Abstract: This invention provides a method for studying chromosomal gains and losses in cells from nipple aspirate fluid comprising the steps of: (1) aspirating fluid from breasts; (2) placing the samples of fluid obtained in step 1 onto dishes containing conditioned medium composed of a mixture of (a) supernatant from immortalized mammary epithelial cells and (b) mammary epithelial growth medium; (3) incubating the product of step 2 in a humidified incubator; (4) replenishing the medium in the dishes prepared in step 2 at regular intervals to maintain cell growth; (5) isolating the cells from the cultures; (6) preparing DNA from these cells; (7) amplifying the DNA; (8) labeling an aliquot of the amplified DNA; and (9) evaluating the labeled DNA for evidence of chromosomal gains or losses.