Atypical carcinoid tumor of the lung, associated with giant-cell transformation in bone metastasis

A case of neuroendocrine lung tumor located beneath the pleura in a 71-year-old woman is reported. At autopsy, the tumor was found to have metastasized to the bones and liver without involving the hilar lymph nodes. Histologically, the tumor cells at the primary site and in the liver metastasis exhibited a carcinoid-like organoid structure, whereas pleomorphic giant cells were noted in the bone metastasis. The argyrophilic tumor cells were immunoreactive for neuron-specific enolase, chromogranin A, serotonin, calcitonin, calcitonin gene-related peptide, gastrin-releasing peptide, neuropeptide Y, gastrin, pancreatic polypeptide, glicentin, the alpha-subunit of human chorionic gonadotropin, keratin, epithelial membrane antigen, Leu M1 and carcinoembryonic antigen. Electron microscopy revealed abundant neurosecretory granules in the cytoplasm. This was considered to be a rare case of neuroendocrine lung tumor showing carcinoid-like histology at the primary site and large-cell transformation in bone metastasis.