ANTIMITOCHONDRIAL ANTIBODY-(113-1) IN THE DIFFERENTIAL-DIAGNOSIS OF GRANULAR RENAL-CELL TUMORS

Abundant granular eosinophilic cytoplasm is a common feature of renal oncocytoma, chromophobe renal cell carcinoma, eosinophilic variant of papillary renal cell carcinoma, and the granular variant of clear cell renal cell carcinoma (RCC). Each of these entities has a unique archi tectural pattern and a distinctive molecular or cytogenetic profile. T he chief reason for their distinction from one another is the differen ce in their biologic behavior. Careful and thorough light microscopic examination distinguishes most cases based on individual characteristi c architectural and cytomorphologic features. However, precise charact erization may be difficult in some cases because of overlapping morpho logic features. We evaluated the antimitochondrial antibody 113-1 in a n attempt to ascertain differences in immunostaining patterns in 57 ca ses of granular renal tumors, including 20 renal oncocytomas, 15 chrom ophobe RCCs, 13 granular variants of clear cell RCC, and nine eosinoph ilic variants of papillary RCC. Distinctive, and nearly exclusive, sta ining patterns were observed among the groups, with chromophobe RCC sh owing peripheral accentuation of coarse cytoplasmic granules (15 of 15 ), renal oncocytoma with diffuse and fine granularity (20 of 20), and granular variant of clear cell RCC with irregular cytoplasmic distribu tion of coarse granules (11 of 13). Staining was most intense in the e osinophilic variant of papillary RCC and was generally coarsely granul ar and diffuse. Staining patterns also differed in clear cell areas wi thin chromophobe RCC and the granular variant of clear cell RCC. Altho ugh clear cells in the former group showed granular staining with peri pheral accentuation, most of the clear cells in the latter lacked any staining. We conclude that, in addition to distinct cytoarchitectural features, immunostaining patterns with antimitochondrial antibody 113- 1 appear to be a useful discriminatory adjunct in the complex differen tial diagnosis of granular renal cell tumors.