The MotHER Pregnancy Registry is a United States (U.S.)-based, prospective, observational cohort study in women with breast cancer who have been or are being treated with a trastuzumab (herceptin)-containing regimen with or without pertuzumab (perjeta) or ado-trastuzumab emtansine (kadcyla) during pregnancy or within 7 months prior to conception (regardless of cancer stage at the time of trastuzumab, pertuzumab, or ado-trastuzumab emtansine exposure).