This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Skin
A 43 year old female presented with pigmentation on neck, axilla and other flexures. She is diabetic for few years and not under control. She is worried about the chance of skin cancer. All of the following are premalignant conditions, EXCEPT: 
Select and explain. 
A. Solar keratosis, B. Acanthosis nigricans, C. Bowen's disease, D. Porokeratosis
B: Acanthosis nigricans
Answer: B: Acanthosis nigricans 
Explanation: Acanthosis nigricans is probably the most readily recognized skin manifestation of diabetes and most cases are linked to obesity and insulin resistance. True association is rare between acanthosis nigricans and malignancy. It presents as brown to gray-black papillomatous cutaneous thickening in the flexural areas, including the posterolateral neck, axillae, groin, and abdominal folds. Ref: Kalus A.A., Chien A.J., Olerud J.E. (2012). Chapter 151. Diabetes Mellitus and Other Endocrine Diseases. In L.A. Goldsmith, S.I. Katz, B.A. Gilchrest, A.S. Paller, D.J. Leffell, N.A. Dallas (Eds), Fitzpatrick's Dermatology in General Medicine, 8e.