Protein phosphatase 2A (PP2A) is a major serine/threonine phosphatase considered a potent tumor suppressor that critically regulates diverse cellular processes, including cell cycle progression, apoptosis, or DNA repair. PP2A is typically downregulated in cancers but mechanisms for its inactivation in human cancers are poorly understood. PP2A represents a family of more than 60 phosphatases. According to cellular context, each heterotrimeric PP2A holoenzyme exerts a unique role in cancer, and PP2A isoforms can act either as tumor suppressors or as promoters. Due to wide structural diversity, PP2A has been considered undruggable. However, increasing knowledge predisposes PP2A diversity to therapeutical targeting for the treatment of a broad range of cancer pathologies, including drug resistance or cloaking immune surveillance. In this review, we discuss the regulatory role of PP2A in cancer, its regulation by microRNA and hypoxia, its contribution to therapy resistance development, and the therapeutic potential of direct and indirect targeting, or combinatory administration with other anti-cancer drugs to improve cancer treatment outcomes.