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Nipple-sparing mastectomy

A procedure used to treat breast cancer in which the breast tissue is removed while the skin over the breast and the nipple are spared; an option used only when the breast tissue beneath the nipple and areola are free of cancer cells.

Nitric oxide

A colorless toxic gas formed by the oxidation of nitrogen; often used in medications to treat erectile dysfunction and other conditions because of its chemical signaling functions.


Excessive nighttime urination.

Non-obstructive coronary artery disease

A heart disease in which a coronary artery is obstructed by less than 50 percent.

Non-scalpel vasectomy

A minimally invasive vasectomy in which a surgeon cuts and seals the tubes that transport sperm cells during ejaculation without making an incision.

Non-seminoma tumor

A type of cancer that begins in cells that form sperm or eggs.