PROJECT SUMMARY Uterine fibroids are smooth muscle tumors that occur in >80% of Black women and 70% of white women by age 50 years. Fibroids cause heavy menstrual bleeding, pelvic pain or pressure, urinary and bowel dysfunction, infertility, and adverse pregnancy outcomes. Major surgery with hysterectomy and myomectomy is the most common fibroid treatment, but surgery generally requires 2-6 weeks of recovery with substantial time off work and the inability to perform usual activities. To avoid surgery, many women prefer medical therapy for fibroids, but few options are available. There are only two FDA approved oral medications to treat fibroids, GnRH antagonists that block gonadotropins and diminish ovarian estrogen production akin to menopause. These medications require concomitant use of estrogen and progestin “add-back” therapy to mitigate hot flashes and other side effects and risks of low serum estrogen. Many women aim to avoid this long-term hormone therapy or have contraindications to hormone use. New medications that alleviate fibroid symptoms but avoid low serum estrogen are needed to improve care for women with fibroids. Fibroids are hormonally responsive tumors that decrease in volume when deprived of estrogen. The ovary is the primary source of estrogen in premenopausal women, but fibroid cells also produce local estrogen through activity of the aromatase enzyme. Through both autocrine and paracrine action, estrogen produced by fibroids demonstrates local control over fibroid growth. Letrozole is an aromatase inhibitor (AI) that blocks estrogen synthesis within fibroid cells. Therefore, letrozole may decrease fibroid volume and improve symptoms. Low doses of letrozole will inhibit the modest aromatase activity within fibroids, but not significantly block the robust aromatase activity in the ovaries of premenopausal women. Letrozole may serve as a novel therapy that improves fibroid symptoms without adverse effects of low serum estrogen. Despite a biologic mechanism to support AIs as a fibroid treatment, clinical data is very limited. In a few small uncontrolled studies, fibroid volume decreased 35-55% during 8-12 weeks of treatment. We recently completed a pilot, randomized, placebo-controlled trial of letrozole. The letrozole group had greater improvement in fibroid symptoms and quality of life compared with the placebo during 2 months of treatment and reported few side effects. Building on this preliminary data, we propose a full scale randomized, blinded, placebo-controlled trial that is powered to detect clinically meaningful changes in fibroid symptoms and fibroid volume. We will enroll 140 racially and ethnically diverse premenopausal women randomly assigned to oral letrozole 2.5mg/day or an identical placebo for 3 months and assess clinical outcomes and the development of adverse events. We will also evaluate long-term letrozole use with an open-label follow-up phase for up to 6 months of letrozole therapy. This trial will provide gold standard evidence to evaluate the efficacy of a novel treatment for uterine fibroids that has significant advantages over existing medication.

PROJECT NARRATIVE Uterine fibroids are the most common reason women undergo major surgery, with 30,000 myomectomies and 200,000 hysterectomies attributed to fibroids each year. The annual cost of care for women with fibroids is up to $34 billion with the largest burden of this expense (up to $17 billion) due to lost work and disability following fibroid surgery. In this clinical trial, we will evaluate the safety and efficacy of a new oral medication for fibroids that can decrease the large economic and social burden of fibroid surgeries and allow women to select a treatment option that avoids procedural risks and prolonged recovery time.