An Endometrioid Carcinoma With an Adenoma Malignum-like Pattern of Invasion: New Insight into Molecular Features

Adenoma malignum-like (AM-L) pattern is the least common invasion type in endometrioid carcinoma of the uterus and is characterized by a bland morphologic appearance in accordance with International Federation of Gynecology and Obstetrics Grade 1 endometrioid carcinoma. However, the biological behavior of the AM-L pattern is not always indolent, and it may present at an advanced tumor stage. Although several studies have described the clinicopathological features of this pattern, the molecular alterations have not yet been explored. Here, we report a case of endometrioid carcinoma with AM-L invasion pattern and analyzed its genetic alterations using a next-generation sequencing panel that included 571 genes. Six single nucleotide variations or insertion/deletion alterations were detected, including ARID1A exon 4 c.1848dup p.(S617Lfs*6), CTNNB1 exon 3 c.101G>A p.(G34E), PTEN exon 5 c.332G>A p.(W111*), PTEN exon 6 c.548dup p.(N184Efs*6), BCOR exon 10 c.4376A>G p.(N1459S), and MAPK4 exon 6 c.1594G>A p.(G532S). Neither POLE nor TP53 alteration was detected. No copy number variations or gene fusions were observed. The microsatellite status was stable, and the tumor mutational burden was low. The molecular features demonstrate the endometrioid nature of the AM-L pattern. Further studies are needed to explore the significance of these genetic alterations in this particular pattern and to clarify their oncogenic mechanism.