Our objective was to determine the temporality of BC exposure on DNA methylation of genes and loci previously implicated in urban asthma and/or allergic sensitization (e.g., interleukin 4 (IL4), interferon gamma (IFNγ), inducible nitric oxide synthase (iNOS encoded by NOS2A), and arginase2 (ARG2)) [11, 12, 25–32] (Additional file 1: Figure S1) and how it may vary by seroatopy and cockroach sensitization. This evidence concerns the gene NOS2 and breast cancer.