Abstract: The present invention relates to a method for predicting the prognosis of breast cancer patients by using gene deletions and, more particularly, to: a method for detecting a marker for the prognosis of triple negative breast cancer patients in order to provide information necessary for the breast cancer prognosis diagnosis, comprising the steps of obtaining a sample of a subject, extracting genomic DNA from the sample, examining deletions of genes in the extracted genomic DNA, and determining that a subject, in which gene deletions in genomic DNA are confirmed, has a poor prognosis for breast cancer; and a composition for predicting the prognosis of breast cancer patients, containing a preparation enabling the examination of gene deletions and a kit comprising the same as an active ingredient.