What information could cancer researchers gain from using DNA microarrays?

DNA microarrays allow scientists to determine the genotype of a chunk of our genome and also measure the how the genes in that chunk are expressed. Using this technique has been essential in isolating genes that predispose people to cancers, and therefore allowing physicians to preemptively identify and monitor at-risk individuals. For instance, the genes BRCA1, BRCA2, and PALB2 have all been identified (using DNA microarrays) and linked to breast cancer. Knowing this allows individuals to seek out testing and take appropriate measures to prevent cancer/monitor the possible onset of cancer, which has proven to be life-saving.