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Acanthosis nigricans presented as a greyish-brownish thickened patch in the back of the neck. It may also be manifested in other flexural areas of the body. The least harmful aetiological factor is excessive weight, especially in combination with polycystic ovarian syndrome (PCO) or insulin resistance, in which case dieting is often helpful. Detection of some other underlying endocrinological disturbance or (gastrointestinal) cancer is rarer.