DHFR and ovarian cancer: Researchers have demonstrated that oncogenes PIK3CA, MCL1, MYCN, DHFR, and eIF-5A2 were over-amplified via eccDNA in primary ovarian cancers, ovarian cancer cell line UACC-1598 and cervical cancer cell line HeLa, respectively (Radloff et al., 1967; McGill et al., 1993; Guan et al., 2001; Sun et al., 2015).