This technique, coupled to a phospho-endogenous protein FLIM,27 shows cell-to-cell heterogeneity in EGFR activity within a basal-like breast cancer xenograft and a colorectal cancer model, which can be in part explained by a significant correlation between tumour cell EGFR activity and macrophage infiltration within the tumour microenvironment. The gene discussed is EGFR; the disease is colorectal cancer.