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Last Updated: Dec 27th, 2006 - 19:07:47 |
US study: Bone marrow cells help cancer spread
People often believe cancer spreads to another organ after tumor cells fall from the cancer site and move to the new organ to develop another tumor. A new US study, published in the current issue of Nature, says that cancer dispatches agents to another organ and makes a base before tumor cells travel to the target and start to grow into a secondary cancer.
By definition, metastasis (the spread of cancer from its primary site to other places in the body) includes these processes: cancer cells can break away from a primary tumor, penetrate into lymphatic and blood vessels, circulate through the bloodstream, and grow in a distant focus (metastasize) in normal tissues elsewhere in the body. The details are still unclear.
The current finding suggests that blocking the agents can prevent the spread of cancer or metastasis.
Dr. David Lyden of Cornell University in New York told Reuters they studied the first few steps involved in metastasis that had been previously unknown.
If the tumor is destined to inflict another organ, it somehow mobilizes normal bone marrow cells and sends them to a new site first in order to get the new site ready for the arrival of cancerous cells to colonize.
Growth factors released by the primary tumor trigger the production of an adhesive protein called fibronectin at the metastasis site. The protein attracts and traps the normal bone marrow cells to form a landing spot for the cancer cells to arrive and grow. Bone marrow cells start to move to the target when other growth factors give them a go signal.
If bone marrow cells cannot be used, and the landing site cannot be created, then cancer cells cannot land on the new organ and proliferate.
The agents determine which organ should be the next victim. The number of the moving bone marrow cells can be the measure to predict if a cancer is capable of spreading.
Once bone marrow cells form a base, tumor cells grow into a secondary cancer.
Studies of mice indicate the bone marrow cells can be stopped using antibodies. Researchers believe the blocking also works in humans against metastasis.
For the study, researchers irradiated mice to kill all their bone marrow cells. Without bone marrow cells, the cancerous cells cannot move.
Then bone marrow cells tagged with a green fluorescent protein marker were injected in the treated mice. The marker allows researchers to observe their movement under a microscope.
The mice were injected with lung or skin cancer cells with a red fluorescent protein attached for easier observation.
As a result, primary skin cancer was formed and then it spread to the lungs.
It was found that the tagged bone marrow cells moved to the lungs days before any tumor cells did. Tagged cancer cells also arrived at the same site as the bone marrow cells.
Some mice were injected with cancer cell culture rather than cancer cells. The research found the bone marrow cells also moved the lungs indicating that movement of bone marrow cells were affected by some factor released by cancer cells.
"For the first time we have shown the initial steps involved in metastasis," Dr Lyden told the BBC News Web site. "By blocking bone marrow cells using antibodies, we are capable of preventing tumor cells implanting and thus the spread of cancer."
It is believed that bone marrow cells aid the growth of secondary cancer by making a protein called vascular endothelial growth factor receptor 1 (VEGFR1), which boosts the formation of tumor blood vessels. When mice were given antibodies, there was no metastasis.
Some anticancer drugs such as Avastin from Genentech Inc. inhibit the growth of cancer blood vessels. However, these drugs block vascular endothelial growth factor, which works with VEGFR1 to help grow blood vessels that the new cancer cells need, according to the Boston Globe.
The finding could result in some positive implications. Clinical trials for an antibody treatment is expected within a year.
"Cancer, the second leading cause of death among Americans, is responsible for one of every four deaths in the United States. In 2005, more than 570,000 Americans or more than 1,500 people a day will die of cancer. Close to 1.4 million new cases will be diagnosed in 2005. This estimate does not include preinvasive cancer or the more than 1 million cases of nonmelanoma skin cancer expected to be diagnosed this year," according to the U.S. Centers for Disease Control and Prevention.
© 2004-2005 by foodconsumer.org unless otherwise specified
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