Circulating tumor cells are cells that break off from a cancer tumor and move into the blood stream. Doctors sometimes test for circulating tumor cells to see if breast cancer cells are active in areas of the body beyond the breast. The number of circulating tumor cells also affects a cancer's prognosis. Right now, finding 5 or more circulating breast cancer tumor cells in 7.5 milliliters (ml) of blood suggests a worse prognosis, and finding fewer than 5 circulating tumor cells suggests a better prognosis.
A study used a mathematical model to analyze how higher levels of circulating tumor cells affected the prognosis of people diagnosed with breast cancer. The model suggests that the more circulating tumor cells in the blood sample, the greater the person's risk of dying from breast cancer. Some day, doctors may be able to better estimate a person's prognosis based on the specific number of circulating breast cancer tumor cells rather than looking at only whether there are more or less than 5 cells in a blood sample.
The link between higher numbers of circulating tumor cells and worse prognosis was found in various types of breast cancer:
- hormone-receptor-positive cancer
- hormone-receptor-negative cancer
- HER2-positive cancer
- HER2-negative cancer
Still, the link between circulating tumor cells and prognosis was stronger in breast cancers with certain characteristics. The link was the strongest in estrogen-receptor-positive, HER2-positive breast cancers. The link was the weakest in triple-negative breast cancers (estrogen-receptor-negative, progesterone-receptor-negative, and HER2-negative).
While these results are interesting, more research is needed before doctors use specific numbers of circulating breast cancer tumor cells to help make treatment decisions.
Stay tuned to Breastcancer.org's Research News to learn more about lab research that may lead to better ways to diagnose and treat breast cancer.