In keeping with a role for Arid1a in tumour morphology, loss of Arid1a also led to a reduction in luminal marker keratin 8 (Pb-Cre;Ptenfl/flArid1a+/+, histoscore of 77.3; Pb-Cre;Ptenfl/flArid1afl/+, histoscore of 56.8; Pb-Cre;Ptenfl/flArid1afl/fl, histoscore of 43.4) and an elevation in basal marker keratin 5 (Pb-Cre;Ptenfl/flArid1a+/+, histoscore of 18.8; Pb-Cre;Ptenfl/flArid1afl/+, histoscore of 21.7; Pb-Cre;Ptenfl/flArid1afl/fl, histoscore of 62.7) (Supplementary Fig. 3). Here, KRT5 is linked to neoplasm.