Quantitative analysis of lung metastases in mouse cancer models can be troublesome, often requiring laborious tissue sectioning. In a B16F10 melanoma cell colonization model, cells were injected into tail veins of mice and their lungs collected after two weeks. The left lung lobes were processed, optically cleared, and scanned in 3D using optical projection tomography. This provided a novel method to accurately quantify the volume and number of melanoma cell colonies from whole mouse lungs. For details, see the article by Kapiainen and colleagues on page 129.