TUESDAY, April 11, 2006 (HealthDay News) -- The benefit of breast cancer chemotherapy may depend on the status of estrogen receptors lying on the surface of tumor cells, according to a new analysis of three clinical trials.
"Chemotherapy is helping [treat] estrogen receptor-negative tumors much more than estrogen receptor-positive," said study lead author Donald Berry, chairman of the department of biostatistics and applied mathematics at the University of Texas M.D. Anderson Cancer Center, in Houston.
That's been suspected for a long time, experts said, but this new analysis lends more credence to the theory.
Breast tumors are classified as either estrogen receptor-positive or negative, depending on cellular receptivity to the hormone. "An estrogen receptor-positive tumor has lot of receptors for estrogen, and estrogen is the fuel that drives the breast cancer," Berry explained. Typically, he said, women with cancers that have spread to nearby lymph nodes are given chemotherapy. Those with estrogen receptor-positive tumors are also prescribed tamoxifen, which inhibits estrogen uptake by cancer cells.
Berry's team analyzed data from three clinical trials conducted over the past 20 years with a total of 6,644 patients.
The researchers found that 22.8 percent more estrogen receptor (ER)-negative patients were disease-free after five years if they got chemotherapy, compared with 7 percent of the ER-positive patients.
Improvements in survival were 16.7 percent for patients with ER-negative tumors, versus 4 percent for ER-positive. Put another way, "one in six women with ER-negative are alive after five years because of the improvement in chemo," Berry said, whereas just "one in 25 women who are ER-positive are alive after five years because of the improvements."
Dr. Kent Osborne, director of the Cancer Center at the Baylor College of Medicine in Houston, called the new analysis good news. "This is a little bit stronger data than some of the earlier studies published a long time ago, which were sort of anecdotal series."
However, Osborne pointed out that, due to a lack of data, Berry's team "only looked at whether the tumor was ER-positive or ER-negative. There are degrees of being positive."
The new analysis should help women and their doctors make important treatment decisions, the experts said.
"There is a growing body of evidence, and this is one, that suggests the chemotherapy benefit to patients in those with estrogen receptor-positive is much less," Osborne said. "When patients are trying to decide whether to take chemotherapy or not, they need to be aware [that] yes, there may be a benefit, but it is likely to be very small if they are estrogen receptor-positive, particularly if they are strongly estrogen receptor-positive."
"It's a very clear decision to get more intensive chemotherapy for estrogen receptor-negative [tumors]," said Berry. "It is less clear for estrogen receptor-positive."
"About 60 to 65 percent of breast cancers are estrogen receptor-positive but it depends on age," Berry said. "The older the woman, the more likely she is to be ER-positive."
More information
For more on breast cancer, head to the American Cancer Society.
