It only appeared when the penis was erect and after sex, and had been left un-noticed until today. Like Steve, my bump has the ability to move around, but I cannot distinguish any tangled up veins or anything. I thought perhaps it was a cyst. I am relatively young, at 24, but have not discounted the fact that it may perhaps be Peyronie's disease. The mass, however, is invisible to the touch, and sight when the penis is limp.
Uncircumcised men are at increased risk.
HPV infection is also thought to be associated with penile cancer. Lesions are usually on the glans foreskin, or coronal sulcus, not the shaft of the penis. These may be tender and resolve spontaneously. Ibuprofen can help decrease the inflammation. If the lesions do not resolve, we would suggest evaluation by a physician.