Sores won't heal

i just joined this forum today looking for advice on sores that won't heal. Had reconstruction after mastectomy last november. I developed what I thought was a rash on the underside of the reconstructed breast. I thought it was from having to wear a bra 24/7. Turns out it was not a rash, but recurrence of the breast cancer. Since then, I have been on oral chemo. The rash-like bumps have gotten worse and are open sores in some places. My onc sent me to wound care dr but he has not been able to find anything that helps; 5 different topical treatments since February and no u improvement. Is anyone familiar with this particular condition?  Wound dr said it was because of previous radiation that the sores won't heal but last summer I had an injury on my big toe and it took about 4 months to heal. No radiation in that area...