Trop2 Expression in Correlation to the Molecular Subtype in Vulvar Squamous Cell Carcinomas

Targeted therapy with antibody-drug conjugates (ADCs) has achieved promising results in the treatment of different solid tumors. Sacituzumab-Govitecan (SG), a humanized anti-Trop2 monoclonal antibody linked with the cytotoxic topoisomerase I inhibitor SN-38, has been approved for the treatment of metastatic triple-negative breast cancer. The treatment approach with SG requires the expression of Trop2 within the tumor cells. Trop2 is overexpressed in many other cancer types, suggesting a broader therapeutic application beyond breast cancer to these ADCs. We explore expression of Trop2 vulvar squamous cell carcinomas (VSCCs) and how this relates to molecular classification.

Immunohistochemical Trop2 expression was evaluated on diagnostic biopsies of VSCC using an immunoreactive score. Staining results were compared to the molecular subtype of VSCC.

Fifty-seven cases were included in the study. 63.2% of VSCC were p16-ve/p53abn (HPV-independent (p53abn)) molecular subtype, 29.8% p16+ve/p53wt (HPV-associated) and 1.4% p16-ve/p53wt (HPV-independent (p53wt)) tumors. All diagnostic biopsies (N = 57) showed at least a weak Trop2 expression. Moderate and strong expression was seen in 15/17 (88.2%) of the p16-ve/p53abn, 32/36 (88.8%) of the p16+ve/p53wt and 3/4 (75%) of the p16-ve/p53wt molecular subtype. Expression was significantly higher, as assessed by H score, in the HPV-associated VSCC, compared to HPV-independent.

VSCCs have high expression of Trop2 and represents a promising therapeutic target. Clinical trials exploring Trop2-directed ADCs such as SG are warranted in this rare cancer type, including in the prognostically poor HPV-independent VSCC with a TP53-mutation (p16-ve/p53abn molecular subtype). The targetable molecule, Trop2, can be easily assessed by immunohistochemistry on diagnostic biopsies from VSCC.