CEACAM6 and cancer: In addition to the expression of CEACAM1 in contact-inhibited A549 cells, significant amounts of soluble variants of CEACAM5 and CEACAM6 were released by confluent A549 cells, thus exhibiting a likely source for increased CEACAM5 and CEACAM6 serum levels, which are frequently detected in cancer patients[31]–[33].