IMMUNOCYTOCHEMICAL IDENTIFICATION OF OXYPHILIC MITOCHONDRION-RICH CELLS

Mitochondrion-rich oxyphilic cells and related tumors are recognizable morphologically. However, oxyphilic properties are unspecific because, in some instances, they are related to intra-cytoplasmic accumulation of organelles other than mitochondria, and the cytological typing does not correspond to the ultrastructural one. Moreover, the extent of oxyphilic transformation in some cases might not be so prominent, and the typical features of large granular eosinophilic cytoplasm might be missing. This is true especially in poorly differentiated oxyphilic tumors, as observed in some Hurthle cell carcinomas and in composite tumors in which the oxyphilic cell population is admired with other cell types (e.g., kidney and thyroid carcinomas). A commercially available monoclonal antibody (clone 113-1), which recognizes a mitochondrial antigen, was evaluated by immunohistochemistry in formalin-fixed, paraffin-embedded tissues with an oxyphilic cell component and in a series of oncocytic tumors. A working dilution of 1:100 was chosen for immunoperoxidase staining: this allowed marking of selectively mitochondrion-rich cells and tumors but not normal tissues, non-oxyphilic carcinomas, or tumors with oxyphilic properties unrelated to mitochondria. In some tumors, especially in thyroid and kidney neoplasms, oxyphilic appearance has been linked to a unique biological behavior. The marker here tested can be useful to reach more definite and reproducible criteria for the definition of mitochondrion-rich oxyphilic cells.