CEACAM1 and neoplasm: Importantly, in contrast to previously held notion that the long cytoplasmic domain isoform of CEACAM1 possesses tumor suppressive properties, we recently showed that forced expression of CEACAM1-S revert the malignant mammary epithelial cell line MCF7, which expresses low levels of CEACAM1-L, to a normal acinar morphology [29].