PCNA and tumor of salivary gland: In keeping with its potent mitogenic role in other target tissues [15–19, 25, 36, 37], RANKL drives significant salivary gland tumor cell proliferation (Fig 2A and 2B; S3 Fig) with expression levels of established biomarkers of cell division (i. e. cyclin D1 and proliferation cell nulear antigen (PCNA)) markedly elevated as compared to normal salivary gland tissue (Fig 2C).