ESR1 and cancer: Among the enzymes that catalyze the activation of E1 to E2 (Figure 1), the mRNA levels of HSD17B1 were low (Smuc et al., 2006; Lépine et al., 2010; Cornel et al., 2012), decreased (Smuc and Rizner, 2009; Lépine et al., 2010), or increased in ERα-positive G1 cancers (Cornel et al., 2012).