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The lump described can be either a growth of excess scar tissue or due to presence of infection and collection of pus in the incision site.
In case, the lump is a increased scar tissue, observation for a few weeks might see a gradual decrease in the scar tissue due to gradual absorbtion. Injection of steroid injections may also be an option, which can be decided by your doctor.
In case of possible infection and collection of pus, the wound may need debridement, drainage of pus, along with antibiotics and proper wound care.
You may consult with your operating surgeon or your doctor for additional information and proper help.