P–299 Efficacy and safety of linzagolix for the treatment of severe adenomyosis: Initial results from a pilot study

Study question Is a once daily regimen of the GnRH antagonist, linzagolix, high-dose (200mg) for 12 weeks then low-dose (100mg) for 12 weeks, effective in severe adenomyosis? Summary answer After 12 weeks, there was marked shrinkage of uterine volume, regression of adenomyotic lesions and symptom improvement (pain, anemia), 24 weeks data is pending. What is known already Suppression of estradiol using GnRH antagonists has been shown to be an effective treatment for endometriosis and uterine fibroids. Linzagolix is an investigational, oral GnRH receptor antagonist, which dose-dependently reduces E2 levels, providing full suppression (serum E2 < 20 pg/mL) and partial suppression with once daily oral dosing of 200 mg and 100 mg, respectively. We hypothesized that a regimen of full suppression for 12 weeks followed by partial suppression maintenance therapy for 12 weeks could be effective for the treatment of severe adenomyosis. Study design, size, duration This was a single-center, open-label exploratory study in women with symptomatic adenomyosis confirmed by Magnetic Resonance Imaging (MRI) (EudraCT number: 2017–004–042–14). Patients were recruited from a single private clinic and infertility research unit between March 2019 to June 2020. Participants/materials, setting, methods Eligible patients were premenopausal women 18 to 48 years old with symptomatic uterine adenomyosis confirmed by MRI, moderate-to-severe pain and abnormal uterine bleeding. The primary measure of efficacy was the reduction in uterine volume assessed by MRI. Other endpoints included adenomyosis lesion volume, pelvic pain, haemoglobin, uterine bleeding and quality of life (EHP–30 domains: pain, control and powerlessness, emotional well-being, social support and self-image). Main results and the role of chance Eight (3 black and 5 white) enrolled subjects had mean±SD age 42±3 years and weight 75±19 kg. At baseline (day 2 of the cycle) all patients presented with pelvic pain, severe dysmenorrhea and heavy menstrual bleeding. In all cases, MRI showed an enlarged uterus (mean±SD volume 343±253 cm3) with severe adenomyosis characterized by heterogenous myometrium with multiple myometrial cysts. The mean±SD junctional zone was 29.0±14.2 mm. Median serum estradiol was suppressed to 12 pg/mL by 4 weeks and this was maintained up to 12 weeks. After 12 weeks, mean±SD uterine volume was 162±117 cm3, a 57±16% reduction from baseline, with marked regression of adenomyotic lesions and the junctional zone was 21.0±13.4 mm. Mean±SD overall pelvic pain score (0–10 NRS) was reduced from 8.4±1.1 at baseline to 2.4±3.4 (p = 0.0035) and there were also improvements in dysmenorrhea, dyspareunia, non-menstrual pelvic pain and dyschezia scores. No subjects reported uterine bleeding between Weeks 4 to 12. Mean±SD haemoglobin was 12.1±2.0 at baseline and 12.8±1.1 at 12 weeks. Anemia at baseline (≤10g/dL) was resolved by 12 weeks. Substantial improvements were observed on each of the EHP–30 domains. The most common side effect was the expected hypoestrogenic side effects of hot flushes, which were reported by 6/8 subjects. Limitations, reasons for caution This was a single-centre, open-label pilot study in 8 patients with symptomatic adenomyosis. We report the results after the first 12 weeks treatment of a high full suppression dose of linzagolix. Results after 24 weeks will further inform on the potential for a low partial suppression dose to maintain efficacy. Wider implications of the findings: The initial results of this open-label pilot study in women with severe adenomyosis indicate that a high full suppression dose of linzagolix 200 mg is effective in reducing uterine and adenomyosis lesion size, reducing abnormal uterine bleeding and pelvic pain and improving quality of life. Trial registration number EudraCT number: 2017–004–042–14