Epidermal hyperplasia during tissue inflammation was driven by FcεRI-signalling in basophils, and tumour growth also appeared to be promoted mainly by basophils, although we cannot exclude a role for mast cells because Cpa3Cre/+ mice (which lack mast cells and most basophils) were more protected from carcinogenesis than Mcpt8Cre/+ mice (which have normal mast cell numbers but lack most basophils). Here, FCER1A is linked to neoplasm.