Based on the BRCA1 methylation patterns observed in the WHIM PDX series and in the PDX models derived from treatment-naïve or post-treatment patient cancers, we hypothesized that fully methylated BRCA1meth tumors would undergo demethylation after even short exposure to chemotherapy, resulting in restoration of BRCA1 expression and resistance to platinum. This evidence concerns the gene BRCA1 and cancer.