Clinicopathologic Characteristics of Trop Family Proteins (Trop-2 and EpCAM) in Gastric Carcinoma

Abstract

Purpose: Trop family proteins, including epithelial cell adhesion molecule (EpCAM) and Trop-2, have garnered attention as potential therapeutic and diagnostic targets for various malignancies. This study aimed to elucidate the clinicopathological significance of these proteins in gastric carcinoma (GC) and to reinforce their potential as biomarkers for patient stratification in targeted therapies.

Materials and methods: Immunohistochemical (IHC) analyses of EpCAM and Trop-2 were performed on GC and precancerous lesions, following rigorous orthogonal validation of the antibodies to ensure specificity and sensitivity.

Results: Strong membranous staining (3+) for Trop-2 was observed in 49.3% of the GC cases, whereas EpCAM was strongly expressed in almost all cases (93.2%), indicating its widespread expression in GC. A high Trop-2 expression level, characterized by an elevated H-score, was significantly associated with intestinal type by Lauren classification, gastric mucin type, presence of lymph node metastasis, human epidermal growth factor receptor 2-positivity, and Epstein-Barr virus (EBV)-positivity. Patients with a high Trop-2 expression level exhibited poorer survival outcomes on univariate and multivariate analyses. High EpCAM expression levels were prevalent in differentiated histologic type, microsatellite instability-high, and EBV-negative cancer, and were correlated with high densities of CD3 and CD8 T cells and elevated combined positive score for programmed death-ligand 1.

Conclusions: These results highlight the differential expression of Trop-2 and EpCAM and their prognostic implications in GC. The use of meticulously validated antibodies ensured the reliability of our IHC data, thereby offering a robust foundation for future therapeutic strategies targeting Trop family members in GC.

Keywords: Antibody specificity; Immunohistochemistry; Molecular pathology.

Fig. 1. Representative image of GC tissue immunostained for Trop-2 (A-H), EpCAM (I-P), CD3 (Q), CD8 (R), and PD-L1 (S, T). (A) Weak expression of Trop-2 in the nonmetaplastic foveolar epithelium. (B) Negative expression in metaplastic glands. (C) Moderate expression in low-grade adenoma; (D) Moderate expression in high-grade adenoma. (E) GC with strong Trop-2 expression. (F) GC with moderate expression. (G) GC with weak expression. (H) GC negative for Trop-2 expression. (I) Negative expression of EpCAM in the nonmetaplastic foveolar epithelium. (J) Strong expression in metaplastic glands. (K) Strong expression in low-grade adenoma. (L) Strong expression in high-grade adenoma. (M) GC with strong EpCAM staining; (N) GC with moderate staining. (O) GC with weak staining. (P) GC negative for EpCAM expression. (Q) GC with a high density of CD3+ cells. (R) GC with a high density of CD8+ cells. (S) PD-L1-positive carcinoma cells. (T) PD-L1-positive stromal cells.

GC = gastric carcinoma; EpCAM = epithelial cell adhesion molecule; PD-L1 = programmed death-ligand 1.

Fig. 2. Expression profiling of Trop-2 and EpCAM. (A) Trop-2 and EpCAM expression in nonmetaplastic gastric glands, metaplastic glands, low-grade adenoma, high-grade adenoma, early cancer, and advanced cancer specimens. (B) Distribution of Trop-2 and EpCAM expression in 412 gastric carcinoma cases.

EpCAM = epithelial cell adhesion molecule.

Fig. 3. Survival curves illustrating the survival differences and their significance. (A) Survival curves comparing all patients across various pathological stages (red, stage I; green, stage II; blue, stage III; violet, stage IV). (B) Survival curves comparing all patients based on Trop-2 expression levels (blue, low expression; red, high expression). (C) Survival curves comparing stage I, II, and III patients based on the Trop-2 expression level. (D) Survival curves comparing stage IV patients based on the Trop-2 expression level. (E) Survival curves comparing all patients based on the EpCAM expression level. (F) Survival curves comparing all patients based on the CD8+ cell density (blue, low density; red, high density).

EpCAM = epithelial cell adhesion molecule.

Fig. 4. Distribution of major molecular markers of gastric carcinoma. (A) Venn diagram illustrating the distribution of Trop-2, PD-L1, HER2, microsatellite instability MSI, and EBV status. (B) Survival curves depicting the poorer survival outcomes of 68 cases (red line) identified as Trop-2-high, but negative for all 4 molecular markers (white color area of A). The blue line denotes the remaining 344 cases.

EBV = Epstein–Barr virus; PD-L1 = programmed death-ligand 1; HER2 = human epidermal growth factor receptor 2; MSI = microsatellite instability.