Adjuvant hormone therapy in breast cancer patients: Why do women stop treatment and what are the consequences?

Breast cancer is the most common cancer affecting women and many women are being treated to prevent the cancer from returning, for example with adjuvant hormone therapy. This therapy is prescribed as a once-a-day pill for estrogen receptor-positive breast cancer patients (around 80% of all cases) for a duration of at least five years.

Despite the fact that adjuvant hormone therapy benefits ER-positive breast cancer patients, many of them stop taking this medication before completing the recommended regimen, which can negatively impact their survival. Below, Erwei Zeng at the Department of Medical Epidemiology and Biostatistics discusses her doctoral thesis, in which she evaluated why this happens and how it affects patient outcomes in breast cancer patients diagnosed in the Stockholm-Gotland region of Sweden.

What are the most important results in your thesis?

One common side effect of adjuvant hormone therapy is hot flashes, which have been linked to better prognosis in a clinical trial, as these side effects suggest that the therapy is working for the patients. Our study showed that women with treatment-related hot flashes were more likely to have worse breast cancer prognoses, probably because they stopped taking the medication due to the negative side effects. Other reasons for stopping the medication prematurely included familial adversity, such as material deprivation, negative family dynamics, and bereavement.

We also found that breast cancer patients who stopped taking the medication were more likely to stop taking their cardiovascular medications, which might increase their risk of dying from not only breast cancer but also cardiovascular disease. On a positive note, we found that women who extended their adjuvant hormone therapy beyond a duration of five years had a better chance of staying cancer-free.

What do you think should be done for these women?

Breast cancer patients need to adhere to their recommended plan for adjuvant hormone therapy to maximize the chances of a positive outcome. Based on my projects, we have a few suggestions; First, patients need to be aware of potential side effects and talk to their doctors if they have concerns. Second, patients experiencing familial adversity may need additional support to complete the therapy. Third, taking multiple medications is challenging for breast cancer patients, requiring clinicians attention to help patients manage them. Finally, if recommended by their doctors, patients should consider extending the adjuvant hormone therapy duration after initial five years to improve their long-term survival.