(ANNOUNCER OPEN):
What causes benign tumors to develop? Speaking at a presentation on cancer during the "2001 NIH Mini-Med School," Dr. Alan Rabson, Deputy Director of the National Cancer Institute, says tumors develop in two ways.

(RABSON):
"One way is cells can grow in an unrestricted way. So cell numbers increase. Now, what makes cell numbers increase? There are genes that cause proliferation by phosphorylating something that shouldn't be phosphorylated and activating it when it's not supposed to be activated. So they're called oncogenes, because they cause tumors. Now, the other thing we discovered later, which is even more exciting is, is that a cell is so regulated - there's all these genes that regulate growth - so the cell regulators that keep cells from dividing are called supressor genes. So you can get a mass of cells either if you're making too many or if you've lost a supressor gene which is supposed to keep cells from dividing."

(JACKSON CLOSE):
This is Calvin Jackson, the National Institutes of Health, Bethesda, Maryland.