Many tumor suppressor genes are located on chromosome 3p, including TP53, VHL, MLH1, TGFBR2, THRB, RARB, and FHIT. Loss of one copy of chromosome 3p is one of the most frequent and early events in human cancer, found in 96% of lung tumors and 78% of lung preneoplastic lesions (19). The gene discussed is MLH1; the disease is cancer.