hi,
Nothing scary symptom.
A lump under the arm (armpit) is mostly a lymph node which has various reasons for it too enlarge starting from a infection in the catchment(draining) areas.
Next possibility could be an breast mass itself - FIBROADENOMA
Hi,
Well having a family history of breast cancer puts you in the high risk group. Has the size of the lump changed since you last noticed it? Have you experienced any associated symptoms of nipple discharge etc? Lumpiness in the breasts is normal due to hormonal fluctuation during the mestrual cycle in females. Do you notice any association with your menstrual cycle? Well you need to get a clinical evaluation done at the earliest and also ask your physician for a screening mammogram and an USG for further evaluation. That should put all doubts to rest and would also help to identify the lesion. Dont worry most lumps are not cancerous but they still need to be investigated to be absolutely certain. Goodluck.