Kianoosh Keyhanian

Dominant Negative PTEN Alterations in Endometrial Carcinoma Are Associated With Retained Immunohistochemical PTEN Expression

PTEN immunohistochemistry (IHC) is considered complimentary for assessment of PTEN abnormality in endometrial carcinoma (EC), since PTEN IHC staining pattern does not entirely correlate with the presence and absence of mutations on sequencing. A set of functionally defective PTEN variants with stable protein levels are known to act in a dominant-negative manner to suppress wild-type PTEN activity. Our objective was to evaluate PTEN IHC patterns in ECs with dominant-negative (DN) PTEN mutations. ECs with next-generation sequencing (NGS, using Oncomine Comprehensive Assay v3) over a 3-year period were enrolled. PTEN IHC was scored as loss, subclonal loss, reduced, and intact (the last 3 considered retained). Of 182 EC cases, 114 (62.6%) were identified to have PTEN mutation(s), the majority of endometrioid histotype (87.7%) from all EC molecular classes. Forty-seven cases (41.2%) harbored DN mutations which were of endometrioid (FIGO 1 [n=15, 31.9%], FIGO 2 [n=23, 48.9%], FIGO 3 [n=3, 6.4%]), dedifferentiated (n=2, 4%), carcinosarcoma (n=3, 6%), mixed endometrioid and clear cell carcinoma (n=1, 2%) histotype; with representatives from all molecular classes. PTEN IHC showed retained expression in 95.8% (45/47) of DN-mutated cases (intact staining in 36 [76.6%], reduced staining in 6 [12.5%], and subclonal loss in 3 [6.4%]) cases. Two cases showed loss of expression (4.2%). In the PTEN wild-type group, loss and subclonal loss of expression were seen in 12.5% and 9.4%, respectively. Our results indicate that DN PTEN mutations are common in EC, and are associated with retained IHC staining (intact, reduced, or subclonal loss). These results highlight that IHC and NGS are both required in capturing the full spectrum of PTEN-abnormal EC.

Nuclear β-Catenin Expression in the Context of Abnormal p53 Expression Indicates a Nonserous Histotype in Endometrial Carcinoma

The interobserver reproducibility is poor for histotyping within the p53-abnormal molecular category of endometrial carcinomas (ECs); therefore, biomarkers that improve histologic classification are useful. β-catenin has been proposed to have prognostic significance in specific clinicopathologic and molecular contexts. The diagnostic utility for β-catenin expression patterns in determining the histotype of p53-abnormal ECs has not been well studied. We identified ECs molecularly classified as “p53-abnormal.” The p53-abnormal classification was assigned when (1) no POLE exonuclease domain hotspot mutations identified, (2) mismatch-repair protein expression was retained, and (3) abnormal p53 expression (null or overexpression) was present. Morphology was re-reviewed and β-catenin immunohistochemistry was scored as abnormal (nuclear) or normal (membranous, non-nuclear). Eighty ECs were identified in the “p53-abnormal” category; 27 (33.75%) were uterine serous carcinomas, and 53 were of nonserous histotype: 28 uterine carcinosarcomas (35%), 16 endometrioid carcinomas (20%), 2 clear cell carcinomas (2.5%), and 7 high-grade EC with ambiguous morphology (8.75%). All 27 uterine serous carcinomas demonstrated membranous β-catenin staining. Of the 53 nonserous ECs, 11 (21%) showed abnormal β-catenin expression: 6 endometrioid carcinomas, 4 uterine carcinosarcoma, and 1 high-grade EC with ambiguous morphology. The specificity of abnormal β-catenin expression for nonserous EC is high (100%) but the sensitivity is low (21%) with positive and negative predictive values of 100% and 60%, respectively. Our data shows that abnormal β-catenin expression in the context of p53-abnormal EC is highly specific, but not sensitive, for nonserous ECs and may be of value as part of a panel in classifying high-grade EC, particularly to exclude uterine serous carcinoma when nuclear staining is present.