Immunoreactive somatostatin and calcitonin in pulmonary neuroendocrine tumor

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Abstract
A well‐differentiated neuroendocrine carcinoma of the lung that secreted immunoreactive somatostatin (IR‐SRIF) and IR‐calcitonin (CT) in a 72‐year‐old woman is described. The plasma concentrations of IR‐SRIF (57.5 pg/ml) and IR‐CT (340 pg/ml) before operation were significantly higher than the respective normal ranges. After resection of the tumor, the plasma CT level (105 pg/ml) decreased to within the normal range, and the SRIF level (32.7 pg/ml) also decreased, but was still abnormally higher, which suggested the presence of an unidentified remnant of the tumor. Abnormal accumulation of technetium 99m (99mTc) in the lumbar vertebrae was found 6 months after the operation, which indicated a metastatic tumor. The tissue concentrations of IR‐SRIF and IR‐CT were 103 and 94 ng/g wet weight, respectively, and SRIF‐IR tumor cells and CT‐IR tumor cells were demonstrated immunohistochemically. On gel‐filtration chromatography of the tumor tissue, two peaks of SRIF immunoreactivity were eluted in the positions of synthetic SRIF‐28 and SRIF‐14, respectively. Conversion of SRIF‐28 to SRIF‐14 was suggested from results on changes in the two IR‐SRIF components during incubation with a crude enzyme preparation extracted from the tumor tissue.