Hi I just had a new set of mammograms on my right breast. After doing a ultrasound too, the Dr. came in and also use the ultrasound. He said I have a cyst that in six months I will have a mammogram and probably ultrasound to see if it has grown. I am not sure if it sebaceous but is that what you have? I have not been wearing a bra while at home (I am retired). But when I do put my bra on I spray a natural deodorant under my breast, so since I have never had cysts anywhere in my body, I am thinking this caused it and I will stop using it.