mastitis or breast cancer?

I am a 42 year old male. When I think back, I have felt a lump under my left nipple for some time. It didn't hurt so I didn't think anything of it. Several days ago, I bumped my chest and felt pain under my left nipple. I told my general doctor about this. My doctor told me I have mastitis in my left breast and put me on antibiotics. I have looked up mastitis and found information only pertaining to women and cows. I know breast cancer for men is very rare. I just want to be sure it is only mastitis. I don't want to loose another three weeks to see if the antibiotics don't work and then have to do other tests. What are the differences in symptoms between mastitis and breast cancer? How can I be sure I have mastitis? Is waiting three weeks not going to make much difference? Please ease my mind or let me know if I should pursue other avenues now.

[CCF-RN,MSN-rf]

Dear man1963:  Mastitis is an inflammation of the breast tissue.  It is most common in women (many times during breast feeding) and will usually clear with antibiotics.  Symptoms of mastitis may include pain, redness, swelling and warmth to touch.  If it does not resolve with antibiotics, then further investigation is necessary.  Breast cancer in men is uncommon but happens nonetheless.  If you feel a descrete lump under your nipple that has not gone away or has gotten larger, it needs to be evaluated, regardless of whether there is pain or not.  If you are concerned, consider a second opinion with a breast specialist, these people can often be located at large teaching institutions.

[surgeon]

mastitis is indeed very rare in a male, and if there wasn't redness, it's unlikely that that's what it was or that antibiotics will help. When there's a lump, it needs evaluation. In the vast majority of cases in males, especially younger than 60 or so, it turns out to be benign; gynecomastia, which means enlargement of male breast tissue. It can occur from certain meds, marijuana use, rarely certain hormone problems, and most often there's no particular reason. It just happens. Most general surgeons would have expertise to decide whether it needs biopsy or not. If so, it's usually a minor operation, often done under local, even as an office procedure.