ABSTRACT
The detection of circulating tumor cells (CTC) has interested physicians since the 19th century, when Ashworth described a case of cancer in which cells similar to those in the tumor were found in the blood after death.1 However, the detection of CTC first gained widespread attention in 1955 when Engell reported the detection of CTC in
patients with various types of carcinomas using a cell block technique.2 Subsequently, between 1955 and 1965, several thousand patients with cancer (most with solid malignancies) were tested for CTC by 40 investigative teams using 20 different cytologic methods.3 These early studies reported very high positivity rates of CTC among patients with cancer (up to 100%).3 However, these results were soon shown to be due to false positives since circulating hematopoietic elements, especially megakaryocytes, were often confused with tumor cells. When cell preservation techniques were improved, allowing a better morphological analysis, the detection of true CTC by light microscopy was shown to have a very low sensitivity (approximately1%) in patients with cancer.3
