Blue veins on breasts. enlarged due to a tumor or something?

Not usually: Breasts have a relatively large blood supply, and it is not uncommon for veins to be visible through the skin. In vast majority of cases has nothing to do with anything abnormal. It is suggested you consult your gyn doctor and discuss at time of annual examination.

Not usually : Blue veins on the breast are not unusual and may be more visible with no tan or become more enlarged with pregnancy or breast augmentation. Rarely is it a sign of tumor. However, it has suddenly increased or is located on one breast more than another, it should be repeated to your physician.