Morules But Not Squamous Differentiation are a Reliable Indicator of CTNNB1 (β-catenin) Mutations in Endometrial Carcinoma and Precancers

Abstract

Although collectively regarded as "squamous differentiation (SD)" in endometrial endometrioid carcinoma (EEC) and atypical hyperplasia/endometrioid intraepithelial neoplasia (AH/EIN), morules (often referred to as "squamous morules") and true SD may represent two distinct phenomena. Here, we explored the distinction between morules versus SD and investigated the association of morules and SD with CTNNB1 mutations. A total of 270 cases of EEC and AH/EIN were studied, including EEC with (n = 36) or without (n = 36) morules and AH/ EIN with (n = 80) or without (n = 118) morules. Cases were analyzed by immunohistochemistry and selected cases (n = 20) by targeted next-generation sequencing panel. Near-perfect agreement was found between morules and glandular β-catenin nuclear staining in AH/EIN and EEC. A strong positive association was found between morules and glandular β-catenin nuclear staining (P < 0.0001, Φ = 0.59 in AH/EIN; P < 0.0001, Φ = 0.85 in EEC). There was no association between (1) morules and glandular PAX2 or PTEN aberrant expression or (2) SD and aberrant expression of β-catenin, PAX2 or PTEN (Φ = 0.09, β-catenin; Φ = 0.16, PAX2; Φ = 0.13, PTEN). CTNNB1 mutations were identified in all 20 selected morule-containing cases (100%). Next-generation sequencing was performed on 2 (preprogestin and postprogestin treatment) biopsies from 1 patient, revealing identical mutational profile in morules and glands. In conclusion, (1) SD and morules are distinct biological phenomena; (2) the presence of morules, but not SD, is a reliable indicator of CTNNB1 mutations in EEC and AH/EIN. Our findings demonstrate that SD and morules are distinct biological phenomena. Since morules but not SD are associated with β-catenin mutations, the distinction is clinically relevant and should be included in diagnostic reports.

Utility of a PAX2, PTEN, and β-catenin Panel in the Diagnosis of Atypical Hyperplasia/Endometrioid Intraepithelial Neoplasia in Endometrial Polyps

“…[34][35][36][37][38][39][40][41] Our previous study confirmed that morules are a reliable indicator of CTNNB1 (β-catenin) mutations in endometrial carcinoma and precancers. 10 Morules were absent in all EMPs included in this study. Rare cases of EMP with "squamous morules" or "morular metaplasia" have been reported in the literature.…”

“…In our cohort, criteria for the diagnosis of EMP includes either an intact polypod-shaped lesion or, when the lesion is fragmented, a combination of stroma, glands, and vasculature characteristic of EMPs. Interpretation of β-catenin, PAX2, and PTEN was performed as per our recent publications 9,11,18 . Due to the fact that sporadic loss of PAX2 and PTEN is observed in a small proportion of normal endometria (typically, in <10% of endometrial glands), the absence of staining for these markers in ≥5% of glands was considered loss of expression 9 .…”

“…Interpretation of β-catenin, PAX2, and PTEN was performed as per our recent publications. 9,11,18 Due to the fact that sporadic loss of PAX2 and PTEN is observed in a small proportion of normal endometria (typically, in <10% of endometrial glands), the absence of staining for these markers in ≥5% of glands was considered loss of expression. 9 The presence of strong, unequivocal nuclear β-catenin staining in any proportion of glands was interpreted as aberrant.…”

“…Recently, the World Health Organization 2020 Classification system for the first time recommended the incorporation of biomarkers into the diagnostic workflows for AH/EIN 3 . Our recent studies demonstrated the reliable identification of the majority of AH/EIN (92.8%) using an immunohistochemical (IHC) marker panel comprised of PAX2, PTEN, and β-catenin 9–13 . In this study, we systematically investigated the performance of the 3-marker panel (PAX2, PTEN, and β-catenin) in aiding the diagnosis of AH/EIN within EMP (AH/EIN in EMP) and other putative polypoid precancers.…”

β-catenin, Pax2, and Pten Panel Identifies Precancers Among Histologically Subdiagnostic Endometrial Lesions

“…The subsequent FIGO 1 adenocarcinoma, diagnosed 5 weeks later, was aberrant for Pax2, Pten, and β-catenin, and concordantly exhibited squamous metaplasia, commonly seen in CTNNB1 -mutant endometrioid adenocarcinomas. 22 , 23 , 33 Thus, this is another example of marker concordance in a precursor lesion that was diagnosed as NAH by histologic features, but in fact, is revealed by the 3-marker panel to be a neoplastic precursor mimicking a non-neoplastic process. It is also another example of the 3-marker panel’s ability to detect aberrancy even with suboptimal sampling (which seems likely in this case given the extremely short time interval between index and progressor).…”