Constitutive activation of STAT3 correlates with cell proliferation in non-small-cell lung cancer (Alvarez et al., 2006) and pancreatic cancer (Sahu and Srivastava, 2009); conversely, inhibiting JAK2/STAT3 signaling arrests the growth of primary human cancer cells (Chiarle et al., 2005) and induces colorectal cancer cell apoptosis by modulating the Bcl-2 gene family, promoting the loss of mitochondrial transmembrane potential and increasing the levels of reactive oxygen species (Du et al., 2012). The gene discussed is JAK2; the disease is cancer.