Lipoma On Back Of Ribs Costal Chondral Junction?

Costal Chondral Junction? - lipoma on back of ribs

I recently went to the doctor for his opinion on a painless mass in the chest and side bottom of my sternum and above and beside my xiphoid process. He felt, and he said he did not know, such as cancer or a lipoma feel, but because of my age (15) and growth of the breast, probably had a rib cartilage junction. Basically, an inflammation of the ribs meet my cartilage in my chest. I had a lump about a month, and want to learn more about the rib chondral junctions. I tried google, but could not find anything relevant to my problem.

So does anyone know how common is it? Is it likely that might have led to the development or cracking my back? Wil it disappears by itself? Anytihng monitor or should I do to help tSwelling? (This is only slightly higher significant but) the size of a quarter in diameter. Please share any information you can about it. Thank you very much:)