Hi,
It is hard to tell at this point if this is just an infection or something more serious.
I understand your concern, but we cannot be really sure until further evaluation is done.
I would suggest that you have this open sore examined by a Dermatologist or preferably a Breast surgeon and see what his/her opinion is.
This could be an infection. Anything that can happen on regular skin can happen on the skin of the breast.
I hope there is nothing there to worry about, but to be on the safe side it's best to let one of the physicians I mentioned above, figure it all out.
Best wishes…
Looks like a bacterial ecthyma settling down.May respond to external application of mupirocin.Do consult your doc.