Carcinoid tumor of the lung with massive ossification: report of a case showing the evidence of osteomimicry and review of the literature.

Carcinoid tumor is one of the commonly encountered primary pulmonary neoplasms. Although it has been known to be accompanied by calcification and/or ossification, presentation with a large ossified mass is rare. We describe here the case of a 29-year-old female with the radiological finding of a single bony nodular lesion. Pathological examination of the surgically resected specimen led to the diagnosis of carcinoid tumor of the lung with massive ossification. Although histological features showed the tumor of low grade malignancy, subcarinal and right hilar lymph nodes were found to be positive for metastasis. Further immunohistochemical analysis revealed that the tumor cells expressed the osteogenic inducer protein, bone morphogenic protrein-2 [BMP-2] and osteoblastic marker protein, osteocalcin. We interpreted this to mean that the carcinoid tumor cells had acquired an osteoblastic phenotype and had subsequently developed marked intratumoral ossification. The relevant literature is reviewed and possible mechanisms of tumor-related osteogenesis are discussed.