Is the two-tier ovarian serous carcinoma grading system potentially useful in stratifying uterine serous carcinoma? A large multi-institutional analysis

Abstract Objective A subset of uterine serous carcinoma (USC) may have better clinical behavior bringing up the possibility that there may be morphologic features, which would help in their categorization. The aim of this study is to evaluate the potential use of the MD Anderson Cancer Center 2-tier grading system for ovarian carcinoma in USC. Methods Tumors assigned a combined score included in this analysis were 1) low-grade: tumors without marked atypia and 12 mitoses/10 high power field (HPF) and 2) high grade: tumors with severe nuclear atypia and >12 mitoses/10 HPF. Clinicopathologic parameters evaluated included patients' age, tumor size, myometrial invasion (MI), lymphovascular invasion (LVI), lymph node (LN), FIGO stage, and patient outcome. Results 140 patients with USC were included, 30 low grade uterine serous carcinoma (LGUSC) and 110 high grade uterine serous carcinoma (HGUSC). Of all parameters only 2 (MI and stage IA) reached statistical significance. 67% of LGUSC cases showed myometrial invasion versus 93.6% HGUSC cases (p=0.003). A higher percentage of LGUSC (63.3%) versus HGUSC (32.7%) were in stage IA (p=0.01). However, by multivariate analysis including age, LVI, stage and tumor grade only stage was an independent prognostic factor. Conclusion The presence of atypia and mitosis across a uterine serous carcinoma is notoriously variable in magnitude and extent, potentially making evaluation of these features difficult and subsequent grading subjective. Our findings thus show that actual prognostic utility of application of MDACC two-tier grading system to uterine serous carcinoma may not be applicable.