Stem cells may have role in cancer relapses | Asbury Park Press Online

"In recent years, doctors have found stem cells in the liver, brain and other organs. Scientists believe these cells serve as reserve troops that help repair injuries, dividing into whatever type of tissue is needed, Jones says.
Cancer stem cells apparently pervert this process. Instead of creating new tissue to heal a wound, they create and replenish malignant tumors, Jones says.
Simeone sorted human pancreatic cancer cells according to protein markers that appear on their surface. In her research on pancreatic tumors, Simeone focused on cells with three particular proteins because those markers were found on cancer stem cells in earlier studies of cancer in different organs. Researchers injected the cells into mice, then waited to see which ones generated tumors.
As suspected, cancer cells with all three protein markers were the most aggressive. Mice developed tumors after being injected with as few as 100 of them. That's not many cells, Simeone says, considering that there are 'billions and billions' of cells in a human body."