In a cohort-based association study involving 111 cancer patients, genotyping of <i>ABCC1</i>/<i>MRP1</i>, <i>ABCC2</i>/<i>MRP2</i>, and <i>ABCC4</i>/<i>MRP4</i> was conducted using real-time PCR with TaqMan probes. The gene discussed is ABCC4; the disease is cancer.