C-reactive protein (CRP) is an annular, homopentameric protein found in blood serum and plasma. It is an acute-phase protein of hepatic origin whose levels rise in response to tissue injury, infection or other inflammatory stimuli. After a single stimulus, CRP concentrations rise within 2 hours, peaking at 48 hours. With a constant half-life of 19 hours, CRP concentrations are solely determined by the rate of production and hence the severity of the precipitating cause. The physiological function of CRP is to bind to phosphocholine expressed on cells undergoing apoptosis. Upon binding to the damaged plasma membranes of dying cells, CRP activates the complement system via the C1q complex. As a sensitive inflammation marker, high CRP concentrations at baseline have been associated with early death after a cancer diagnosis. Additionally, elevated CRP levels are associated with increased risk of cancer of any type, along with many other diseases such as cardiovascular disease, diabetes, and rheumatoid arthritis.