Noticed lump on penis

  Last week when showering I noticed a lump on the shaft of my penis.  This seemed to appear suddenly,( one day ).  It is not painful.  It stands out prominately during erection.  It is a very hard knot, no discoloration, redness or other swelling.  Any suggestions as to what this may be?  Thank you in advance for any help you may offer.
--------------------------------------------------------------------------------------------------------------------------------
Dear R Bell,
The firm lump you describe on the shaft of your penis may be a plaque that is felt under the skin and associated with Peyronie