Hi,
The chances that this is cancer are minimal.
The lump that you feel could be an axillary lymph node. These are known to enlarge secondary to shaving, waxing, using a new deodorant, due to infection or inflammation, etc.
Use some warm compresses and do not shave, wax or use a deodorant for a few days - the lump should resolve on its own.
Have you noticed any abnormal features on breast self examination like a breast lump, nipple discharge or skin changes?
If it still persists, you would need to see your surgeon for a clinical evaluation.
Let us know if you have any other doubts and keep us posted on how you are doing.
Regards.
Hi. You should probably go to a doctor and have it checked out - especially because of your family history. It would maybe put your mind at peace to see the doctor.