In contrast, previous studies from our laboratory, comparing matched primary and metastatic lesions from the highly metastatic MMTV-PyMT mouse model of breast cancer, did identify reproducible metastasis-associated point mutations in Shc1 and Kras. These studies, however, were performed on a much more genetically homogeneous set of animals than is observed in the human population, suggesting that these potential metastasis driver mutations might only represent a small fraction of the patient population. This evidence concerns the gene KRAS and breast carcinoma.