We then performed immunohistochemistry (IHC) of various tumor markers including mismatch repair (MMR) genes such as MutL homolog 1 (MLH1), MutS Homolog 2 (MSH2), MutS Homolog 6 (MSH6), and PMS1 Homolog 2 (PMS2) in order to confirm the correspondence of expressional patterns between PDOs and matched tumors. The gene discussed is MLH1; the disease is neoplasm.