“…For example, tracking of photoswitched mammary tumour cells showed that, compared with primary tumour cells distant from blood vessels, cells in close proximity to blood vessels migrate extensively within and outside of the primary tumour, and later on, are also detectable at secondary sites (Kedrin et al, 2008). Similarly, genetically engineered murine and patient-derived colon organoids that express known mutational drivers of colorectal cancer progression and metastasis were longitudinally tracked following photoswitching to define the cumulative mutational load required for tumour cell migration and subsequent metastasis (Fumagalli et al, 2017). This study demonstrated that a combined mutational load affecting several signalling pathways allows colorectal cancer ; LSL-tdTomato mice; here, low-level recombination of the tdTomato allele was used to label individual crypts with tdTomato (tdTomato, red; EGFP, green; scale bar: 20 μm).…”