On my perineum i have a dark, hard purple vein? hurts when touched. app 1 inch long and in the middle a bubble that's app 1/4 in. is it cancer?

Thrombus: That's my diagnosis without seeing you. If it's not better in two weeks, have your physician check it out.

Hemorrhoids: This sounds like a hemorrhoid. You can try some conservative measures such as preparation H etc.. to see if it is relieved. If there is no improvment in a few days then you should see your doctor. While rare, anal cancer can often be confused with a hemorrhoid.

Vein?: Without looking at it, it sounds like it could be a varicose vein, which can be common in the perineal region. It's best to have it looked at by your gynecologist.