Circulating tumour cells (CTCs) are rare tumor cells that have been investigated for diagnostic, prognosis and predictive biomarkers for different types of cancer. CTCs have been described back in 1869. They are not used in clinical practice at the moment, however CTCs were explored in breast, lung, prostate and colorectal cancers.
How rare are CTCs?
There is approximately 1 circulating tumor cell per ml of blood released by primary tumors or metastases that can be detected in peripheral blood.
What types of circulating tumor cells exist in clinical practice?
- Treatment based on CTCs used as liquid biopsy: Biopsies are invasive, expensive, time-consuming and potential harmful so using CTCs is one way of avoiding this procedure.
- Treatment based on CTC count or CTC variations: This depends on technique used and volume of blood screened.
- Treatment based on CTC biomarker expression: Isolating single cell of CTCs could be challenging.
What are the challenges of using circulating tumor cells in cancer screening?
Usage of Cellsearch technique in early non-metastatic cancer have shown low CTC detection rates (5-30% depending on the cancer type). This method is limited to some circulating epithelial cells so it cannot be used wildly. Unfortunately other techniques have not shown better detection rates.
How could CTCs be used as prognostic value?
Analysis of 1944 patients with breast cancer using CellSearch has shown that patients with increased CTCs have poor prognosis and decreased progression-free survival. Also evaluating CTCs count at baseline allows better prognosis of survival. Similar results are observed in patients with metastatic colon cancer, castration-resistant prostate cancer and small cell and non-small cell lung cancer.
CTCs value as prognostic factor was also observed in non-metastatic cancers with similar correlation – the higher amount of CTCs means poor prognosis.
How could CTCs be used in monitoring treatment response?
Studies with patients with metastatic breast cancer have shown that women with high baseline CTC counts, which is reduced after one cycle of chemotherapy have better prognosis than patients where their CTC count is elevated.
While CTCs have great potential as prognostic factor and in monitoring therapy, there are still lots of challenges before their implementation in clinical practise with biggest among them – discovering new methods and techniques for detection of CTCs.
Author: Olga Peycheva
Olga is a clinical research professional who has been working in clinical research since 2005. She has extensive experience in clinical research in Eastern and Western Europe.
Originally published on 2 July 2018