Relaxin 2 is a polypeptide hormone structurally related to insulin and insulin-like growth factors (IGFs). However it does not interact with insulin receptors and has a decidedly different biological properties. Relaxin 2 activates LGR 7 and LGR 8 relaxin receptors, that belong to the leucine-rich repeat-containing (LRR), G protein-coupled receptors. The characteristic functions of relaxin are associated with female reproductive system, especially during pregnancy. However recent studies have shown that polypeptides with relaxin-like factor family (RLF) are involved in cell proliferation and differentiation, as well as invasion and angiogenesis of female and male reproductive cancers. This review provides information on the structure and function of relaxin and its receptors. Furthermore, we present evidence of the involvement of these elements in the process of cancerogenesis.