ABSTRACT
The morphological differentiation between chromophobe renal cell carcinoma [RCC] and renal oncocytoma [RO] may be difficult. This study evaluates S100A1 protein as a new marker for the differentiation between these two tumors. We selected twenty cases; fifteen of which were typically diagnosed after routine histopathological staining by hematoxylin and eosin [7 chromophobe RCC and 8 RO] while the remaining five cases showed confusing cytomorphological features and uncertainly diagnosed. Immunoperoxidase technique using atni-S100A1 antibody carried out semiquantitavely in all cases displayed a strong cytoplasmic positive granularity in five typical RO, moderate immunopositivity in two typical RO and weak reactivity in on typical RO while all seven typical chromophobe RCC cases were immunonegative. Regarding uncertainly diagnosed cases, three were immunopositive for S100A1 antibody [one strong, one moderate and one weakly reactive] in the same pattern as typical RO while the remaining two cases were immunonegative like typical chromophobe RCC cases. From our study, we concluded that S100A1 may be a potentially powerful marker to differentiate the chromophobe RCC from RO particularly when these tumors are in doubt about routine histologic diagnosis