Over 20% of Breast Cancer Patients Risk Recurrence by Not Taking Their Tamoxifen

SAN FRANCISCO—One in five women in a population-based study of breast cancer patients did not fill all her tamoxifen (Nolvadex) prescriptions during the first year of adjuvant tamoxifen therapy. The oldest and youngest patients and nonwhite patients were least likely to adhere to their tamoxifen regimens.

For the study, adherence was defined as filling prescriptions for 80% or more of the year covered and nonadherence as filling prescriptions for less than 80% of the year. "Seventy-seven percent of the women had greater than 80% of the year covered with filled tamoxifen prescriptions and were therefore classified as adherent. Twenty-three percent of the women were considered nonadherent because they had tamoxifen available to them less than 80% of the year," reported Ann Hart Partridge, MD, clinical fellow in medicine at Dana-Farber Cancer Institute in Boston. The study researchers were based at that institution and at Brigham and Women’s Hospital in Boston, although the study participants were residents of New Jersey.

The adherence rate was higher than the rates of 40% to 50% that have been observed for many chronic drug therapies, Dr. Partridge said.

Overall Adherence High

"The overall level of adherence with tamoxifen is high compared to other chronic medications," she said. "However, adherence is relatively low in absolute terms and compared to perception. Over one fourth of patients missed greater than 20% of doses and may be at risk for inadequate clinical response because of poor adherence."

Cancer patients were thought to have too much to lose to miss taking their tamoxifen, Dr. Partridge added, underscoring tamoxifen’s efficacy in preventing recurrence and death in women with early stage breast cancer. She urged greater efforts to ensure tamoxifen adherence, especially among nonwhite populations and patients who are younger than 45 or older than 85.

The study involved 2,378 women over the age of 18 who were enrolled in New Jersey’s Medicaid and Pharmaceutical Assistance to the Aged programs. Each filled a first prescription for tamoxifen between 1991 and 1995. The study traced whether the subsequent prescriptions filled by the women provided tamoxifen for all 365 days during the first year of treatment. Excluding women who had an identifiable reason to discontinue therapy—for example, breast cancer recurrence during the study year—did not change the adherence rates substantially.

Some Factors Ruled Out

The researchers ruled out socioeconomic status, use of estrogen replacement therapy, tumor staging, year of diagnosis, and other adjuvant therapies as factors in adherence, according to Dr. Partridge. "Women who had had a mastectomy were less adherent," she said, "and not being seen by an oncologist in the year prior to beginning tamoxifen therapy was also associated with poor adherence." She reported that 46% of the women had seen an oncologist in the year before receiving their first tamoxifen prescription, and 60% had undergone mastectomy.

The study was the largest to date on the use of tamoxifen or any oral antineoplastic agent outside of a clinical trial, according to Dr. Partridge. "Given the growing number of new effective oral agents for the treatment of cancer," she remarked, ‘‘attention to adherence is particularly important."