THURSDAY, April 21 (HealthDay News) -- Two commonly used blood pressure medications seem to have opposite effects on the chances of breast cancer recurring in women with a personal history of the disease.

Preliminary findings show that ACE inhibitors increased the risk of recurrence, which surprised even the researchers, who published their study online in the journal Breast Cancer Research and Treatment.

On the other hand, beta blockers seemed to reduce the risk, which is in keeping with prior studies on the subject.

Fortunately, when the two drugs were combined, beta blockers seemed to mitigate the increased risk of recurrence linked with ACE inhibitors.

The study reflects the increasing interest among scientists in the effect the "microenvironment" -- which can include chronically used medications in addition to alcohol, tobacco and physical activity -- might have on the course of a particular woman's breast cancer.

"Tumors may be living in the breast before we even known about it. The microenvironment may either facilitate or keep under control whether the cells disseminate," said study first author Dr. Patricia A. Ganz, director of cancer prevention and control research at the Jonsson Comprehensive Cancer Center at University of California Los Angeles.

The study suggested that certain medications used to treat heart disease and high blood pressure might have an adverse effect on breast cancer survivors, she and the other researchers noted.

A 2010 study by Jonsson Comprehensive Cancer Center researchers on mice had already looked at beta blockers and cancer spread (or metastasis). That study began by documenting that stress can affect how fast and how widely a tumor spreads in rodents. The mice were confined in a small tube for a couple of hours a day, and the resulting stress prompted immune cells to gather in the tumor cells, enabling quicker metastasis and a 30-fold increase in cancer spread, deeper analysis revealed.

But in this animal model, beta blockers managed to block the signals that were recruiting the immune cells, explained Ganz.

That same year, a study of more than 400 women in England and Germany found that women on beta blockers also had a lower likelihood of breast cancer recurrence.

The UCLA researchers decided to delve deeper, working with other scientists on a database of 1,779 women with early-stage breast cancer who had been treated at a large health maintenance organization in northern California and followed for about eight years in a study called Life After Cancer Epidemiology (LACE).

The women in the group who were taking ACE inhibitors had a 56 percent increased risk of a recurrence, although they had no increased risk of death.

The 14 percent of women who were taking propanolol -- the beta blocker considered most likely to have a protective effect -- had a reduced risk of recurrence. Because the number of women in this group was so small, the findings did not reach statistical significance, Ganz said, although "it was going in the right direction in terms of being protective."

The risk associated with taking both drugs together was somewhat in the middle.

The study was funded by the Jonsson Comprehensive Cancer Center Foundation, the Breast Cancer Research Foundation and the U.S. National Cancer Institute.

Noting the need for further studies, Ganz is working with researchers in Denmark and Canada to evaluate the same medications and their relationship to recurrence in much larger samples of breast cancer patients.

"We've always been addressing the treatment of the cancer itself but in this study [they were looking at whether] there is something in the host, in the milieu that makes us more susceptible to the development of a malignancy. Is there something we can actually change?" said Dr. Lauren Cassell, chief of breast surgery at Lenox Hill Hospital in New York City.

Still, the research is very preliminary. "People have to realize this is just a work-in-progress and shouldn't stop their medicines if they happen to be on one of these medications," said Dr. Nieca Goldberg, director of the Women's Heart Program at NYU Langone Medical Center in New York City.

"If they are concerned because they have breast cancer or they're at high risk for breast cancer," Goldberg said, "they should really express this to their doctors because there are other options for medicines."

More information

The U.S. National Cancer Institute has more on breast cancer.