MICROMETASTASIS development has been driven by quiescent disseminated tumour cells that suppressed immune surveillance and established an immune privileged environment, according to a multimodal study using mouse models and human metastatic samples. The analysis tracked disease progression from single disseminated tumour cells through to established lung metastases, providing a detailed view of the changing tumour microenvironment over time. The study identified a residual population of quiescent disseminated tumour cells with high phosphoglycerate dehydrogenase expression that survived initial innate immune clearance. These macrophages contributed to an immune privileged niche by recruiting immunosuppressive cells, further limiting immune surveillance during metastatic colonisation. Similarly, depletion of interstitial macrophages prevented formation of the immune privileged niche and reduced metastatic outgrowth.