Abstract 1049: Prevalence of KDM6A expression loss in human cancer: A tissue microarray study on 6,560 cancers from 114 different tumor types

Abstract KDM6A, also known as UTX (ubiquitously transcribed X chromosome tetratricopeptide repeat protein) is an epigenetic regulator constituting a critical part of the COMPASS-like complex. KDM6A mutations occur commonly in cancer. These are of interest because KDM6A loss results in a dependency on EZH2, a potential therapeutic target. Most data on KDM6A have been obtained by next generation sequencing (NGS). However, since most KDM6A mutations are truncating and KDM6A is located on the X chromosome, many mutations result in a complete expression loss which can be detected by immunohistochemistry (IHC). To learn more on the prevalence of KDM6A expression loss and its role in cancer, a tissue microarray containing 6,560 samples from 114 different tumor entities and 608 samples of 76 different normal tissue types was analyzed. In normal tissues, KDM6A staining was rather ubiquitously seen in nuclei. In cancer, KDM6A staining was considered weak (1+) in 581 (11.2%), moderate in 1,927 (37%), and strong in 2,362 (45.4%) of 5,206 interpretable tumors. A complete loss of KDM6A staining occurred in 336 (6.5%) of tumors. At least one case with a complete KDM6A expression loss was observed in 51 of 114 tumor categories. KDM6A staining was most commonly lost in different categories of urothelial carcinomas (19.5-39.2%), squamous cell carcinomas of the esophagus (27.1%), hepatocellular carcinoma (18.4%), gastric carcinoma (3.2-12.5%), papillary renal cell carcinoma (9.5%), adenocarcinoma of the prostate (5.9-9.4%), chromophobe renal cell carcinoma (8.9%), Ewing sarcoma (8.3%), pheochromocytoma (8.3%), and metastatic malignant melanoma (8%). A KDM6A expression loss in less than 8% of cases was observed in 32 further tumor entities. KDM6A expression loss was more than twice as frequent in tumors from male (8.4% of 2,526) than in tumors from female patients (3.9% of 2,024; p<0.0001). It is concluded that KDM6A IHC is a suitable method for the detection of truncating KDM6A mutations, especially in males. These make up for about 2/3 of all KDM6A mutations and may exert specific biological effects than differ from the various KDM6A missense mutations known to also occur. Citation Format: Florian Viehweger, Natalia Gorbokon, Maximilian Lennartz, Viktor Reiswich, Florian Lutz, Till Krech, Andreas M. Luebke, Claudia Hube-Magg, Guido Sauter, Ronald Simon, Stefan Steurer, Andreas H. Marx, Christian Bernreuther, Martina Kluth, Sarah Minner. Prevalence of KDM6A expression loss in human cancer: A tissue microarray study on 6,560 cancers from 114 different tumor types [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1049.