Proliferative Mucinous Lesions of the Endometrium: Analysis of Existing Criteria for Diagnosing Carcinoma in Biopsies and Curettings

It is often difficult to make a diagnosis of carcinoma in endometrial biopsies and curettings that show proliferative mucinous lesions because of the deceptively bland appearance of invasive mucinous adenocarcinoma at this site. Only limited information is available regarding criteria for distinguishing mucinous carcinoma from atypical mucinous proliferations and mucinous metaplasia of the endometrium. The threshold for diagnosing mucinous carcinoma in endometrial biopsies/curettings may possibly be lower than that for endometrioid carcinoma. We evaluated different sets of existing criteria in order to determine which best facilitate a diagnosis of carcinoma in endometrial biopsies/curettings containing mucinous lesions. The biopsy/curetting samples with the corresponding uterus (hysterectomy performed within 6.5 months) from each of 31 patients were studied. The biopsies/curettings were assessed with previously published criteria that more typically are used for endometrioid proliferations, as well as recently proposed criteria for mucinous lesions (Mod Pathol 12:1137-1142, 1999; Nucci et al. criteria [Type A, B, or C]). The presence of myoinvasion in the uterus was used as the gold standard for testing the biopsies/curettings. The sensitivity and specificity of diagnosing carcinoma with use of endometrioid criteria were 20.0% and 71.4%, respectively, while the corresponding figures for diagnosing carcinoma with use of the criteria of Nucci et al. were 0% and 81.0% (Type A), 70.0% and 52.4% (Type B), and 30.0% and 66.7% (Type C), respectively. Combining the Types B and C criteria of Nucci et al. into a single category (Combined Type B or C) yielded a sensitivity and specificity of 100% and 19.0%, respectively, for diagnosing carcinoma. With use of a diagnosis of carcinoma by endometrioid criteria and application of the criteria of Nucci et al. for mucinous lesions, myoinvasive carcinoma was present in the uterus in 25.0% (endometrioid criteria) and 0%, 41.2%, 30.0%, and 37.0% (Types A, B, C, and Combined Type B or C, respectively) of cases, respectively. Because of the high sensitivity/low specificity of the criteria of Nucci et al. and low sensitivity/high specificity of endometrioid criteria in this small study, neither of the sets tested is perfect for handling mucinous proliferations. However, the criteria of Nucci et al. do have utility. Application of the criteria available for endometrioid proliferations in biopsies/curettings that show mucinous lesions may be misleading.