A hardened lump could be just dead tissue, an enlarged or infected gland, or breast cancer
. Only examination by your doctor, with a mammogram and ultrasound will give you an idea of what it is, and a doctor would probably want to do a fine needle biopsy just to be sure whether it is cancer or not. 80% of lumps are benign.
I am a 3yr cancer survivor, bilateral mastectomy, 2 rounds reconstruction. No chemo, no radiation, oral chemo will total 5 years. Side effects difficult but doable.