Final answer:
The most likely diagnosis based on the pelvic examination findings described is cervical cancer.
Step-by-step explanation:
Based on the findings of dark red blood in the posterior vaginal vault and a 3-cm friable mass on the ectocervix, the most likely diagnosis is cervical cancer. Cervical cancer often presents with vaginal bleeding, especially after sexual intercourse, and can be associated with the presence of a mass on the cervix. The friable nature of the mass suggests that it easily bleeds when touched, which is a characteristic of cervical cancer.
Dark red blood in the posterior vaginal vault refers to bleeding coming from the cervix and pooling in the back part of the vagina, which is a common feature of cervical cancer.
To confirm the diagnosis, further investigations like Pap smear, colposcopy, and biopsy may be necessary. Treatment options for cervical cancer include surgery, radiation therapy, and chemotherapy.