TROP-2 expression in germ cell tumors (GCT).

5031 Background: Trophoblast cell surface antigen 2 (TROP-2) is a tumor associated antigen overexpressed in several malignancies including breast and urothelial cancer. The TROP-2 antibody-drug conjugate (ADC) Sacituzumab govitecan is approved for treatment of metastatic breast cancer. The expression of TROP-2 in GCT is unknown. We present immunohistochemistry results of TROP-2 expression in GCT. Methods: Patients who underwent resection for GCT at Indiana University were included. Sixty formalin-fixed paraffin-embedded (FFPE) GCT samples were available. FFPE slides were selected from differing GCT histology and surgical sites including primary tumor, retroperitoneal lymph node, and distant metastases. Immunohistochemical (IHC) staining for TROP-2 (clone 1, mouse monoclonal, Enzo Life Sciences) was conducted and scored by intensity on a 0-3 scale by an experienced pathologist. Results: Samples from 60 individual specimens were available for IHC analysis. TROP2 expression was detected in 29 (48%) of these samples. Intensity expression differed from pure seminoma, mixed non-seminoma (NSGCT), teratoma, yolk sac tumor, and choriocarcinoma samples. Both primary and metastatic samples had TROP-2 expression of varying degrees. Conclusions: TROP-2 expression varies across histology in GCT. Seminoma appears to have the lowest expression of TROP-2. Higher TROP-2 expression was noted in choriocarcinoma and yolk sac tumor samples indicating potential as a target in these histologic subtypes in future clinical trials. Detectable TROP-2 by histology. Sample histology (N) Total detectable TROP-2 expression (%) 3+ 2+ 1+ Seminoma (20) 3 (15) 2 1 NSGCT (19) 12 (63) 9 (6*) 2* 1* Teratoma (9**) 6 (66) 3* 3* Yolk sac (9) 5 (56) 2 3 Choriocarcinoma (3) 3 (100) 1 1 1 *In epithelial elements of teratoma. **Three negative samples with only small fragments of teratoma and false negative may be present.