Extensive DNA fragmentation in oxyphilic cell lesions of the thyroid

The in situ end-labeling (ISEL) method demonstrates DNA fragmentation, comm only regarded as a marker of apoptosis. We investigated by the ISEL procedu re a series of 52 thyroid lesions, including 24 lesions of mitochondrion-ri ch oxyphilic cells, both benign and malignant, and 28 non-oxyphilic control tumors. A high percentage of nuclear ISEL staining (approximating to 100% in most cases) was observed in the vast majority of oxyphilic cells from bo th adenomas and carcinomas, in the absence of morphological apoptotic chang es and with no immunocytochemical evidence of caspase activation. This patt ern of DNA fragmentation was not observed in non-oxyphilic lesions and was confirmed in total extracted DNA. Moreover, a peculiar cytoplasmic staining was also observed in oxyphilic cells from both benign and malignant lesion s, probably related to abnormal fragmentation of mitochondrial DNA. Similar staining patterns were detected in oxyphilic cell tumors of other organs ( parathyroids, salivary glands, and kidneys). These findings are consistent with an extensive DNA fragmentation peculiar to oxyphilic cells, which is n ot directly related to apoptosis and whose origin and biological significan ce are presently unknown.