In breast cancer, a high number of CTCs (more than 5 cells in 7.5 ml of blood collected from the veins) indicates aggressive metastatic disease, or disease that has stopped responding to treatment. “If we can validate this approach for uveal melanoma, we hope to be able to catch cancer before it develops into metastatic disease,” says Takami Sato, M.D., the K. Hasumi Professor of Medical Oncology at Thomas Jefferson University and lead investigator on the paper. “The work by Dr. Mizue Terai and others at Jefferson gives us hope that CTC might be useful for uveal melanoma patients as well. On the other hand, our research raised a concern that venous blood specimencs, which are tested as the standard practice for CTC measurement, might not be the best source for CTC detection.” The results were published online in the journal EBioMedicine.
Circulating tumor cells are larger than other blood cells and have different chanracterisitics from normal blood cells. Therefore, CTCs can be detectable in the blood samples with modern technology. Most commonly, blood samples are obtained from a patient’s vein, which has already passed through an intricate sieve of narrow capillaries throughout the body before draining to the veins. Indeed, when Mizue Terai, PhD and colleagues compared blood samples taken from uveal melanoma patients’ veins compared to that collected from arteries, they saw a much higher number of circulating tumor cells in blood collected from the arteries than in the veins. In fact, all of the uveal melanoma patients with multiple liver metastasis had CTCs present in their arterial blood, while only 53 percent of blood sampled from the veins of those same patients had CTCs.
Although it is more technically difficult to collect blood from an artery than a vein, this and other research suggests that checking arterial blood may be a more accurate way of assessing circulating tumor number, and therefore metastatic disease.