Acanthosis nigricans (AN) is a skin disorder characterized by focal or diffuse hyperkeratosis symmetric hyperpigmentation of the skin and oral cavity mucosa. Various neoplasms, especially gastrointestinal adenocarcinomas are associated with acanthosis nigricans (AN malignant). Chemotherapy may cause regression of skin lesions. The etiology of AN is not clear. A role of growth factors such as melanocyte stimulating hormone alpha, transforming growth factor alpha, and insulin-like growth factor 1 has been discussed. Two cases of AN have been reported in this paper. Both have been associated with gastric adenocarcinoma. In the first case skin lesions were sensitive to chemotherapy (until cancer progression), while in the second case treatment had to be discontinued because of cardiotoxity without regression of skin lesions.