This review highlights recent findings on the versatile serpin protein, pigment epithelium-derived factor (PEDF), in relation to cancer diagnosis, treatment and prognosis. PEDF was initially discovered in the eye but has since been reported to be relevant to various biological roles in the body, and when awry, to clinically lead to various disease states such as neoplasia. At the preclinical stage, potent effects have been reported in studies focussing on apoptosis, metastasis, oxidative stress, immune stimulation and metabolism. Apart from full-length proteins, short peptides based on PEDF have shown promise against cancer. For diagnosis and prognosis, PEDF levels in tumour specimens or in circulation have the potential to serve as biomarkers, most probably in combination with other biomarkers of cancer initiation and progression. Lastly, this review discusses the growing list of studies that point out the perceived pro-cancerous effects of PEDF, though this is clearly outweighed by the anticancer publications. Thus, this review provides a comprehensive and balanced listing of the oncological studies associated with this protein to date, drawing conclusions on whether this potent antiangiogenic protein and its peptides can be used in the future for better cancer treatment, especially against metastasis.