — allowing those who don’t to stop treatment and avoid its unpleasant side effects, new data suggests.

The findings were shared at the 2019 American Society of Clinical Oncology (ASCO) Annual Meeting, held recently in Chicago, in a presentation titled, “Trans-aTTom: Breast Cancer Index for prediction of endocrine benefit and late distant recurrence (DR) in patients with HR breast cancer treated in the adjuvant tamoxifen—To offer more? (aTTom) trial.”

Endocrine therapy starves tumors of the hormones, primarily estrogen, that drive cancer cell growth. For people with hormone receptor (HR)-positive breast cancer, it can be lifesaving. However, endocrine therapy also can cause a number of unpleasant side effects, including osteoporosis, joint pain, blood clots, and endometrial cancer.

This has led to a dilemma over how long endocrine therapy should be given — for five or 10 years?

The Breast Cancer Index (BCI), a test that measures gene expression in the tumor, is intended to solve this problem by identifying those patients who will benefit from the additional five years of treatment. That would allow clinicians to stop treatment — and avoid the negative side effects — in women who won’t benefit from prolonged therapy.

To validate the accuracy of BCI, researchers examined data from participants treated in the prospective aTTom Phase 3 trial (NCT00003678). That trial included 6,953 women with HR-positive breast cancer who had completed at least four years of endocrine therapy with tamoxifen, a drug that blocks the estrogen receptor. Participants were randomly selected to either stop tamoxifen treatment or to continue therapy for five more years.

At the meeting, researchers presented data from 583 patients who were node-positive, meaning some cancer cells had already spread from the breast to nearby lymph nodes.

The BCI divided these patients into two groups, termed H/I-High (287 people) and H/I-Low (296 women). The term “H/I” is derived from the particular genes measured by the BCI — HoxB13 and IL17BR.

After a median of 12 years of follow-up, researchers measured the recurrence-free interval (RFI) in both groups. RFI is the time in which there is no evidence of the cancer regrowing in the breast or elsewhere.

In the H/I-Low group, there was no significant difference in RFI between individuals treated with tamoxifen for five or 10 years. However, in the H/I-High group, there was a 10.2% benefit in RFI among those who were treated for 10 years, as compared with five years.

“Results from the Trans-aTTom study add to the growing body of evidence that BCI accurately identifies which early-stage HR patients are associated with better outcomes and preferential response to extended endocrine therapy,” Catherine Schnabel, PhD, the chief scientific officer of Biotheranostics, said in a press release. “Clinicians may use BCI to personalize their approach and provide validated genomic information to help patients weigh the risks and benefits of prolonging their endocrine treatment.”

The researchers said the BCI will help in individual treatment planning.

“[I]dentifying women for whom extending endocrine therapy helps reduce their risk of recurrence is important to help decrease their anxiety, increase their satisfaction and comfort with their treatment decision, and potentially enable them to comply effectively with their treatment plan,” they said.