Is it possible for a 21 year old to get breast cancer?

Yes: Not too common but it can occur. Needs a doctor evaluation to tell what she may have.

Almost-never.: The statistical probability of getting breast cancer at 21 is lower than the odds of winning the lottery. Breast cancer rates increase the older you are, and are rarely seen before the 30's. However, if you have a palpable lump and/or a strong family history of breast or ovarian cancer, please see your primary care doctor or gynecologist.

Unlikely : Unlikely that a breast lump be malignant in a 21 year old but see your doctor for an evaluation as they will be the best judge of what is going on and give you appropriate advice.