DHFR and plasma cell myeloma: The relative mRNA expression levels of four folate pathway genes (RFC, GGH, FPGS and DHFR) were examined in eight myeloma cell lines, including four resistant lines (ARP-1, CAG, RPMI 8228, U266) and four sensitive lines (ARH-77, KMS-11, MM.1s, PCNY-1B).