Molecular Evaluation of Endometrial Dedifferentiated Carcinoma, Endometrioid Carcinoma, Carcinosarcoma, and Serous Carcinoma Using a Custom-Made Small Cancer Panel

Abstract

It is often difficult to histologically differentiate among endometrial dedifferentiated carcinoma (DC), endometrioid carcinoma (EC), serous carcinoma (SC), and carcinosarcoma (CS) due to the presence of solid components. In this study, we aimed to categorize these carcinomas according to The Cancer Genome Atlas (TCGA) classification using a small custom-made cancer genome panel (56 genes and 17 microsatellite regions) for integrated molecular diagnosis. A total of 36 endometrial cancer cases with solid components were assessed using IHC, next-generation sequencing (NGS), and the custom-made panel. Among 19 EC cases, six were categorized as MMR-deficient (MMR-d) and eight were classified as having a nonspecific molecular profile. Three EC cases were classified as POLE mutation (POLEmut)-type, which had a very high tumor mutation burden (TMB) and low microsatellite instability (MSI). Increased TMB and MSI were observed in all three DC cases, classified as MMR-d with mutations in MLH1 and POLD1. Except for one case classified as MMR-d, all SC cases exhibited TP53 mutations and were classified as p53 mutation-type. SC cases also exhibited amplification of CCND1, CCNE1, and MYC. CS cases were classified as three TCGA types other than the POLEmut-type. The IHC results for p53 and ARID1A were almost consistent with their mutation status. NGS analysis using a small panel enables categorization of endometrial cancers with solid proliferation according to TCGA classification. As TCGA molecular classification does not consider histological findings, an integrated analytical procedure including IHC and NGS may be a practical diagnostic tool for endometrial cancers.

Keywords: endometrial cancers; integrated molecular diagnosis; microsatellite instability; solid proliferation; tumor mutation burden.

FIGURE 1

Representative histology and IHC of p53 and MMR proteins. Representative HE sections from G2 EC (no. 2) showing well differentiated glandular and less differentiated solid areas. A few p53-positive tumor cells are observed, indicating wt p53 expression. All four MMR proteins are diffusely positive. The dedifferentiated part of DC (no. 22) exhibits wt p53 expression pattern and loss of MLH1 and PMS2 expression. Stromal lymphocytes also show a positive reaction as an internal control. The sarcomatous element of CS (no. 34) shows diffuse staining for p53 and all four MMR proteins. SC (no. 29) shows complete loss of p53 expression in both glandular and solid elements. The MMR protein expression is well preserved. CS, carcinosarcoma; SC, serous carcinoma; HE, hematoxylin and eosin (Original magnification: ×200); IHC, immunohistochemistry. (Original magnification: p53 × 400, MMR ×200).

FIGURE 2

Values of MSI and TMB in endometrial cancers. (A) The MSI (left panel) and TMB (right panel) scores of MMR-d EC cases are significantly higher than those of EC cases that are MMR-p. (B) The MSI and TMB scores of endometrial cancers are plotted as a scattergram, showing clear distinction of MMR-p (blue dot) and MMR-d cases (red dot), and TMB-ultrahigh POLE mutation cases (green dot). MMR, mismatch repair; MSI, microsatellite instability; TMB, tumor mutation burden; MMR-p, mismatch repair-proficient; MMR-d, mismatch repair-deficient.