Their findings, published in the December issue of Clinical Cancer Research and available online, show that one-third of the longtime disease-free patients in the study had circulating tumor cells (CTCs). The presence of CTCs is often associated with a higher risk of recurrence if they are found soon after a mastectomy. The UT Southwestern discovery that CTCs can be found in patients up to 20 years after mastectomy is notable because these patients have a very low risk of recurrence. After 20 years, the risk of recurrence rises to 20 percent of survivors, and scientists are still unsure why.
"Dormancy is a mysterious phenomenon that occurs in certain types of cancer," said Dr. Jonathan Uhr, lead author of the study and professor in the Cancer Immunobiology Center and of microbiology and internal medicine. "The term refers to a recurrence of cancer long after the tumor has been removed."
Based on his previous data gathered from mouse models of cancer dormancy, Dr. Uhr and colleagues used a stringent and sensitive set of tests to identify CTCs in women who had mastectomies and had been clinically cancer-free for at least seven years. The investigators collected blood from 36 study participants. Of those, 13 breast-cancer survivors had CTCs, but the number of CTCs was low and remained low. Because CTCs are short-lived, they must be constantly replenished, possibly from many tiny tumors somewhere in the body.
Dr. Uhr said that there appears to be a precise balance between tumor cell replication and cell death. Those who stay healthy may have developed a way of keeping the size of the tumor cell population in check, making breast cancer a chronic illness in these patients, he said.