A 38-year-old patient went to a women's clinic with complaints of moderate bleeding discharge from the genital tract, which occurred after the delay of the next menstruation for 1.5 months. During the vaginal examination revealed: the cervix is not eroded, the symptom of "pupil" (+++); the uterus is not enlarged, dense, mobile, painless; appendages on both sides are not enlarged, painless; the vaults are deep. Which diagnosis is most likely?