These differences underscore the heterogeneity among ovarian cancer cells and emphasize the importance of claudin-4 in modulating the response to PARP inhibitors in high-grade serous ovarian carcinoma, the most prevalent subtype of ovarian cancer, which accounts for more than 75% of all ovarian cancer cases (19, 22, 43). This evidence concerns the gene CLDN4 and ovarian serous carcinoma.