Targeted Molecular and Immunohistochemical Analyses of Endometrial Clear Cell Carcinoma Show that POLE Mutations and DNA Mismatch Repair Protein Deficiencies Are Uncommon

Abstract

Endometrial clear cell carcinoma (ECCC) is an uncommon histotype without unique identified molecular alterations. Recently, The Cancer Genome Atlas molecular subtypes have been reported in ECCC. ECCC cases were collected from 11 institutions with diagnoses confirmed by morphologic review and immunohistochemistry. DNA mismatch repair (MMR) proteins, p53 expression, and ARID1A expression was assessed by immunohistochemistry on tissue microarrays. Targeted next-generation sequencing was completed for POLE, TP53, KRAS, and PIK3CA. Pathogenicity of mutations was determined using MutationTaster and PolyPhen databases. For p53, immunohistochemistry and sequencing were complimentarily used to assess the p53 status. Of 57 cases, 46 were considered prototypical ECCC by morphology and immunohistochemical profile (Napsin A-positive and ER-negative). Three cases were excluded because of insufficient sample for complete immunohistochemical analysis, and 6 had failed sequencing, resulting in 37 cases. Of the 37 remaining cases, 6/37 (16%) had predicted pathogenic mutations in the exonuclease domain of POLE with an allelic frequency >10%; however, no hot-spot mutations were identified. No cases were MMR-deficient. The gene most commonly affected was TP53 (59%, 22/37), followed by KRAS (13%, 2/15) and PIK3CA (13%, 2/15). The current study is the largest molecular analysis of pure ECCC reported to date. When strict classification criteria are applied, MMR-deficient and POLE mutated subtypes are not represented. Further consensus on what represents a deleterious POLE mutations is needed. The findings support separately studying histologically/immunohistochemically defined ECCC to identify characteristic molecular alterations in future studies.

Letter in response to: McAlpine J, Leon‐Castillo A, Bosse T. The rise of a novel classification system for endometrial carcinoma; integration of molecular subclasses. J Pathol 2018; 244: 538–549

“…Yet an important question is why are pathologists reluctant to use these tests for histotyping? For example, DeLair et al reported in another recent issue of this Journal that 6/32 (19%) pure endometrial clear cell carcinomas were mismatch repair‐deficient , which according to Drs McAlpine, Leon‐Castillo, and Bosse demonstrates “… ‘proof of concept’ that molecular classification may be clinically meaningful across all histotypes.” In contrast to this, we found no mismatch repair deficiency in a total of 51 pure endometrial clear cell carcinomas from two independent series that underwent immunohistochemical confirmation (Napsin A/HNF1β/ER) . Instead, we found a frequency of mismatch repair deficiency of 65% (27/41 cases) reported as ‘mixed endometrioid clear cell carcinoma’ .…”

Histological and molecular diversity and heterogeneity of precancerous lesions associated with inflammatory bowel diseases

“…The immunostaining results of the different markers were read and scored as described previously 21–25. For all of the markers, except PTEN and IMP3, a nuclear stain was expected to demonstrate their expressions.…”

Clear cell endometrial carcinoma and the TCGA classification

“…Study methods are reported in detail in the Data . Five studies with a total of 162 patients with CCC were included. The characteristics of the included studies are shown in Table .…”