It can also be an extra breast tissue that is growing.
Hi
Welcome to the MedHelp forum!
A lump that is getting larger could be a lymph node, a cyst, a lipoma or an abscess deep within. In males chances of breast cancer are less but should not be ignored. Ideally you should consult a surgeon for your son. However you can go to the PCP and maybe get a CT scan for the lump followed by a surgeon’s appointment.
Hope this helps. Please let me know if there is any thing else and do keep me posted. Take care!