Piecemeal degranulation in human tumour pheochromocytes.

Piecemeal degranulation (PMD) has been recognized in two cases of human pheochromocytoma from the adrenal medulla, which were studied by transmission electron microscopy. Tumour pheochromocytes presented a highly characteristic cytoplasmic admixture of normal resting granules, swollen granules with eroded matrices and enlarged empty containers. Chromaffin granules that appeared to be normal and altered granules maintained their individual structure, and did not fuse with each other or with the plasma membrane. In accordance with the currently accepted model for granule discharge during PMD, electron-dense or clear vesicles 30-150 nm in diameter were seen either attached to the surface of chromaffin granules and the plasma membrane or free in the cytosol. This is the first description of PMD in human adrenal chromaffin cells and, in addition, is the first report of PMD in tumour secretory cells. These findings add further to the concept that PMD may have a broader spectrum of expression than hitherto recognized.