Soft fibrin gels can promote the growth of tumorigenic cells from a pool of cancer cells, reports a study published online this week in Nature Materials. Injection of just a few of the gel-promoted cells in wild-type mice led to the formation of tumours in their lungs, suggesting that this approach to selecting tumorigenic cells could help the study of the mechanisms underlying the capacity of some cancer cells to produce tumours and to spread to distant organs.

The identification of cancer cells with tumorigenic potential has so far relied on the expression of stem-cell markers, which is often inaccurate. Ning Wang, Bo Huang and colleagues report a much more efficient and robust method for selecting tumorigenic cells. They demonstrate that a subset of cells from mouse or human cancer cell lines cultured in low-stiffness gels made of fibrin - a fibrous protein involved in blood clotting - grew more rapidly into bigger round colonies, and that a few of the cells extracted from the colonies formed tumours in both genetically identical and immunodeficient mice at the site of injection or in the lungs much more efficiently than cells cultured on top of the soft fibrin gels, on plastic dishes, or within soft collagen gels of similar stiffness.