ALDH9A1 and neoplasm: While HBB is by far the most abundant transcript differentially expressed between CTCs and primary tumours, we identified 16 other antioxidant genes as being significantly upregulated, including the ALDH family members ALDH9A1 and ALDH18A1, as well as SOD1 and PRDX family members (Fig. 5c; Supplementary Table 2).