mammogram test results

I had my mammogram today. All is well. Nothing cancerous. There's a hardening of the fat between my left pectoral muscle and the skin. The people at the xray center kept calling it a breast. I refuse to call my pecs breasts. Its a pec or a chest. I dont have breasts. They suggested I look into my diet to see if that was causing the hardening of the chest tissue. I've logged my food consistently for the last 70 days so investigating  my food history was easy. I just logged onto myfitnesspal. I couldn't find anything that could cause a hardening of the tissue. No soy, etc. I did read some articles on gaining and losing large amounts of weight. Not only can gaining and losing large amounts of weight cause hardening of the fatty chest tissues, but it's also extremely bad for the heart. And I've gained and lost a 100-150 pounds a bunch of times.