Lung cancer metastasis. Fluorescence light micrograph of lung cancer cells spreading to invade surrounding tissues, a process called metastasis. These lung cancer cells have a mutation of a gene called LKB1 (green) that promotes invasion. Actin, a cytoskeletal protein, is shown in red, while cell nuclei are blue. These H157 lung cancer cells are expressing a green fluorescent protein (GFP)-tagged piece of an antigen called liver kinase B1 (LKB1), disrupting the normal function of this antigen. This experiment was carried out over 24 hours with a spherical cluster (spheroid) of these cells, embedded in a 3D collagen matrix.