LOW ADHERENCE FOR HORMONAL THERAPY IN BREAST CANCER

June 30, 2010 — Only half of the women with early-stage breast cancer who were prescribed tamoxifen and/or aromatase inhibitors completed the full course of treatment, putting themselves at increased risk for breast cancer recurrence.

The new finding comes from a study of 8769 patients in the Kaiser Permanente of Northern California healthcare system, published online June 28 in the Journal of Clinical Oncology.

Over the 4.5 year follow -period, 30% of women discontinued therapy. Of those who continued, 28% were nonadherent.

Hence, overall, only 49% were fully adherent for the entire 4.5 years.

Discontinuation rates were similar for women taking tamoxifen alone and aromatase inhibitors alone, although women who took a combination of the 2 were less likely to stop early, the researchers note.

The study was carried out from 1996 to 2007; 43% of patients were prescribed tamoxifen alone, 26% aromatase inhibitors alone, and 30% a combination of the 2.

Highest Rates in Youngest Patients

The highest rate of discontinuation (32%) was seen in women younger than 40 years of age.

"We were surprised to see that so many young women stopped treatment early, despite the fact that the therapy has a proven track record in reducing breast cancer recurrence," lead researcher Dawn Hershman, MD, associate professor of medicine and epidemiology at Columbia University Medical Center in New York City, said in a press release.

"It's very disturbing that patients under 40 had the highest discontinuation and nonadherence rates, because those patients have the longest life expectancy," she added.

Two previous studied of tamoxifen also found younger age to be a predictor of early discontinuation, the researchers note, and suggest that "young adults with cancer may be a particularly vulnerable group."

Consistent With Previous Results

"Our results are consistent with other studies that have shown high discontinuation and nonadherence rates among women on adjuvant hormonal therapy," the researchers write. Despite differences in methodology, previous studies have all consistently reported discontinuation rates in the range of 30% to 50%.

One reason for the high rate of discontinuation might be toxicity, the researchers suggest. They cite a previous study of 622 postmenopausal women, which found a 30% discontinuation rate for aromatase inhibitors, in which 84% of those who discontinued said they did so because of adverse effects (Breast Cancer Res Treat. 2007;106[Suppl 1]:abstract 3131).

"We found that 4% of patients filled only 1 prescription for their hormonal therapy," Dr. Hershman and colleagues note, adding that early treatment toxicities might be the cause.

"We found that 13% of patients who continued hormonal therapy were nonadherent from the first refill," they also note, and suggest that "it might be helpful to identify interventions to improve adherence at this time point."

Another point the researchers emphasize is that "adherence to hormonal therapy is highly dependent on communication between the physician and the patient."

Understanding Noncompliance Is Important

Understanding why patients don't take their medicines as directed is becoming increasing important in the cancer field, as more treatment is moving out of the clinic and into the home, said Jennifer Obel, MD, attending physician at NorthShore University Health System in Evanston, Illinois, and a member of the American Society of Clinical Oncology Communications Committee.

"We now have more than 50 oral anticancer medications," Dr. Obel notes.

"This new study reaffirms some worrisome trends for women completing hormonal therapy, and brings up the larger issue of noncompliance for cancer therapies in general," she said in a statement.

A recent British study found noncompliance with imatinib (Gleevec) in the treatment of chronic myeloid leukemia in 25% of patients, putting those patients at risk for poorer outcomes. Those researchers expressed surprise at this rate of nonadherence among cancer patients, although it is similar to that seen with other chronic diseases. "You would think that cancer patients would be more motivated to keep taking their drug, so the finding is rather counterintuitive," said Nick Barber, PhD, professor of practice and policy at the School of Pharmacy, London.

Dr. Hershman and colleagues echo this sentiment, and say it is surprising that nonadherence appears to be almost as significant a problem in oncology, with potentially life-saving medications, as it is in other disease areas.

Dr. Hershman and colleagues have disclosed no relevant financial relationships.

J Clin Oncol. Published online July 28, 2010. Abstract