A 62-year-old man with a 20-year history of sun exposure presents with a solitary, indurated, flesh-colored nodule on the dorsum of his hand. Dermoscopy reveals a central keratin plug surrounded by a collar of erythema and a 'starburst' pattern of radiating telangiectatic vessels. Histopathology shows a cup-shaped lesion with central keratin-filled crater, intact overlying epidermis, and surrounding chronic inflammation. Which of the following is the most likely diagnosis?