CA9 and neoplasm: ELISA analysis confirmed that the sera of mice inoculated with B16-FL-CA IX contained 252 ± SD pg/ml of circulating CA IX, which roughly corresponds to the concentration found in human tumour patients.40–43 As expected, sera of mice inoculated with B16-NS-CA IX cells showed a diminished value of 28 ± SD pg/ml of CA IX, whereas sera of non-inoculated mice were CA IX-negative.