Roundabout homolog 1 belongs to the neural adhesion molecule (NCAM) family of receptors. It is a receptor for SLIT1 and SLIT2 which are thought to act as a molecular guidance cue in cellular migration, including axonal navigation at the ventral midline of the neural tube and projection of axons to different regions during neuronal development. It may be required for lung development. There are three named isoforms. It is widely expressed, with the exception of kidney. Defects in Roundabout homolog 1 may be a cause of breast and lung cancer.