Definition of Acanthosis nigricans

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Acanthosis nigricans: A skin condition characterized by dark, thickened, velvety patches, especially in the folds of skin in the armpit, groin, and back of the neck. It can occur with endocrine diseases such as Cushing disease and diabetes mellitus, from tumors of the pituitary gland, underlying malignancies, certain drugs, and as a genetic disorder. It is most common in people who have insulin resistance'those whose body is not responding correctly to the insulin that they make in their pancreas.