Loss of S-methyl-5′-thioadenosine phosphorylase (MTAP) expression is a common event in cancer leading to a critical vulnerability of cancer cells towards anti-cancer drugs. Homozygous MTAP deletions result in a complete expression loss that can be detected by immunohistochemistry (IHC). In this study, a tissue microarray containing 17,078 samples from 149 different tumor entities was analyzed by IHC, and complete MTAP loss was validated by fluorescence in situ hybridization. MTAP loss was observed in 83 of 149 tumor categories, including neuroendocrine neoplasms (up to 80%), Hodgkin lymphoma (50.0%), mesothelioma (32.0% to 36.8%), gastro-intestinal adenocarcinoma (4.0% to 40.5%), urothelial neoplasms (10.5% to 36.7%), squamous cell carcinomas (up to 38%), and various types of sarcomas (up to 20%) and non-Hodgkin lymphomas (up to 14%). Homozygous MTAP deletion was found in 90% to 100% of cases with MTAP expression loss in most tumor categories. However, neuroendocrine tumors, Hodgkin lymphomas, and other lymphomas lacked MTAP deletions. MTAP deficiency was significantly linked to unfavorable tumor phenotype in selected tumor entities and the presence of PD-L1 expression on tumor cells, absence of PD-L1 expression on immune cells, and a low density of CD8⁺ lymphocytes. In summary, MTAP deficiency can occur in various tumor entities and is linked to unfavorable tumor phenotype and noninflamed tumor microenvironment, but is not always related to deletions. MTAP IHC is of considerable diagnostic value for the detection of neoplastic transformation in multiple different applications.

EpCAM is expressed in many epithelial tumors and is used for the distinction of malignant mesotheliomas from adenocarcinomas and as a surrogate pan-epithelial marker. A tissue microarray containing 14,832 samples from 120 different tumor categories was analyzed by immunohistochemistry. EpCAM staining was compared with TROP2 and CKpan. EpCAM staining was detectable in 99 tumor categories. Among 78 epithelial tumor types, the EpCAM positivity rate was ≥90% in 60 categories—including adenocarcinomas, neuroendocrine neoplasms, and germ cell tumors. EpCAM staining was the lowest in hepatocellular carcinomas, adrenocortical tumors, renal cell neoplasms, and in poorly differentiated carcinomas. A comparison of EpCAM and CKpan staining identified a high concordance but EpCAM was higher in testicular seminomas and neuroendocrine neoplasms and CKpan in hepatocellular carcinomas, mesotheliomas, and poorly differentiated non-neuroendocrine tumors. A comparison of EpCAM and TROP2 revealed a higher rate of TROP2 positivity in squamous cell carcinomas and lower rates in many gastrointestinal adenocarcinomas, testicular germ cell tumors, neuroendocrine neoplasms, and renal cell tumors. These data confirm EpCAM as a surrogate epithelial marker for adenocarcinomas and its diagnostic utility for the distinction of malignant mesotheliomas. In comparison to CKpan and TROP2 antibodies, EpCAM staining is particularly common in seminomas and in neuroendocrine neoplasms.

Stimulator of interferon genes protein (STING) activates the immune response in inflammatory cells. STING expression in cancer cells is less well characterized, but STING agonists are currently being evaluated as anticancer drugs. A tissue microarray containing 18,001 samples from 139 different tumor types was analyzed for STING by immunohistochemistry. STING-positive tumor cells were found in 130 (93.5%) of 139 tumor entities. The highest STING positivity rates occurred in squamous cell carcinomas (up to 96%); malignant mesothelioma (88.5%–95.7%); adenocarcinoma of the pancreas (94.9%), lung (90.3%), cervix (90.0%), colorectum (75.2%), and gallbladder (68.8%); and serous high-grade ovarian cancer (86.0%). High STING expression was linked to adverse phenotypes in breast cancer, clear cell renal cell carcinoma, colorectal adenocarcinoma, hepatocellular carcinoma, and papillary carcinoma of the thyroid (p < 0.05). In pTa urothelial carcinomas, STING expression was associated with low-grade carcinoma (p = 0.0002). Across all tumors, STING expression paralleled PD-L1 positivity of tumor and inflammatory cells (p < 0.0001 each) but was unrelated to the density of CD8+ lymphocytes. STING expression is variable across tumor types and may be related to aggressive tumor phenotype and PD-L1 positivity. The lack of relationship with tumor-infiltrating CD8+ lymphocytes argues against a significant IFN production by STING positive tumor cells.

