Necrolytic Migratory Erythema

A 58-year-old man presents with a 6-month history of progressive skin lesions characterized by migratory annular erosive erythema with central clearing and peripheral spread, predominantly affecting the intertriginous areas, perineum, and perioral region. The lesions follow a cyclical pattern of erythema, vesiculation, erosion, and crusting over 7–14 days. He also reports recent-onset mild diabetes mellitus and has been found to have a normochromic normocytic anemia. Imaging reveals a 3 cm mass in the pancreatic head. The structure marked **A** in the diagram represents the distinctive cutaneous manifestation seen in this patient. Which of the following is the most likely underlying diagnosis?