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Cancer Stem Cells Can Go It Alone

At the heart of most cancers lies a very small number of abnormal cells known as cancer stem cells.

Unlike normal stem cells, cancer stem cell growth cannot be controlled. A goal of cancer researchers is to first identify molecular markers of these rare cells in order to find them and then devise strategies to kill them.

Nobel Laureate Renato Dulbecco, distinguished research professor and president emeritus of the Salk Institute, recently re-examined a cultured cell line he made in 1979 from a rat mammary adenocarcinoma. Three decades later, he finds that these cells exhibit many qualities of breast cancer stem cells.

This work, reported in Proceedings of the National Academy of Sciences, means that Dulbecco's breast cancer line, known as LA7, will likely provide researchers with a ready and abundant source of cancer stem cells for analysis through every step of tumor formation. It also supports the current hypothesis that an entire tumor can emerge from one aberrant stem cell.

Together with Ileana Zucchi, a molecular biologist at the Institute for Biological Technology in Milan, Italy, Dulbecco observed that cells from the line formed tumors after they were injected into normal breast tissue of female mice.

Injection of even one single cell from the cultured line gave rise to breast tumors in those mice.

Interestingly, like normal stem cells, LA7 cells prodded with appropriate cues can form cell types usually seen in the mammary gland, such as milk-producing alveoli and duct tissues. And, also like normal stem cells, these cells can divide or "self-renew."

However, cancer stem cells do not respond to environmental signals that would regulate the process of self-renewal in normal stem cells.

Confirmation that a tumor can arise from one unregulated cell is sobering: It means that successful and permanent removal of a tumor will require eradication of every potential cancer stem cell.

The good news is that Dulbecco and Zucchi's work should speed identification of early markers of these cells as well as suggest therapies to target these cells for destruction before they have time to give rise to a breast tumor.