Improving Adherence to Endocrine Therapy in Women With HR-Positive Breast Cancer

May 15, 2018
Julia P. Brockway, MD

,
Charles L. Shapiro, MD

Here, we discuss how to improve adherence to endocrine therapy in women with HR-positive breast cancer, as well as the side effects and the reasons for discontinuation.

Aromatase inhibitors (AIs) are the standard treatment for postmenopausal women with hormone receptor–positive breast cancers. One of the most common side effects of AIs is joint pain; it is also the most frequently cited reason for nonadherence and discontinuation before completion of the prescribed treatment course. Nonadherence and, in particular, discontinuation, can lead to increased rates of breast cancer mortality. The prevalence of AI-induced arthralgias is about 50%, and there are several interventions, including switching to a different AI, that can increase adherence. The healthcare professional plays a part in fostering adherence by communicating the side effects of AIs to patients before the initiation of treatment, as well as explaining the strategies for addressing these side effects, should they occur.

Introduction

Adjuvant endocrine therapy is the standard of care for women with estrogen receptor– and progesterone receptor–positive breast cancers. Endocrine therapies include aromatase inhibitors (AIs), such as the nonsteroidal compounds letrozole and anastrozole and the steroidal compound exemestane. All three AIs have comparable benefits and side effect profiles. The selective estrogen receptor modulator tamoxifen has anticancer activity in pre- and postmenopausal women. While AIs only have anticancer activity in postmenopausal women, they are superior to tamoxifen at reducing the risk of recurrence and improving overall survival.[1-3]

AIs and tamoxifen require long-term daily self-
administration of oral medications for 5 years, and in some cases, 10 years. However, up to 28% of women in clinical trials, and as many as 73% in community practice settings, prematurely discontinue these drugs.[4-6] AI adherence in particular is suboptimal, ranging from 50% to 91% over 5 years of therapy,[6] and only 40% to 60% of women complete the recommended course of AIs.[7-9] A consequence of nonadherence and discontinuation is an increase in breast cancer mortality.[8-10]

Medication “adherence” is synonymous with medication “compliance.” Adherence is measured over time and reported as a percentage.[11] The preference for “adherence” over “compliance” is due to the former term’s less harsh and judgmental connotations regarding patients’ behavior.[12] Persistence is the duration of time from initiation to discontinuation of therapy, and is a continuous variable referring to the duration of treatment.[11,12] Persistence is a specific aspect of adherence.

There are several ways to measure adherence. One method is to review prescription refill data and the medication possession ratio (MPR). The MPR is the ratio of total days of medication divided by the entire duration of days that the drug is prescribed for, with adherence defined as > 80%.[8] Another method of measuring adherence is to use patient-reported data, which may take into account behaviors and experiences. The most straightforward and reliable way to measure adherence is to ask the patient if she is taking the medication.

Risk Factors Leading to Treatment Nonadherence and Discontinuation

There are many independent risk factors for treatment nonadherence and discontinuation, including adverse effects; disease stage; use of chemotherapy (ie, taxanes); comorbidities; demographic features such as age, lower socioeconomic status, and race; and psychosocial factors such as quality of life, emotional distress, attitude toward therapy, and perception of self-efficacy.[13-16]

Adverse effects are the most common reason for nonadherence to and discontinuation of endocrine therapy. A survey of 538 women with early-stage breast cancer receiving endocrine treatments found that 18% of women discontinued therapy within 5 years, and 94% of them experienced adverse effects. Among those who discontinued AIs, two-thirds reported that they “did not like the adverse effects.”[15] Importantly, about 25% of the women in this study discontinued treatment without consulting a medical provider, thus missing an opportunity for guidance or shared decision making.

Adverse Effects of Endocrine Therapy

The adverse effects of endocrine therapy include hot flashes, vaginal dryness, dyspareunia, osteoporosis, and arthralgia/myalgia. For many of these side effects, there are proven interventions, including venlafaxine or gabapentin for hot flashes; vaginal moisturizers, dehydroepiandrosterone, the intravaginal laser MonaLisa Touch, and minimal doses of intravaginal estrogens for dyspareunia or vaginal dryness; and vitamin D and calcium supplementation, bisphosphonates, and denosumab for osteoporosis and osteopenia. Here, we will focus on arthralgia and myalgia, because mitigating these symptoms can prove especially challenging.

Arthralgia and myalgia are the most common side effects of AI treatment and contribute the most to nonadherence and discontinuation. The prevalence of AI-induced arthralgia is 50% (range, 20% to 73%).[17] Some studies combine data on arthralgia and myalgia, referring to the two together as ‘musculoskeletal symptoms.’[18] We have followed this practice here, using the term ‘AI-induced arthralgia’ to encompass myalgia as well. In one study of women with early-stage breast cancer receiving an adjuvant AI, more than half of those who discontinued treatment reported grade 2/3 arthralgia as the reason.[19]

The primary criteria defining AI-induced arthralgia are:

• Joint pain develops or worsens while a patient is taking an AI.

