A significant number of women who begin taking tamoxifen after initial breast cancer treatment stop taking the drug well before completing the usual 5-year course of therapy, according to a recent report in the journal CANCER. In a study of pharmacy records for 2,816 women with a new tamoxifen prescription, Irish researchers found that 22% stopped taking the drug within the first year of treatment, and 35% had quit by 3.5 years.
Quitting the drug early could put these women at higher risk of breast cancer recurrence, say Thomas I. Barron, MSc, and colleagues from Trinity College and St. James's Hospital in Dublin. Earlier studies have shown that women who take tamoxifen for the full 5 years are less likely to have their breast cancer return than women who take the drug for only 2 years.
The issue of not taking tamoxifen -- or any oral cancer therapy -- as directed is beginning to generate more interest and concern in the medical community, says Ann Partridge, MD, MPH, who has studied the topic extensively. The topic is often referred to as medication "adherence."
"People are just recognizing on a larger scale the impact of non-adherence," says Partridge, a medical oncologist at Dana-Farber Cancer Institute and an assistant professor at Harvard Medical School. "Conventionally, cancer therapy has been given in doctors' offices. But there's a burgeoning market of oral therapies where patients are taking more things outside the doctors' offices."
That makes it increasingly important to pinpoint and address the reasons patients fail to take their medications as prescribed or stop taking them altogether.
Because the Irish study looked only at prescription records and not diagnoses, medical records, or the patients themselves, the researchers could not fully explore why women stopped taking tamoxifen. The study did exclude women who began a different hormonal therapy within 6 months of stopping tamoxifen. But it could not identify the women who may have quit because of a breast cancer recurrence or new cancer, or because the side effects of tamoxifen were too bothersome.
Women between the ages of 35 and 44 and those over age 75 were most likely to quit tamoxifen. Women who had used antidepressants in the year before starting tamoxifen were also more likely to quit.
Those findings offer some clues, Barron and his colleagues say. Perhaps older women are more likely to have conditions like dementia that make them forget their medication. Younger women may be less willing to accept the menopause-like side effects the drug can cause. But more research is needed to really understand what causes women to stray from their treatment plan, says Partridge.
"There are lots of reasons people don't take their drugs, some of which are modifiable," she explains.
For instance, people who often forget their medication may benefit from pill diaries or pill boxes to help them keep track of dosages, Partridge points out. Scheduling refills to coincide with other regular activities (monthly bill-paying, quarterly oil changes) is another suggestion she offers patients. Refill reminders from pharmacies and insurance companies can also help women stick with their medication. Financial assistance programs from drug companies and other sources can help women who otherwise might not be able to afford their full course of treatment.
Side effects are another area where action can be taken, Partridge says. Hot flashes may be helped by vitamin E or SSRI antidepressants. Bone and muscle pain can be addressed with NSAID pain relievers such as aspirin or ibuprofen. Over-the-counter remedies can help with vaginal dryness.
But patients and doctors need to talk about these issues if they hope to address them, Partridge says.
"The most important thing is to discuss with your doctor what's going on and ask about interventions," she advises.
Doctors should also make a point of asking patients how they're handling their medication schedule and any possible side effects, she adds.
Citation: "Early Discontinuation of Tamoxifen." Published online Jan. 22, 2007, in Cancer. First author: Thomas I. Barron, MSc, Trinity College Dublin, Ireland.
