To assess Fgfr2ΔE18 oncogenicity in mammary tumour models representative of different breast cancer subtypes—including invasive lobular carcinoma, a hallmark of which is E-cadherin loss29—we intraductally delivered Fgfr2 variants to wild-type (WT) or Wap-cre;Cdh1F/F mice. Here, FGFR2 is linked to invasive lobular breast carcinoma.