CEACAM5 and neoplasm: When grafted subcutaneously, CO115-2C2 cells gave rise to circulating CEA levels that were directly related to the tumour volume (from 100 to 1000 ng ml−1 for tumours ranging from 100 to 1000 mm3), whereas no circulating CEA was detectable in CO115 and CO115-5F12 tumour-bearing mice.