This is the microscopic pattern of a small cell anaplastic (oat cell) carcinoma in which small dark blue cells with minimal cytoplasm are packed together in sheets. Oat cell carcinomas, which are a highly malignant form of neuroendocrine tumor, are often associated with paraneoplastic syndromes from hormonal effects. The ectopic ACTH syndrome and the syndrome of inappropriate ADH are two such syndromes.

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