Could a 13 year old girl get breast cancer?

Very unlikely: While anything is possible, breast cancer in a teenager is almost unheard of. Pubertal breast nodularity is the most common finding. See her doctor for an examination.

< 1 in a Million: Breast cancer is very rare in women under 30 and increases in incidence the older you get. The statistical probabibility of having breast cancer at 14 is less than the probability of winning a million dollars in the lottery. A breast lump in a teenaged girl is most likely a benign fibroadenoma, which can be confirmed by ultrasound +/- biopsy.