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

Introduction: 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.

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

Results: 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.

Conclusion: 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.