Adherence to Long-term Adjuvant Hormonal Therapy for Breast Cancer

Carolyn Gotay; Julia Dunn

Disclosures

Expert Rev Pharmacoeconomics Outcomes Res. 2011;11(6):709-715. 

In This Article

Importance of Tamoxifen & Aromatase Inhibitors in Breast Cancer Management

According to the Canadian Cancer Society, an estimated 23,400 Canadian women will be diagnosed with breast cancer in 2011, and 5100 will die from the disease.[1] Breast cancer deaths rates have declined in the past few decades owing to several factors, including better approaches to early detection and advances in cancer treatment. Particularly significant among these advances is the use of tamoxifen to prevent recurrence and second primary breast cancers.

Tamoxifen, a selective estrogen receptor modulator (SERM), has been used to treat breast cancer for more than 30 years,[2] with the WHO citing tamoxifen as an essential drug in breast cancer treatment.[3] It is estimated that more than 400,000 women are alive today because of tamoxifen therapy, and millions more have benefited from palliation and extended disease-free survival.[3] Tamoxifen is administered adjuvant to primary treatment of early stage hormone-sensitive breast cancer, helping to prevent the original breast cancer from returning.[4] Tamoxifen is also effective in preventing the development of new breast cancer tumors and has been used to treat ductal carcinoma in situ, a noninvasive condition that may lead to the development of invasive breast cancer.[5] In the context of primary prevention, the use of tamoxifen is associated with an overall 49% reduction in invasive cancer.[6,7] In addition, patients taking tamoxifen experience reductions in the frequency of deaths from myocardial infarction as well as significant protection against bone loss.[8]

Aromatase inhibitors (AIs), which work through blocking the synthesis of estrogen, have also been found to be effective in the prevention of primary breast cancers and their recurrence. Specific agents used most widely in breast cancer to date include anastrozole, exemestane and letrozole. AIs have demonstrated significant benefits, comparable to or better than those seen with tamoxifen, which has led to their use being recommended by multiple international consensus panels.[9,10] Like tamoxifen, AIs require long-term daily self-administration of an oral medication.

To be effective in achieving the reduction in recurrence rates that are possible, the prescribed regimen must be adhered to. Studies have indicated that women who adhere to tamoxifen less than fully (i.e., <80%) are more likely to die than women who are more adherent.[11,12] Other consequences are possible as well. If a primary care physician is not aware that a patient is not taking the therapy prescribed, he or she may attribute progression of disease to a lack of efficacy and unnecessarily change the treatment.[13] Additionally, nonadherence has been found to increase the consumption of healthcare resources in some patient populations.[13] However, despite the patient benefits associated with adjuvant hormonal therapies and, conversely, the negative outcomes associated with their absence, adherence to endocrine therapies remains far less than optimal.

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