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Researchers study spread of cancer to bone (6/1/98)

The bone is one of the most common places for aggressive breast and prostate cancer to spread, yet other types of cancer tend to leave this fertile area alone. Why?

"Perhaps breast and prostate cancer possess inherent capabilities which not only direct them to bone but also enable them to survive, proliferate and colonize in bone," said Toshiyuki Yoneda, DDS, PhD, professor of medicine in the division of endocrinology and metabolism at The University of Texas Health Science Center at San Antonio. "One important goal of research in this area is to identify these capabilities at the molecular level."

Complex cellular processes contribute to the progression of bone metastasis, Dr. Yoneda wrote in an article in the European Journal of Cancer, volume 34, number 2, published this year. Prostate and breast cancer distort normal regulation of bone cells, affecting "bone-building" cells as well as "bone-destroying cells."

The cells that form bone are known by researchers as osteoblasts, and the cells that break down bone are called osteoclasts. The work of these bone "masons" is continual and lifelong. In the adult skeleton, old bone is replaced by new bone within about 60 days. That's why a fracture generally can heal in that amount of time. In children, bone replaces bone even faster.

The builder osteoblasts produce and store growth factors in bone which may serve as essential nutrients for cancer cells - and these factors are released continually into the bone marrow cavity during bone remodeling. "Thus, bone provides a fertile micro-environment which facilitates colonization of metastatic cancer cells," Dr. Yoneda said. Metastatic cancer cells are those that have spread from the initial tumor to another part of the body.

After the lungs and the liver, bone is the third most common site for cancer to metastasize. More than 70 percent of women with breast cancer who suffer a recurrence will have some involvement of the bone, and in men with prostate cancer who suffer recurrence, 80 percent will have some bone involvement. In addition, once cancer has colonized bone it is extremely difficult to treat with currently available therapies.

Dr. Yoneda's lab and others are attempting to identify specific molecules that are involved in the steps of breast cancer metastasis to bone, as well as stimulatory factors in prostate cancer. This ongoing work is supported by several grants, including two five-year, $800,000 awards from the National Institutes of Health/National Cancer Institute.

Dr. Yoneda's Health Science Center colleagues include Gregory R. Mundy, MD, professor of medicine and chief of the endocrinology and metabolism division, and Theresa Guise, MD, associate professor of medicine.

Contact: Will Sansom (210) 567-2570