To better understand the potential of PARPi, we present a comprehensive review of PARP-1 biology—the nuclear and extracellular functions of PARP-1; the impact of PARP-1 in cancer progression, with particular attention to the tumor microenvironment and distant metastasis; the preclinical efficacy of PARPi in impeding metastasis; and finally, the clinical advancements of PARPi in the early-cancer and metastatic contexts. This evidence concerns the gene PARP1 and neoplasm.