IL17A and neoplasm: In particular, tumour-infiltrating TH17 cells have previously been associated with CRC progression.2 IL-17A itself has been implicated in tumour progression through STAT3 activation, promoting colonic epithelial cell transformation, tumour cell proliferation and invasion.4 Contrastingly, the presence of colorectal tumour-infiltrating TH17 cells was recently reported to correlate with improved survival,5 implying that IL-17A has important context and tissue-dependent roles in enacting pro- or anti-tumour immune mechanisms.6