What Causes Excessive Vaginal Bleeding?

cousin of mine went to the dr.s apt had a cist not sure if it was outside r inside of her virgina . Anyhow they did a biopsy and had told her it was some sort of cancer. we just got a call from her boyfriend said that she had to be rushed to hospital. (and she was at work at the time ). Because she started cramping and bleeding heavy . wut could be the cause of this