SAN ANTONIO – Hypertension, dyslipidemia, and type 2 diabetes are common among breast cancer survivors – and so is nonadherence to medications prescribed for these major comorbid conditions.
That was the central finding from COMBO (Commonly Used Medications and Breast Cancer Outcomes), a retrospective cohort study of 4,216 breast cancer survivors belonging to Group Health Cooperative, Gregory S. Calip, Pharm.D., reported at the San Antonio Breast Cancer Symposium.
Gregory S. Calip, Pharm.D.
“This is the first study to investigate breast cancer characteristics and treatments in relation to nonadherence to chronic medications for hypertension, diabetes, and dyslipidemia,” said Dr. Calip of the University of Illinois, Chicago. “Our results suggest that some breast cancer treatments may be associated with nonadherence to antihypertensive agents and oral diabetes medications, but not statins. These findings highlight possible opportunities to improve comorbid condition care in the growing population of breast cancer survivors.”
The irony is that while experiencing breast cancer understandably renders survivors deeply concerned about the prospect of cancer-related death, by not taking their medications for these common comorbid conditions these women increase their overall mortality risk, and particularly their risk of death due to cardiovascular disease and stroke.
The women in the COMBO study had been diagnosed with stage I or II breast cancer during 1990-2008 and did not experience recurrence or a second primary breast cancer during their second year after breast cancer diagnosis. Their medication adherence during that second year was measured via automated health plan pharmacy dispensing records. Patients were classified as nonadherent if their medication possession ratio, or MPR, was less than 0.8.
Antihypertensive agents were prescribed for 1,929 of the subjects, statins for 1,072, and oral diabetes drugs for 449.
During days 366-730 post breast cancer diagnosis, 37% of the women were nonadherent to antihypertensive medications, 39% to prescribed statins, and 75% to their oral diabetes medications.
Common forms of breast cancer therapy were independently associated with increased likelihood of nonadherence in multivariate logistic regression analysis. For example, chemotherapy was associated with a 67% increased likelihood of nonadherence to diabetes medications during year 2 after breast cancer diagnosis. Patients who received radiation therapy or hormonal therapy were, respectively, 21% and 25% more likely to be nonadherent to antihypertensive therapy.
One factor associated with increased likelihood of adherence to medications for comorbid conditions was greater contact with a primary care physician. Breast cancer survivors who saw their primary care physicians two or more times during year 2 post diagnosis were 70% less likely to be nonadherent to antihypertensive therapy than were those who visited their primary care physicians less frequently.
Greater body mass index was associated with significantly less likelihood of nonadherence to antihypertensive agents but not statins or diabetes medications. When researchers used a BMI below 25 kg/m2 for reference, patients with a BMI of 25-29.9 were 39% less likely to be nonadherent to antihypertensive therapy, those with a BMI of 30-34.9 kg/m2 were 46% less likely, and women with a BMI of 35 kg/m2 or greater were 63% less likely to be nonadherent to their antihypertensive therapy.
A higher Charlson comorbidity score of 2 or more during the first year following breast cancer diagnosis was associated with a 51% reduction in likelihood of nonadherence to diabetes medications during year 2 and a 46% lower nonadherence rate for statins than in patients with a Charlson score below 2.
As reported in previous studies of non-cancer patients, younger age was associated with increased nonadherence. This was true across the board for all three medication classes, although the age effect was most dramatic with respect to nonadherence to statins and oral diabetes medications. Fifty- to 54-year-olds were 3.4- and 1.8-fold more likely than were women age 65 or older to be nonadherent to diabetes drugs and statins, respectively, while breast cancer survivors under age 50 were 7.1- and 2.8-fold more likely to be nonadherent to those types of medications.
Dr. Dawn L. Hershman
Discussant Dawn L. Hershman called the COMBO study medication nonadherence rates “pretty awful.” And if breast cancer survivors aren’t taking their medications for chronic comorbid conditions, it’s not much of a leap to think they may not be adherent to their breast cancer–related medications, she said. She urged her fellow breast cancer specialists to think beyond their specialty focus, consider the patient as a whole, and do what they can to promote adherence to medications targeting these potentially serious comorbidities.
“So, what can we do? We can try to engage technology,” said Dr. Hershman, a medical oncologist at Columbia University, New York.