Uterine effects of estrogen plus progestin therapy and raloxifene: adjudicated results from the EURALOX study.

Objective: To compare the incident rate of abnormal endometrial findings in postmenopausal women receiving treatment with either 60 mg of raloxifene or a continuous combined estrogen plus progestin therapy containing 2 mg of 17 beta-estradiol plus 1 mg of norethisterone acetate for a duration of up to 12 months.

Methods: One thousand eight asymptomatic postmenopausal women with osteoporosis or cardiovascular risk factors with an endometrial thickness of less than 5 mm at baseline participated in this prospective, randomized, double-blind trial that lasted 6 months; 347 of these women also participated in a 6-month extension. Women with repeated bleeding or an increase in endometrial thickness to above 5 mm were subjected to saline-infused sonohysterography or hysteroscopy with biopsy. Sonographic, histologic, and clinical findings were adjudicated by a panel of 4 experts blinded with respect to patients' treatments. All adjudicated patients were grouped into 15 diagnostic categories according to predefined criteria.

Results: Three hundred thirty-four women needed adjudication during the core phase, 73 (14.7%) of those taking raloxifene and 261 (50.9%) taking continuous combined estrogen plus progestin therapy (P <.001). Compared with raloxifene, women using continuous combined estrogen plus progestin therapy had significantly higher rates of benign endometrial proliferation (8.8 versus 1.2%, P <.001), endometrial polyps (4.3 versus 2.0%, P =.048), and cystic atrophy (5.5 versus 1.2%, P <.001).

Conclusion: Women using continuous combined estrogen plus progestin therapy more often have benign endometrial pathology and, in our study, more often required the protocol-specific gynecological follow-up assessments for safety reasons, as compared with those using raloxifene. These findings are of clinical relevance when choosing the most appropriate therapy for postmenopausal health risks such as osteoporosis.