We initially selected candidates based on common use as RGs in breast cancer cell lines (e.g. CCSER2 in MCF-7, T-47D, MDA-MB-231 and MDA-MB-468 cell lines), or as stable RGs in other models of hypoxia (e.g. RPLP1 in hypoxic pre-conditioned human neural stem cells) [46–48], and further stratified candidates based on a calculated similarity score (s) which was used to determine the similarity of read counts in genes from breast cancer cell lines cultured in 20% or 1% O2. This evidence concerns the gene RPLP1 and breast carcinoma.