Cancer cells have distinct metabolism that highly depends on glycolysis instead of mitochondrial oxidative phosphorylation alone, known as aerobic glycolysis. Pyruvate kinase (PK), which catalyzes the final step of glycolysis, has emerged as a potential regulator of this metabolic phenotype. Expression of PK type M2 (PKM2) is increased and facilitates lactate production in cancer cells, which determines whether the glucose carbons are degraded to pyruvate and lactate or are channeled into synthetic processes. Modulation of PKM2 catalytic activity also regulates the synthesis of DNA and lipids that are required for cell proliferation. However, the mechanisms by which PKM2 coordinates high-energy requirements with high anabolic activities to support cancer cell proliferation are still not completely understood. This review summarizes the biological characteristics of PKM2 and discusses the dual role in cancer metabolism as well as the potential therapeutic applications. Given its pleiotropic effects on cancer biology, PKM2 represents an attractive target for cancer therapy.