CLDN3 positivity was most seen in neuroendocrine neoplasms (92–100%) and in adenocarcinomas (67–100%), tumors of the female genital tract, including various subtypes of ovarian and endometrial carcinoma (up to 100%), as well as different subtypes of breast cancer (95.3–100%). The gene discussed is CLDN3; the disease is endometrial carcinoma.