MTHFD1 and neoplasm: Likewise, silencing of the two SGOC network genes, PSAT1 and MTHFD1, that appeared transcriptionally upregulated in CDK12-KI/PyMT vs. WT/PyMT tumor cells (Fig. 6a), or silencing of CDK12, selectively inhibited the in vitro proliferation of CDK12-KI/PyMT tumor cells, with no effects on WT/PyMT cells (Fig. 6b, c).