breast cancer

my 17 years old has acyst on herr breast in aliittle over a month it has grown from unable to feel to the size of a quarter, they have only done an ultrasound. they say the likelyhood of it being cancer are slim because of her age. both my husband and i have lost parent early to cancer, his mother died of lumphnoma, my father lukemia. his mother had breast cancer a few years prior,but they say she died of lumphnoma. hie father also has adrenal cancer. when is appropiate to get a biosy

[Fernando Roque, MD]

Hi.  Your daughter's doctors are right in saying that the likelihood your daughter's breast lump will turn out as cancer is slim since she is quite young.  Breast lumps in her age group usually turn out to be benign conditions like fibrocystic disease or fibroadenoma.  However, given your strong family history of cancer, and the relatively fast growth of that mass (growing to the size of a quarter in 1 month), it might be better do some additional tests.  A mammogram would be a better screening procedure than breast ultrasound.  If that lump turns up to have a "suspicious" appearance on mammography, then getting a biopsy would be an appropriate next step.  If the mammography findings are benign or equivocal, repeating the mammogram after 4-6 months may be done.