Possible Male breast cancer or gynecomastia?

[Joe21]

I beleive (and hope)I have unilateral Gyne. Heres my story:

At around 15 I developed the "perfect round disc" under my right nipple (synonymous with Gyne.) it was there for about 3 months, this is disappeared, later reappeared under my right nipple, stayed there about a few months, then it dissappeared. So for awhile i was lump less, problably around 16 i developed a slightly bigger, not so smooth one underneath the left nipple. Im 21 right now and have had it ever since. I have slight puffyness in the left breast and the a disc like lump under my nipple. Its very much like a disc when you press against yourself and rub in a circular motion. I have no symptoms of cancer, no discharge bleeding, discoloration, no lumps under my arms, inversion of nipple. Anyway, the lump over the years has hurt on an off. not like a hurt as much as a little soreness, the surrounding area is somtimes sensitive. Its 90% painless unless I feel it awhile, then it feels a little sore. Im a healthly kid, active, I workout 3 times a week, never did any kind of drugs that would induce this,like steroids. Im also concerned because now when i take a deep breath and stretch my arms out, around where my lump is I feel a pain, from the lifting heavy weights maybe? its only when i take a deep breath in and stretch, it almost feels like a pulled muscle but it feels the same almost every time i do it and its been 3 weeks. so Ive had the lump for about 5 years now, ive moved locations several times, and went through several girlfriends, could this be a hormone imbalance I developed? or cause for concern?

[CCF-RN,MSN-JS]

Dear Joe21, It is unlikely that this mass is due to breast cancer.  Male breast cancer is rare, but one out of every 150 cases of breast cancer involves a man, usually in men over 60 years old.  Although a painless breast lump is the most common sign, most breast lumps in men are benign (non-cancerous) and are related to some other cause.  The first step in determining what the cause might be in your situation would be to have this checked out be a health care professional, they can ask questions and do an examination.

[surgeon]

What you describe sounds like gynecomastia, as you said. Male breast cancer, rare as it is, is almost unheard of at your age; and having had the lump for as long as you have, without significant change, makes it virtually certain it's not cancer. The soreness you describe sounds muscular; gynecomastia can be tender, but usually not exertion related. And the fact that it's a symmetrical, disc-like lump is also typical of gyncecomastia.  Of course, no online analysis can be considered accurate; the safest thing is to have it checked out.