Hi,
According to the doctors who examined you, this excessive breast tissue in your armpit is called “ Axillary tail of Spencer" This is not cancer but just normal breast tissue that extends upward toward the axilla area. Usually these types of lumps are left alone, but they can be surgically removed if they become too large or painful.
If you haven’t seen a Breast Specialist, I would advise you to do so. The specialist will be able to make recommendations for further evaluation.
Best wishes..