Postmenopausal women with hormone receptor-positive (HR+) breast cancer who develop arthralgia and/or myalgia (A/M) while being treated with anastrozole may want to consider a switch to letrozole therapy, researchers said at the 32nd Annual San Antonio Breast Cancer Symposium (SABCS).

In fact, their study – known as the Rheumatologic Evaluation of Adjuvant Letrozole in Postmenopausal Women with Breast Cancer (REAL) study – found that women who experienced ≥ grade 2 A/M while receiving anastrozole and switched to letrozole developed significantly less A/M and had an improved quality of life compared with baseline.

Denise A. Yardley, MD, Director of Breast Cancer Research at the Sarah Cannon Research Institute in Nashville, Tennessee, and colleagues conducted a study to determine whether switching to letrozole reduced the rate of grade 2 to 3 A/M symptoms and the rate of discontinuation in 261 women who had previously discontinued anastrozole therapy due to A/M.

Non-steroidal aromatase inhibitors are the standard of care in the adjuvant treatment of postmenopausal women with HR+ early breast cancer, Dr. Yardley observed. However, side effects such as A/M may occur in up to a third of women on aromatase inhibitor therapy with onset as early as one to two months from the start of aromatase inhibitor therapy. As many as 20% of patients may stop therapy as a result, she added.

Switching to another aromatase inhibitor could improve A/M and allow patients to remain on aromatase inhibitor therapy, she said.

Women were eligible for letrozole treatment (2.5 mg/d for six months) if they were postmenopausal, HR+, had early stage breast cancer, and experienced grade 2-3 A/M on anastrozole resulting in therapy discontinuation.

Patients tolerating letrozole therapy at six months had the option of continuing letrozole for their prescribed course of five years.

The primary endpoint was the percentage of women discontinuing letrozole due to ≥ grade 2 A/M.

At baseline, 107 (41.0%) women and 70 (26.8%) women had grade 2 or higher A/M, respectively, versus 61 (23.6%) and 46 (17.8%), at six months.

Overall, 228 women, or 87.4%, remained on letrozole therapy until the end of the six-month study.

Only 25 (9.6%) of 261 women discontinued due to A/M and another 8 (3.1%) discontinued for other reasons.

Significant improvements in all quality of life endpoints were reported at six, 12, and 24 weeks. Thus, after the switch, patients had improvements in their Brief Pain Inventory (BPI) composite score, Health Assessment Questionnaire in short form (HAQ), and HAQ visual analog Scale (VAS).

Neither age, baseline A/M grade, baseline vitamin D level, body mass index, or history of pain medications predicted time to discontinuation of letrozole.

“The strategy of switching to letrozole after discontinuation of anastrozole due to grade 2 to 3 A/M enables patients to continue with aromatase inhibitor therapy and thus maximize their adjuvant aromatase therapy benefit,” Dr. Yardley observed.

Written by Jill Stein
Jill Stein is a Paris-based freelance medical writer.