Clinicopathological characteristics of multiple-classifier endometrial cancers: a cohort study and systematic review

Background: Endometrial cancers with more than one molecular feature-POLE mutations (POLEmut), mismatch repair protein deficiency (MMRd), p53 abnormality (p53abn)-are called 'multiple classifiers'. Objective: To describe our cohort of multiple classifiers and to report the results of a review on their incidence and the techniques used to identify them. Methods: Multiple classifiers identified at the European Institute of Oncology, Milan, between April 2019 and Decmber 2022, were included. Clinicopathological, molecular characteristics, and oncologic outcomes were summarized and compared between single and multiple classifiers sharing common features. Studies on molecular classification of endometrial cancer were searched in the PubMed Database to collect data on the incidence of multiple classifiers and the techniques used for classification. Results: Among 422 patients, 48 (11.4%) were multiple classifiers: 15 (3.6%) POLEmut-p53abn, 2 (0.5%) POLEmut-MMRd, 28 (6.6%) MMRd-p53abn, and 3 (0.7%) POLEmut-MMRd-p53abn. MMRd-p53abn and MMRd differed in histotype (non-endometrioid: 14.8% vs 2.0%, p=0.006), grade (high-grade: 55.6% vs 22.2%, p=0.001), and MMR proteins expression, whereas they differed from p53abn in histotype (non-endometrioid: 14.8% vs 50.0%, p=0.006). POLEmut-p53abn and POLEmut differed only in grade (high-grade: 66.7% vs 22.7%, p=0.008), while they differed from p53abn in age (56.1 vs 66.7 years, p=0.003), stage (advanced: 6.7% vs 53.4%, p=0.001), and histotype (non-endometrioid: 6.7% vs 50.0%, p=0.002). Two (7.1%) patients with MMRd-p53abn, 4 (4.0%) with MMRd, and 25 (34.3%) with p53abn had a recurrence. No recurrences were observed in POLEmut-p53abn and POLEmut. TP53 sequencing allowed the detection of additional 7 (18.9%) multiple classifiers with normal p53 immunostaining. The incidence of multiple classifiers ranged from 1.8% to 9.8% in 10 published studies including >100 patients. When only p53 immunohistochemistry was performed, the highest incidence was 3.9%. Conclusions: The characteristics of POLEmut-p53abn resembled those of POLEmut, whereas MMRd-p53abn appeared to be intermediate between MMRd and p53abn. The high proportion of multiple classifiers may be related to the methods used for molecular classification, which included both p53 immunohistochemistry and TP53 sequencing.