Restoration of CEACAM1 expression in tumor cell lines often abolishes their oncogenicity in vivo as indicated by studies in syngeneic or immune-deficient mice, where reinsertion of various CEACAM1 isoforms in colorectal or prostate CEACAM1-negative tumor cells proved CEACAM1-L expression to be essential for maintaining a normal phenotype with the inhibition of allograft or xenograft tumor development [27, 28]. This evidence concerns the gene CEACAM1 and neoplasm.