FRIDAY, March 10 (HealthDay News) -- An extract from dried papaya slows the growth of cancer cells in the laboratory, researchers report.

It's not clear if it will have the same effect on cancer in people, however.

University of Florida researcher Dr. Nam Dang and Japanese colleagues report that the papaya extract appears to affect the regulation of the body's immune system and doesn't cause side effects by harming normal cells.

The findings reflect the use of papaya by indigenous people in Australia and Vietnam, Dang, a professor of medicine, said in a news release from the university.

"Based on what I have seen and heard in a clinical setting, nobody who takes this extract experiences demonstrable toxicity; it seems like you could take it for a long time -- as long as it is effective," he said.

The researchers report that four strengths of papaya leaf extract slowed the growth of 10 types of cancer cell cultures, including cancers of the cervix, breast, liver, lung and pancreas.

The study was published in a recent issue of Journal of Ethnopharmacology.

More information

The U.S. National Cancer Institute has more on the various types of cancer.

WEDNESDAY, March 10 (HealthDay News) -- Though hormone therapy has proven useful in treating late-stage prostate cancer, it often results in the development of fatal secondary tumors that are resistant to such therapy.

Now, however, researchers working with mice believe they have uncovered a mechanism by which the secondary tumors gain their resistance -- a finding that eventually might help prolong the lives of men with prostate cancer.

Substances secreted during the body's inflammatory response to the hormone therapy appear to play a role in creating resistance to hormone therapy, according to the study, published in the March 11 issue of Nature.

Doctors might be able to delay the onset of hormone-resistant tumors by two to three years if subsequent research finds a way to control the effects of inflammation, according to the research team, which included scientists from the University of California, San Diego (UCSD), the Scripps Research Institute in Florida and the Engelhardt Institute of Molecular Biology in Moscow.

Hormone therapy for prostate cancer, also known as androgen deprivation therapy or androgen ablation therapy, involves the reduction of male hormones in the body, according to the American Cancer Society. These male hormones, called androgens, promote the growth of prostate cancer cells. Reducing androgen levels can cause prostate tumors to shrink or can retard their growth, making them easier to remove surgically or treat with radiation.

"That therapy usually works, but in too many patients it leads to the appearance of castration-resistant cancer -- cancer that no longer responds to androgen ablation therapy," said Michael Karin, one of the UCSD researchers. "That form of prostate cancer is more aggressive, more metastatic and more difficult to treat with traditional chemotherapy and radiation therapy."

By studying prostate cancer in mice, the researchers figured out that, as the prostate tumor shrinks, the dying cancer cells apparently send off signals that activate the body's immune response.

"What we think is going on is, when you kill the tumor, the body doesn't know it's the tumor being killed," Karin said. "It responds to it like there is tissue injury, a wound or something like that."

White blood cells called B-cells infiltrate the tumor and release a substance called lymphotoxin, a protein that kills infected cells. The research team found that exposure to lymphotoxin promoted the development of cancer cells resistant to hormone therapy. Interfering with the inflammatory response delayed the development of castration-resistant cancer.

"It's somewhat counterintuitive, that the death of these androgen-resistant cells somehow contributes to androgen resistance," said Dr. Durado Brooks, director of prostate and colorectal cancer for the American Cancer Society.

The finding could be key in developing a means to delay or stop the development of therapy-resistant secondary tumors. Until now, research into this resistance has focused on the role that the cells' androgen receptors play in the process. But researchers now can also consider controlling inflammation as another way to delay resistance.

Don't expect anything useful for humans anytime soon. Researchers will have to first make sure that human prostate cancer responds in the same way that the cancer did in mice.

"There's going to have to be a lot more work done to clarify that the mechanisms in humans are the same as those they have identified in mouse prostate cancer," Brooks said. "It's going to be quite a while before this mouse model moves to the bedside and actual clinical practice, if it ever does."

But if the findings do transfer to humans, this new understanding of the role of inflammation in prostate cancer treatment could help extend lives.

"Androgen resistance is often one of the complications that occurs in later stages of prostate cancer management that often precedes death related to prostate cancer," Brooks said. "If there was a way to prolong the time between treatment and development of androgen resistance, we could prolong a man's life."

More information

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

TUESDAY, March 9 (HealthDay News) -- People with a particular genetic trait are at much higher risk of developing lung cancer from exposure to secondhand smoke than others, even if they rarely come into contact with it, a new study finds.

Researchers also found that smokers with this variant are more susceptible to lung cancer, whether they light up a lot or a little.

"If you carried the inherited risk and then you smoked, it didn't matter if you were a light smoker or a heavy smoker -- you were significantly more likely to develop lung cancer," study co-investigator Susan Pinney, an associate professor in the department of environmental health at the University of Cincinnati, said in a news release from the school.

About 200,000 people were diagnosed with lung cancer in 2005, according to the U.S. Centers for Disease Control and Prevention, and it kills more people than any other form of cancer.

The study authors examined nonsmokers, light smokers, moderate smokers and heavy smokers.

They found that family members who had the genetic trait were at higher risk of getting lung cancer even if they were light smokers. For them, moderate and heavy smoking didn't boost their risk very much.

By contrast, heavy smokers normally face a much higher risk of lung cancer than moderate smokers.

The study, conducted by the Genetic Epidemiology of Lung Cancer Consortium, was published online March 9 in advance of print publication March 15 in the journal Cancer Research.

More information

The National Cancer Institute has information on lung cancer.

FRIDAY, March 5 (HealthDay News) -- Freezing breast tumors helped stop the spread of the cancer in mice, a new study has found.

Researchers tested two cryoablation (freezing) techniques in mice with breast cancer. Both involve applying a cold probe to the tumor, but one method involves rapid freezing (about 30 seconds) of the tumor, while the other takes a few minutes. The mice that received cryoablation were compared to mice in which breast tumors were removed with surgery.

Both cryoablation methods killed breast tumors. Mice treated with the rapid cryoablation had fewer tumors spread to the lungs and had better survival than mice treated with the slower freezing technique or those treated with surgery alone, according to the researchers from the University of Michigan Comprehensive Cancer Center.

The better results associated with rapid cryoablation may result from changes in the immune system that help kill tumors. The slower freezing method didn't have the same effect on the immune system, the study authors found.

The study findings are published online in the journal Annals of Surgical Oncology.

The researchers are currently conducting a clinical trial to test the effectiveness of rapid cryoablation in breast cancer patients.

"Cryoablation has strong potential as a treatment for breast cancer," study lead author Dr. Michael Sabel, an associate professor of surgery at the University of Michigan Medical School, said in a news release. "Not only does it appear effective in treating the primary tumor with little cosmetic concerns, but it also may stimulate an immune response capable of eradicating any cells that have traveled throughout the body, reducing both local and distant recurrence, similar to giving a breast cancer vaccine," he explained.

"What we learned in this study is that all cryoablation is not equal," Sabel said. "The technique used to freeze the tissue can have a significant impact on how the immune system responds. The system we use today appears to be ideal for both destroying the tumor within the breast and generating an anti-cancer immune response."

Currently, cryoablation is used routinely to treat prostate cancer, kidney cancer and a number of cancers that have spread to the liver and bones.

More information

The U.S. National Cancer Institute has more about cryoablation as a cancer treatment.