This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Skin tumors, Subject name: Dental
True about acanthosis nigricans 
Select and explain. 
A. Seen in axilla, B. It is associated with insulin resistance, C. It signifies internal malignancy, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: ACANTHOSIS NIGRICANS Classification * Hereditary AN * HAIR-AN syndrome:  Several endocrine disorders associated. HyperAndrogenism, Insulin Resistance and Acanthosis Nigricans. * Benign acquired AN:  Obesity associated. Earlier called pseudo AN. * Drug-induced AN:  Nicotinic acid, stilbestrol, coicosteroids, oral contraceptives. * Malignant AN:  Adenocarcinoma of stomach and genitourinary tract. Clinical Features Morphology:- Begins as hyperpigmentation and area appears  diy. Gradually, skin thickens and becomes velvety.  Surface of skin appears rugose and mammillated. The edge of lesion feathered. Sites of predilection:- Neck, axillae, and groins frequently. Other flexures (antecubital and popliteal fossae, face sometimes; submammary folds, wrists less frequently. Associations:- Depends on type of AN: * HAIR- AN syndrome: Several endocrine disorders associated. Insulin-resistant diabetes mellitus, hyperandrogenic states, Cushing's syndrome * Benign acquired AN: Skin tags in the major flexures. * Malignant AN:  Several associations: Tripe palms, Mucosal involvement, Severe itching. Investigations Rule out:- Underlying endocrinopathies. Underlying malignancies. Treatment:- Retinoic acid (0.025%) topically, response often  unsatisfactory. Ref:- Neena khanna; pg num:- 37,38