IIf it were me I would not be worried.
Hi,
If you have no other symptoms except this red spot,I would think that you could have a skin problem and nothing at all like breast cancer.There is not much we can tell you over the internet,because a red spot on the breast can occur like on any other part of your body and the causes are many.
This spot could be an allergic reaction to the material of a new bra,,soap, lotion etc...
If this does not go away and it continues to be of concern to you,please bring it to the attention of your doctor for a clinical breast exam for evaluation.You could also consult a dermatologist.
Take care....