Lung, breast, prostate and colon carcinomas are the most frequent forms of malignancies. These tumors all arise from simple epithelial cells and express the intermediate filament protein cytokeratin 18 (CK18, keratin 18 or K18). During apoptosis, CK18 is cleaved by caspases at two sites. Macrophages recognize and engulph apoptotic cells. This does not necessarily occur in tumor tissue and caspase-cleaved CK18 may therefore be released to the extracellular environment and into the blood. Apoptosis of other cell types such as lymphoid cells will not generate CK18 cleavage products. Caspase-cleaved CK18 is therefore an ideal biomarker for measuring apoptosis of carcinoma cells using blood samples in research. Read more….