Watching cancer begin: emerging tools to visualize the first steps of tumorigenesis

Understanding tumor initiation is crucial for early interception and prevention. Tumors arise from genetic alterations and microenvironmental changes that together create a niche for malignant growth. Previously, the spatiotemporal dynamics of tumorigenesis were difficult to study. Recent advances in high-resolution intravital microscopy, tissue clearing, and spatial molecular profiling enable direct visualization of mutated cells and clones within their microenvironment in situ. These tools transform tumor initiation from a theoretical construct into a mechanistically dissectible process. Here, we synthesize recent insights into how mutated clones expand or regress, how clonal dynamics drive transformation, and how niche signals shape tumor-initiating cell fate. We highlight key imaging innovations and outline limitations and opportunities for capturing tumor initiation in vivo.