Although further studies are needed to identify causal genes in respective Mts-QTLs, the panel of candidate genes with reported gene expression changes or polymorphisms in breast cancer patients, Prlh for Mts-1, Anpep or Blm for Mts-2, Ece1 for Mts-3, and Smad2 for Mts-4_validate the hypotheses that these genes should be studied further in different experimental systems and in humans as potential susceptibility genes for mammary tumorigenesis. Here, SMAD2 is linked to breast cancer.