Yes, it is possible it could be breast cancer. It could also be related to something else entirely.
The swelling may have indicated an allergy to the deodorant, but the lump
... there is only one. Maybe a cyst, an ingrown hair, an injury to that breast. I don't know. Swollen lymph glands point to something else. Maybe its related to puberty??
It wouldn't hurt to get this checked out by your doctor.