The correlation between fibroblast IFNβ1 and tumour cell MX1 was strengthened in the claudin-low group (r = 0.375; p = 0.008) while it was lost in the claudin-high cohort (r = 0.113; p = 0.389), mirroring our tissue culture observations that claudin-low cancers are most receptive to CAF-induced IFN signalling. Here, IFNA1 is linked to cancer.