The Janus Nature of Nanohydroxyapatite in Tumor Progression

Abstract Nanohydroxyapatite (nHAP) has broad applications because of its nanoscopical dimension, large specific surface area, biocompatibility, and low cytotoxicity. Researchers recently discovered that nHAP synthesized in vitro inhibits the growth of different types of tumor cells. Nanohydroxyapatite with potent drug adsorption and loading capacity has potential applications in tumor diagnosis and treatment. Because local tumors and areas of tumor metastasis also produce pathological nHAP in vivo to promote progression and invasion, the role of nHAP in tumorigenesis and development is perceived literature by many as Janus, the double‐faced deity in ancient Roman mythology. In the present review, two types of nHAP (those synthesized in vitro and those produced in vivo) that are affiliated with tumors, their mechanisms in tumor progression as well as their applications in tumor treatment are elucidated to create a backdrop for future research in this exciting, yet controversial arena.