Micrometastasis in colorectal cancer

Colorectal cancer is one of the most common malignancies in the word and can be usually cured if diagnosed at an early stage. In the European area the estimated number of new cases of cancer in 1995 were approximately 334.000 and 189.000 died of cancer in that year. Despite recent progress in early detection and surgical therapy, the mortality remained unchanged over the past decades. The major reason for this disturbing discrepancy is that occult dissemination of viable cancer cells can occur at any stage of tumorigenesis. Occult dissemination of the tumor cells in patients with operable cancer may be considered a determinant of subsequent metastasis formation. Several groups have therefore designed immunocytochemical and molecular assays to identify such minimal amounts of residual tumor cells that have successfully invaded secondary organs. The question whether circulating tumor cells represent metastatic dissemination or are merely cancer cells without metastatic potential that have detached from the primary tumor, has been debated for over half a century.