They can be caused also by a plugged duct or by skin blocking a milk duct.

也可能是由于出乳口堵塞或者输乳管被皮肤堵塞。

youdao

In DCIS, abnormal cells multiply and form a growth within a breast milk duct .

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The cancer is noninvasive, which means it originally doesn't spread out of the milk duct to other parts of the breast.

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Even in the precancerous stage, called ductal carcinoma in situ (DCIS) when abnormal cells are confined to a milk duct, physicians almost always advise women to have a lumpectomy or mastectomy along with radiation, because about 20% of the 65, 000 cases of DCIS found every year in the U.S. become invasive cancer.

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