Assessment of progestin‐only therapy for endometriosis in macaque

Abstract Background Endometriosis is a condition where endometrium‐like tissue forms lesions at ectopic sites outside the uterus. In women, oral contraceptive pills and progestins are often prescribed as therapy for early stage endometriosis. In contrast, in macaques the disease is frequently advanced at the time of diagnosis and ovariectomy is the standard therapy. However, surgery is contraindicated in many patients. A review of 15 endometriosis cases over the past 10 years at the Oregon National Primate Research Center (ONPRC) revealed that 5 failed to show improvement after ovariectomy and were subsequently euthanized. Therefore, our goal was to assess the feasibility of treating endometriosis in macaques with chronic progesterone (P) as an alternative therapy for the disease. Methods Seven adult rhesus macaques with advanced endometriosis were identified by clinical symptoms and endometriosis was confirmed by abdominal palpation, ultrasound examination, and/or aspiration of menstrual blood from abdominal cysts. The patients were chronically treated with Silastic capsules that released 5–7 ng P /ml in blood for up to 20 months. During treatment the patients were assessed daily and scored numerically for appetite, activity, attitude, abdominal discomfort and menstruation by the Clinical Veterinary staff. The patients were then re‐examined by abdominal palpation and ultrasound for the disease at the end of treatment. Results During the first 2 weeks of treatment, endometriotic symptoms improved significantly in all the patients ( P < 0.05). This was associated with a significant increase in body weight and significant reduction in abdominal discomfort and menstrual bleeding. Two of the patients gradually developed increased symptoms of the disease after 5 months of treatment. Post‐treatment abdominal examination revealed that 2/5 patients continued to have an abdominal mass even though symptoms were suppressed. Conclusions We conclude that continuous P treatment of rhesus monkeys provides therapeutic benefit to reduce symptoms of endometriosis and may provide an option for cases where ovariectomy is contraindicated. Supported by RR‐00163.