IMMUNOELECTRON MICROSCOPY FOR CHROMOGRANIN-A IN SMALL-CELL NEUROENDOCRINE CARCINOMA OF LUNG

To see if immunoelectron microscopy can improve localization of neuros ecretory granules, postembedding immunolabelling for chromogranin A wa s performed on 15 examples of small cell anaplastic (neuroendocrine) c arcinomas primary in lung, five cases of bronchopulmonary carcinoids, and two cases of pheochromcytomas both the carcinoids and pheochromocy tomas had neurosecretory granule-rich cytoplasm by routine electron mi croscopy and some neurosecretory granules were identified in each of t he small cell carcinomas. Immunolabeling for chromogranin A resulted i n many colloidal gold particles over cytoplasmic secretory granules in both pheochromcytomas and four of the carcinoids. One carcinoid that was focally positive by immunoperoxidase staining was negative by immu noelectron microscopy. None of the 15 cases of small cell carcinoma st ained for chromogranin A using immunoperoxidase techniques, but three had a small number of secretory granules weakly labeled by the anti-ch romogranin A/colloidal gold complex. Immunoelectron microscopy, at lea st using standard glutaraldehyde fixation and epoxy resin embedding, d oes not increase the sensitivity of neurosecretory granule identificat ion in small cell neuroendocrine carcinomas of the lung. Results of ot her studies of this neoplasm suggest that despite transcription of chr omogranin genes, synthesis of the specific protein may occur to a limi ted extent or not at all.