Hi,
If you have no other symptoms except this red patch, I doubt that it has anything to do with breast cancer.The
skin of the breast is like
skin anywhere on the body and is subject to rashes, irritations, allergic reaction to the material of a new bra, soap, lotion etc...
If you notice that this problem is worsening and continues to be of concern to you, please bring it to the attention of your doctor for evaluation.You could also consult a dermatologist.
Take care....