Breast cancer. Multiphoton micrograph of breast cancer tissue using endogenous fluorescence. This image was obtained without using fluorophores, stains, or dyes, with the colours seen here due to the metabolic co-factors already inside the cells. A technique called second harmonic generation has made the collagen visible. This technique has important applications for patients who require label-free imaging. Tumour cells are cyan, macrophages are red, and collagen fibres are green. This tissue was from a live mouse model.