Background/Objectives: Trefoil factor 1 (TFF1) plays a role in the mucus barrier. Methods: To evaluate the prevalence of TFF1 expression in cancer, a tissue microarray containing 18,878 samples from 149 tumor types and 608 samples of 76 normal tissue types was analyzed through immunohistochemistry (IHC). Results: TFF1 staining was detectable in 65 of 149 tumor categories. The highest rates of TFF1 positivity were found in mucinous ovarian carcinomas (76.2%), colorectal adenomas and adenocarcinomas (47.1–75%), breast neoplasms (up to 72.9%), bilio-pancreatic adenocarcinomas (42.1–62.5%), gastro-esophageal adenocarcinomas (40.4–50.0%), neuroendocrine neoplasms (up to 45.5%), cervical adenocarcinomas (39.1%), and urothelial neoplasms (up to 24.3%). High TFF1 expression was related to a low grade of malignancy in non-invasive urothelial carcinomas of the bladder (p = 0.0225), low grade of malignancy (p = 0.0003), estrogen and progesterone receptor expression (p < 0.0001), non-triple negativity (p = 0.0005) in invasive breast cancer of no special type, and right-sided tumor location (p = 0.0021) in colorectal adenocarcinomas. Conclusions: TFF1 IHC has only limited utility for the discrimination of different tumor entities given its expression in many tumor entities. The link between TFF1 expression and parameters of malignancy argues for a relevant biological role of TFF1 in cancer. TFF1 may represent a suitable therapeutic target due to its expression in only a few normal cell types.

Background: The glucocorticoid receptor (GR) regulates the transcription of thousands of genes. In cancer, both oncogenic and tumor suppressive roles of GR have been proposed. Methods: A tissue microarray containing 18,527 samples from 147 tumor (sub-)types and 608 samples from 76 normal tissue types was analyzed for GR expression by immunohistochemistry. Results: GR positivity was found in 76.4% of 14,349 interpretable cancers, including 18.5% with weak, 19.6% with moderate, and 38.3% with strong positivity. GR positivity appeared in all 147 tumor types, with at least one strongly positive tumor in 136 types. Of out tumor entities, 77 of the 147 showed GR positivity in 100% of the cases analyzed. Only six tumor types had less than 50% GR-positive cases, including adenomas with low-/high-grade dysplasia (32.5%/21.7%), adenocarcinomas (17%) and neuroendocrine carcinomas (45.5%) of the colorectum, endometrial carcinomas (25.6%), and rhabdoid tumors (25%). Reduced GR staining was associated with grade progression in pTa (p < 0.0001) and with nodal metastasis in pT2-4 (p = 0.0051) urothelial bladder carcinoma, advanced pT stage (p = 0.0006) in breast carcinomas of no special type (NST), and high grade (p = 0.0066), advanced pT stage (p < 0.0001), and distant metastasis (p = 0.0081) in clear cell renal cell carcinoma. GR expression was unrelated to clinico-pathological parameters in gastric, pancreatic, and colorectal adenocarcinoma, and in serous high-grade carcinoma of the ovary. Conclusions: GR expression is frequent across all cancer types. Associations between reduced GR expression and unfavorable tumor features in certain cancers suggest that the functional importance of GR-regulated genes in cancer progression depends on the cell of tumor origin.

Background: TROP2 (TACSTD2) is a therapeutic target of antibody–drug conjugates and is broadly expressed in epithelial malignancies. Data on TROP2 protein expression in large, clinically annotated prostate cancer cohorts, particularly in recurrent disease, remain limited. Methods: TROP2 immunohistochemistry was performed on a prostate cancer tissue microarray comprising 17,747 primary radical prostatectomy specimens and 258 recurrent prostate cancer samples. TROP2 staining data were compared with clinicopathological parameters, biochemical recurrence and ERG status. Results: Among 12,807 interpretable primary prostate cancers, TROP2 staining was detectable in all cases and considered strong in 94.5%, moderate in 3.5%, and weak in 2.0%. Reduced TROP2 was statistically associated with high pT stage (p = 0.0011) and high Gleason grade (p < 0.0001), but absolute differences were small. Reduced TROP2 expression levels were unrelated to PSA recurrence in the entire cohort (p = 0.0787) but statistically linked to early PSA recurrence in ERG positive cancers (p = 0.0165). In four different scenarios of multivariate analyses, reduced TROP2 expression did not show an unequivocal independent prognostic role. As compared to primary tumors, TROP2 was markedly reduced among 250 evaluable recurrent cancers (strong 57.6%, moderate 31.6%, weak 8.4%, negative 2.4%; p < 0.0001 vs. primary cancers). Reduced TROP2 was also significantly more frequent in recurrent cancers than in the subgroup of high-grade primary tumors (Gleason ≥ 4+4; strong 57.6% vs. 90.2%; p < 0.0001). Conclusions: TROP2 is consistently expressed at high levels in primary prostate cancer but often reduced in recurrent disease. While uniform expression in primary tumors supports TROP2 as a therapeutic target in prostate cancer, reduced expression in many recurrent cancers highlights the potential need for TROP2 expression measurement as a predictive test in this subgroup.