A high percentage of younger, premenopausal women being treated for early-stage breast cancer do not continue to use tamoxifen, a hormonal therapy, within the first year of treatment, despite being advised to use it for at least five years, a French study reports.
The study, “Serum assessment of non-adherence to adjuvant endocrine therapy (ET) among premenopausal patients in the prospective multicenter CANTO cohort,” was presented at the European Society for Medical Oncology (ESMO) 2018 Congress, in Munich last month.
Most breast cancers are HR-positive, meaning they depend on hormones, like estrogen, to continue growing. These cancers are generally treated with hormone therapies, like tamoxifen, that prevent estrogen from interacting with its receptor, thus reducing growth signals to the tumors.
The recommended period for hormonal therapy ranges between five and 10 years, but studies suggest that many patients — particularly younger, premenopausal ones — fail to adhere to long-term treatment.
Inadequate treatment increases the risk of cancer relapse and metastatic disease. Researchers aimed to assess the proportion of premenopausal breast cancer patients who stopped long-term treatment with tamoxifen.
Women in this study had taken part in the CANTO trial (NCT01993498), a large French evaluation of the long-term impact of treatment toxicity in breast cancer patients.
Researchers focused on a sub-group of 1,799 premenopausal women recently diagnosed with early stage breast cancer (non-metastatic), who were prescribed adjuvant (add-on) hormone therapy — treatment given after surgery, chemotherapy and/or radiation therapy to prevent a cancer from returning.
Many studies have addressed adherence to treatment in breast cancer patients, but they usually rely solely on patients’ self-reports of adherence. Now, researchers sought to examine compliance with treatment guidelines by measuring tamoxifen blood levels at one, three, and five years.
Data presented at ESMO covered the first year of treatment, and showed that among the 1,177 premenopausal women who reached the first-year follow up, nearly one-fifth (16%) were not adequately adherent, and 10.7% were considered non-adherent — without detectable levels of tamoxifen in blood circulation.
“I was surprised at the high rate of non-adherence, which was considerably higher than reported previously,” Barbara Pistilli, a medical oncologist at Institut Gustave Roussy, and the study’s lead author, said in a press release.
At least half of those with low or no low or no detectable tamoxifen levels did not report a failure to take tamoxifen as prescribed. The study is continuing to assess patients at three and five years, and researchers are also trying to understand why some patients stop taking tamoxifen, and to develop interventions that increase adherence.
“We should take time to explore with patients if they are experiencing side-effects that can affect their adherence, and support them to be open about non-adherence so that we can discuss options to help,” Pistilli said.