Breast cancer's outside agitators
Cells surrounding the
ducts where cancer starts
are hardly innocent
bystanders
By Richard Saltus
Although they carry life-nourishing liquid to the mother's nipple and the infant's lips, the network of milk ducts inside the breast can also be a cancer hotspot. Most breast cancers originate as abnormal cells within these narrow channels. If the cells breach the ducts' walls and invade nearby tissues and blood vessels, they're likely to form a dangerous malignant tumor.
Nearly 216,000 U.S. women are expected to receive a diagnosis of breast cancer in 2005, with about 40,000 deaths according to the American Cancer Society (ACS). If scientists are to reduce this toll significantly, they'll have to learn more about how good genes and normal breast cells turn bad.
Breast cancer starts in the lining of milk ducts when cells grow uncontrollably and may break out to invade breast tissue. Kornelia Polyak, MD, PhD, and colleagues show that noncancerous "stromal" cells outside the ducts can send signals that make the cancer more aggressive.
(Illustration by John DiGianni)
The trouble begins when cells in the epithelium—the smooth layer of cells lining the milk ducts—lose control of their growth and over-reproduce. Unrestrained, the cells pile up in bunches, sometimes entirely filling the canals.
While the cancer cells remain confined harmlessly within the milk duct, as they often do for years or decades, the condition is called DCIS, or ductal carcinoma in situ. The ACS expects about 50,500 cases of DCIS to be diagnosed in 2005.
The major concern with DCIS is that it may become an invasive cancer.
Unpredictably, clusters of DCIS can stage a breakout. Gene mutations equip the cells with weapons for becoming mobile and boring through the basement membrane, a barrier between the ducts and surrounding cells. Having penetrated this barrier, the renegade cells can migrate into nearby tissues, enter blood vessels, and travel to other parts of the body.
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