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Primary endometrial carcinomas with somatically derived yolk sac tumor (YST) components are rare. We analyzed 23 such cases using detailed clinicopathologic, immunohistochemical, and molecular methods. The median patient age was 68 years. Elevated serum alpha-fetoprotein (AFP) was detected in 76.9% (10/13) of tested cases. FIGO (2009) stages were I (n = 12, 55%), II (n = 1, 5%), III (n = 5, 23%), IV (n = 4, 18%), and unknown in one. Histologic YST patterns included glandular (87%), papillary (52%), solid (48%), endodermal sinus (17%), hepatoid (17%), and reticular (13%) architectures. The associated Müllerian-type neoplasms were endometrioid carcinoma (n=17), carcinosarcoma (n=3), serous carcinoma (n=2), and clear cell carcinoma (n=1). Immunohistochemically, 17 cases (74%) exhibited mutation-type p53 staining, and two (9%) were mismatch repair-deficient (MMRd). YST components uniformly expressed glypican-3 and spalt-like transcription factor, while 17 (74%) also expressed AFP. HER2 positivity was seen in 13 of 21 tested (62%; four 3+, three 2+, six 1+). Molecular analysis revealed TP53 variants in 16 of 22 cases (73%) without POLE hotspot mutations. According to The Cancer Genome Atlas molecular classification, 17 tumors were p53-abnormal (74%), two (9%) MMRd, four (17%) were no specific molecular profile (NSMP), and none were POLE-ultramutated. Recurrent copy number gains involved CCNE1 (9/22, 41%), 1q44 (12/14, 86%), and 3q26.32 (8/14, 57%). Features reminiscent of germ cell tumours included amplifications at 7p21.2 (8/14, 57%) and 9p21.3 (11/14, 79%), polysomy or amplification of chromosome 12p (6/22, 27%), deletion at 11q24.3 (8/14, 57%), and a high frequency of T>C nucleotide substitutions. Follow-up showed 15 patients (75%) had died of disease or were alive with disease; 12 of these 15 cases were p53-abnormal. Overall survival was significantly poorer than in other molecular subtypes of endometrial carcinoma. These tumors should therefore be regarded high-grade (grade 3) by definition. In summary, endometrial carcinomas with a somatically derived yolk sac tumor component are highly aggressive, predominantly p53-abnormal, with smaller subsets classified as MMRd or NSMP. Recognition of the YST component is crucial, and biomarker profiling may reveal therapeutic targets.