RPS21 and neoplasm: The other ribosomal protein gene transcripts identified in mouse mammary gland to correlate [15] with ZFAS1, i.e. RPS21, RPS24, RPL22 and RPL28, showed significant expression differences between normal and tumour samples (*P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001; Additional file 3: Figure S3D, F, H and J).