In late stage tumours (D14 and D21), 3 of the 5 most abundant CAF subpopulations in both 4T1 and 4T07 tumours are CD26+ (Fig. 4), and we observe a trend towards an increase over time of CD26+ CAFs in 4T1 tumours, and a decrease over time of the same population in the less aggressive 4T07 tumours (Fig. 2), warranting further studies into the functional phenotype of these CD26+ CAF subpopulations. The gene discussed is DPP4; the disease is neoplasm.