|here's another VEGF story. although VICL's patent would deliver it, i still think it's interesting to keep track of the connections.|
Tuesday May 8 5:52 PM ET
Hormone May Spur Tumor Blood Vessel Growth
By Merritt McKinney
NEW YORK (Reuters Health) - The hormone progesterone may contribute to breast cancer by boosting a blood vessel growth factor that helps tumors to grow, according to results of a preliminary study conducted on laboratory-grown cancer cells.
The hormone appears to stimulate production of VEGF, which is involved in the creation of blood vessels for normal cells and tumors--a process called angiogenesis.
The findings suggest one reason why medications that block progesterone may be useful for treating breast cancer. In the study, the researchers used the abortion drug RU-486--which is a progesterone-blocking agent--to halt the process in the laboratory. Progesterone is the hormone that prepares the uterus for egg implantation and pregnancy.
Estrogen has been shown to help regulate the expression of VEGF (or vascular endothelial growth factor) in breast cancer cells, but less is known about the effects of progesterone.
The results of the research are not surprising, according to Dr. Fairooz Kabbinavar, of the Jonsson Comprehensive Cancer Center at the University of California, Los Angeles.
The study is ``a small piece of the puzzle that tells you that cancer and malignant angiogenesis go hand-in-hand,'' he told Reuters Health in an interview. It helps ``unlock the mechanism'' of the creation of blood vessels to supply tumors, according to Kabbinavar, who was not involved in the study.
Although RU-486 has not been used to treat breast cancer, Kabbinavar said that other drugs that block progesterone are used to treat the disease.
Even though the study found a link between progesterone and the secretion of VEGF, Kabbinavar said the study ``should not increase the level of concern'' for women taking hormone replacement therapy that contains a progestin, a synthetic version of progesterone. He pointed out that the findings are based on laboratory experiments in a single type of breast cancer cell.
In the study, Dr. Salman M. Hyder and colleagues at the University of Texas Health Science Center-Houston exposed human breast cancer cells to progestins. Within a few hours of exposing the cells to progestins, the expression of VEGF increased two to five times, according to the report in the International Journal of Cancer.
The investigators achieved similar results when they tested a variety of naturally occurring and man-made progestins that are used in hormone replacement therapy and birth control pills.
But when the researchers added RU-486, which blocks the activity of progestins, the increased expression of VEGF stopped.
Since VEGF can increase the size of normal and cancerous tissues, progestin may accelerate the growth of some types of breast tumors, Hyder and colleagues report. This activity of progestins, the team points out, could be ``particularly insidious'' in women with undiagnosed tumors that were triggered by estrogen and then encouraged by progestins--either natural or pharmaceutical versions.
There is some concern that progestins may encourage the progression of some types of breast cancer, Hyder told Reuters Health in an interview. This study ``suggests that this may be the case,'' he said.
He noted that some research has indicated that the risk of breast cancer may be elevated in women taking estrogen in combination with a progestin but not in women taking estrogen alone. The current research may help explain the increased risk for women taking a progestin, according to Hyder.
But the Texas researcher cautioned that the apparent effects of progestins on VEGF need to be confirmed. ``It's too soon to conclude anything,'' he stated.
Hyder also noted that for women who still have an intact uterus, progestins are necessary to prevent uterine cancer in women taking estrogen replacement. And some studies have found that high doses of progestins can actually be beneficial for some breast cancer patients.
Much more study is needed to determine if the laboratory results actually translate into risks for healthy women, or those with breast cancer.
SOURCE: International Journal of Cancer 2001;92:469-473.