Vaginal Squamous Cell Carcinoma Develops in Mice with Conditional Arid1a Loss and Gain of Oncogenic Kras Driven by Progesterone Receptor Cre

Oncogenic KRAS mutations are a common finding in endometrial cancers. Recent sequencing studies indicate that loss-of-function mutations in the ARID1A gene are enriched in gynecologic malignant tumors. However, neither of these genetic insults alone are sufficient to develop gynecologic cancer. To determine the role of the combined effects of deletion of Arid1a and oncogenic Kras, Arid1a(flox/flox) mice were crossed with Kras(Lox-Stop-Lox-G12D/+) mice using progesterone receptor Cre (Pgr(Cre/+)). Histologic analysis and immunohistochemistry of survival studies were used to characterize the mutant mouse phenotype. Hormone dependence was evaluated by ovarian hormone depletion and estradiol replacement. Arid1a(flox/flox); Kras(Lox-Stop-Lox-G12D/+); Pgr(Cre/+) mice were euthanized early because of invasive vaginal squamous cell carcinoma. Younger mice had precancerous intraepithelial lesions. Immunohistochemistry supported the pathological diagnosis with abnormal expression and localization of cytokeratin 5, tumor protein P63, cyclin-dependent kinase inhibitor 2A, and Ki-67, the marker of proliferation. Ovarian hormone deletion in Arid1a(flox/flox); Kras(Lox-Stop-Lox-G12D/+); Pgr(Cre/+) mice resulted in atrophic vaginal epithelium without evidence of vaginal tumors. Estradiol replacement in ovarian hormoneedepleted Arid1aflox/flox; Kras(Lox-Stop-Lox-G12D/+) :Pgr(Cre/+) mice resulted in lesions that resembled the squamous cell carcinoma in intact mice. Therefore, this mouse can be used to study the transition from benign precursor lesions into invasive vaginal human papillomaviruseindependent squamous cell carcinoma, offering insights into progression and pathogenesis of this rare disease.