As stromal influences are likely to impact differently on subtypes of breast cancer (Wallace et al., 2011), it is important to consider the use of alternative site-specific recombinases (Olorunniji et al., 2016) to direct the stromal gene modification (e.g. Flp/Frt), which would permit investigation with the many available Cre/loxP GEMMs. Here, FLT1 is linked to breast carcinoma.