Can Breast Cancer Surgery Nurture New Tumors?
Controversial Theory: Tumor Removal Unleashes Cancer Growth Factors in Younger Women
Sept. 13, 2005 -- Can removing a breast cancer cause rapid growth of tumors elsewhere in the body?
Yes, according to indirect evidence from a new analysis of clinical trial data. The controversial theory comes from Michael Retsky, PhD, of Children's Hospital/Harvard Medical School in Boston, and colleagues.
"We say this is indirect evidence; we think this is a key to understanding the biology of breast cancer," Retsky tells WebMD. "We certainly do not suggest any changes in clinical practice based on this. We hope this will entice clinical and experimental people to test these hypotheses."
However, the theory is extremely controversial. A spokesman for the American Cancer Society says the findings are based on a misreading of existing data.
Big Tumors Fighting Little Tumors
Retsky and colleagues looked at long-term data on breast cancer patients treated in Italy. They saw two peaks in breast cancer relapse among premenopausal women whose cancer had spread to their lymph nodes. One relapse peak came very early -- just 18 months after cancer diagnosis. The other started nearly five years after diagnosis.
This led them to a hypothesis. Cancers that relapse five or more years after cancer surgery, they suggest, come from single cancer cells in the body that grow slowly over time. Early relapses, they suggest, come from tiny, dormant cancers about 1 millimeter in size.
What makes these tiny cancers grow?
Animal studies show that big tumors give off chemical signals that keep smaller cancers from growing. When these big tumors are removed, the smaller cancers quickly grow blood vessels and become deadly.
The same thing may happen in some women after breast cancer surgery, Retsky says. And it's seen only in younger women, he suggests, because reproductive hormones boost the cancer-enhancing effect.
Breast Cancer Screening Paradox
For more evidence, Retsky's team looked at what some call the breast cancer screening paradox. It comes from observations in clinical trials comparing regular mammogram screening with no screening. In the first few years, women in their 40s who have mammograms -- but not those in their 50s -- have a higher risk of death than those not offered screening.
Over time, breast cancer screening shows a benefit for all women. But why the early increase in risk? Could it be due to women with node-positive breast cancer who suffer early relapses after surgery? Retsky suggests that it is.
Looking at data from studies of breast cancer screening, Retsky and colleagues saw about one excess death per 10,000 screened young women in the third year of screening. That, he says, is just what one would expect if his hypothesis is correct.
"It looked like surgery accelerated the disease by two years on average, which is the usual dormancy of this [blood vessel-free] tumor state," Retsky says. "All the data show this."