A 58-year-old woman presents with a 3-month history of unilateral nipple itching and scaling. On examination, the feature marked **B** in the diagram—eczematous scaling of the nipple—is noted, along with recent nipple retraction. The lesion has not responded to topical corticosteroid therapy for 2 weeks. A full-thickness punch biopsy of the nipple-areolar complex is performed. Which of the following histopathological findings would most strongly support the diagnosis and explain the clinical presentation?