• If the AI is stopped for 3 weeks, the joint pain goes away. When the AI is subsequently restarted, the joint pain returns.[20]

Minor criteria include:

• The joints are affected symmetrically.

• The patient complains of pain in the hands or wrists, carpal tunnel syndrome, and/or decreased grip strength.

• Joint stiffness is worse in the morning.

• Exercise improves symptoms.

AI-induced arthralgia tends to occur soon after initiating treatment with an AI, with a median onset of 1.6 months (range, 0.4 to 10 months).[20] The mechanism(s) of AI-induced arthralgia are not entirely understood.[21] MRI findings show tenosynovitis with enhancement and thickening of the tendon sheaths, consistent with an inflammatory process.[22]

Our Approach to Maximizing Treatment Adherence to AI Therapy

In clinical practice, the biggest challenge of treating hormone receptor (HR)-positive breast cancer patients is helping them maintain adherence and complete the prescribed course of AI treatment. Some of the questions that clinicians often struggle with include: How do you know that the patient receiving an AI is experiencing AI-induced arthralgia, and what distinguishes it from osteoarthritis? What are the proven interventions for AI-induced arthralgia? Finally, what is the role of the healthcare provider in increasing adherence and decreasing discontinuation rates? Our experience mirrors the literature.[23]

Before starting AI therapy, weight management and increasing physical activity should be part of the routine care of every woman with breast cancer. Obesity increases breast cancer mortality, and increasing physical activity (ie, from being sedentary), though not proven, may decrease breast cancer mortality. Increasing physical activity has a wealth of benefits beyond breast cancer, and may mitigate AI-induced arthralgia. It is beyond the scope of this article to discuss the ‘teachable moment’[24] and the ways to effect behavior modification. However, three points are worth mentioning. The first point is that women receiving AIs desire information from their oncology provider about AI-induced arthralgia, and are more likely to increase physical activity if their oncologists recommend it.[25] Second, if AI-induced arthralgia occurs, despite maintaining optimal physical activity, there are approaches to mitigate it. Finally, it should be noted that there is a placebo effect in all intervention trials. For example, as many as 50% of women reported improvements in joint pain while receiving a placebo in a randomized placebo-controlled trial of omega-3 fatty acids for AI-induced arthralgias.[26] From the patient’s point of view, it doesn’t matter whether it’s a therapeutic effect of an intervention or the placebo effect, as long as it relieves the joint pain.

Typically, we start endocrine treatment with the nonsteroidal compound anastrozole. If the patient has any preexisting arthritis, we note the sites of joint pain. As discussed previously, we describe the relatively rapid onset of AI-associated joint pain, and its typical pattern of affecting the joints symmetrically. To assess adherence, we directly ask the patient if she is taking her medication.[27]

If new joint symptoms appear while a patient is taking an AI, do not respond to over-the-counter medications, and are of sufficient magnitude to affect activities of daily living, we recommend stopping the AI for 2 to 4 weeks. If the joint pain persists, it is not likely related to the AI. If the joint pain improves, we recommend a rechallenge with the same AI. If the joint pain reoccurs, then a causal relationship between the particular AI and the joint pain is established.

One of the simplest and most effective interventions is switching from one AI to another or to tamoxifen[28,29]; about one-third of women who switch to another AI can tolerate the second AI for a median of nearly 14 months (range, 3 to 39 months).[30] For example, we would switch to the steroidal compound exemestane if anastrozole causes intolerable side effects. If exemestane results in joint pain, and rechallenge provokes the same joint pain, we would typically try tamoxifen in women for whom there are no absolute contraindications to this drug.

There are several recent systematic reviews of other interventions, including high-dose vitamin D3­, omega-3 fatty acids, duloxetine, acupuncture, aerobic and resistance exercise training, yoga, and tai chi.[18,31] Many of the intervention trials have methodological problems, including small sample sizes, the inclusion of only retrospective or prospective cohorts, the use of different entry criteria for baseline level of joint pain, and the use of different instruments to measure the primary endpoint of joint pain, as well as secondary endpoints.

The results of acupuncture trials and exercise interventions, as well as studies on vitamin D3, are mixed.[18] Higher doses of omega-3 fatty acids in randomized controlled trials were shown to be ineffective at reducing AI-induced arthralgia.[18] Recently, the results of a randomized placebo-controlled trial of duloxetine showed statistically and clinically significant reductions in joint pain in women receiving AIs.[32] At Mount Sinai, there is an ongoing randomized controlled trial of hypnosis for women with AI-induced arthralgia. We encourage eligible patients to enroll in this trial. The uptake of the trial is high because it uses a nondrug intervention. We also often refer women with AI-induced arthralgia for acupuncture, despite the mixed trial results.

As healthcare providers, we tend to underestimate the role we play in maintaining adherence and reducing discontinuation. It is important to remember that adherence depends to a considerable degree on good physician/patient communication, as well as on the strength of the therapeutic relationship; good communication should include clear and careful explanations of risks, benefits, and alternatives to treatment.

Financial Disclosure: The authors have no significant financial interest in or other relationship with the manufacturer of any product or provider of any service mentioned in this article.

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