AT SABCS 2016

SAN ANTONIO (FRONTLINE MEDICAL NEWS) – When does adjuvant therapy with an aromatase inhibitor become too much of a good thing? Or to put it another way, what’s the optimal duration of extended aromatase inhibitor therapy? That’s the question that three clinical trials have tried – but largely failed – to answer.

For example, the randomized, double-blinded NSABP B-42 trial, comparing extended therapy with letrozole (Femara) in postmenopausal women with hormone receptor–positive (HR+) breast cancer who have completed previous adjuvant therapy with an aromatase inhibitor (AI) showed no difference in disease-free survival (DFS) after 7 years of follow-up between women treated with extended letrozole or placebo.

“Our findings suggest that careful assessment of potential risks and benefits is required before recommending extended letrozole therapy to patients with early-stage breast cancer, including patient and tumor characteristics such as age and nodal status, existing comorbidities, information on bone mineral density, and tolerance of the aromatase inhibitor in the initial years,” Eleftherios P. Mamounas, MD of NRG Oncology/NSABP, said at the San Antonio Breast Cancer Symposium.

DATA data

In the DATA study , also presented here, investigators from the Netherlands compared 6 years of anastrozole (Arimidex) to 3 years of anastrozole following 2 or 3 years of adjuvant tamoxifen for postmenopausal women with estrogen receptor–positive (ER+), and/or progesterone receptor–positive (PR+) breast cancer.

They found that “adapted” DFS (DFS starting 3 years after randomization) and adapted overall survival (OS) were similar between the two groups.

“The findings of the DATA study do not support extended adjuvant AI use after 5 years of sequential endocrine therapy for all postmenopausal hormone receptor–positive breast cancer patients,” said Vivianne Tjan-Heijnen, MD, of Maastricht University Medical Center in the Netherlands.

Less than ideal

In the optimistically named IDEAL trial, a separate team of investigators, also from the Netherlands, looked at the relative merits of continuing adjuvant therapy with letrozole for 2.5 or 5 years following 5 years of adjuvant therapy with tamoxifen, an AI, or a combination in postmenopausal women with HR+ breast cancer.

They found no differences in either DFS or OS between patients treated for 5 years or those treated for only half that long.

“We conclude that there is no benefit of extending AI-based therapy longer than two-and-a-half years,” said Erik Blok, MD, of Leiden University Medical Center in the Netherlands.

Give what to whom for how long?

Results of the trials raise more questions than they answer, said Michael Gnant, MD, of the Medical University of Vienna, the invited discussant.

“Essentially, these three trials did not reach the necessary statistical significance levels to demonstrate a clear benefit for the respective AI extension,” he said.

“Can other agents we use in luminal breast cancer help? Frankly, I don’t think so. Based on their tolerability profile, and in part also on financial toxicity, I don’t think that the promising agents we explore in many situations for the treatment of hormone receptor–positive breast cancer will realistically be used in the extended adjuvant setting,” he said.

What’s needed, he said, are new strategies for targeting the chronic part of luminal breast cancer recurrence risk. Using endocrine therapies in this setting will likely be ineffective. Instead, agents that could directly target dormant cancer stem cells would “eliminate the source of late metastases for good.”

The best evidence to date clearly points to individualized treatment plans for patients, Dr. Gnant said.

For example, for a patient who has had 2-5 years of tamoxifen, an AI for 2.5-5 additional years can help to prevent recurrences, provided that the patient has risk factors for recurrence and excellent bone health.

“Based on the trial results, it is more complex for a patient who comes off initial or sequential AI. There are factors favoring the extension of AI treatment, and other factors to speak against such extension. I suggest to start with patient features at this time,” he said.

Currently, the main factor driving the choice of extended AI therapy will be how well the patient has tolerated AIs in the first years of therapy and whether she is at increased risk for fractures, suggesting younger age as a factor favoring extended AI use.

Patients with higher clinicopathologic risk factors such as node positivity or more luminal type tumors, as well as higher risk according to genomic studies, might also benefit from extended AI therapy, he said.

Biomarkers needed

“What the data from these and other trials tell us is that endocrine therapy is not for everyone. We need biomarkers that can tell us who should be getting extended endocrine therapy, be it 10 years or even a longer duration of time, versus a subgroup that might do very well with 5 five years of AI,” Aditya Bardia, MBBS, MPH, of the breast cancer division at Massachusetts General Hospital Cancer Center in Boston, said in an interview.

There are several such biomarkers under investigation, but they need validation and testing in large scale clinical trials before they find their way into day-to-practice, he said.

Dr. Bardia was not involved in the studies.

NSABP B-42 was sponsored by PrECOG with financial support from Novartis. Dr. Mamounas reported having no conflicts of interest. The DATA trial was sponsored by the Dutch Breast Cancer Research Group and Novartis. Dr. Tjan-Heijnen reported nothing to disclose. IDEAL was supported by the Dutch Breast Cancer Research Group and Novartis. Dr. Blok reported nothing to disclose.

op@frontlinemedcom.com

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