A recent report involving 253 MBC patients showed that elevated CAIX soluble protein level (also evaluated using ELISA) along with the presence of ≥ 5 circulating tumor cells in 7.5 ml blood predicted shorter OS and shorter PFS; however, not all involved patients were treatment-naïve (Banys-Paluchowski et al., 2018). This evidence concerns the gene CA9 and neoplasm.