Abstract
Metanephric adenoma (MA), a well-described renal neoplasm, usually behaves in a benign fashion. It may have areas that are morphologically similar to papillary renal cell carcinoma (RCC) type, or epithelial (tubular predominant) type Wilms' tumor. Prior immunohistochemical studies of MA have reported variable staining patterns. Alpha-methylacyl-CoA racemase (AMACR), a molecular marker for prostate carcinoma, has subsequently been found to be overexpressed in breast, colorectal and ovarian cancers, among others. Recent microarray analysis of renal tumors has shown an increase of AMACR mRNA levels in papillary RCC but not in other subtypes. We investigated the utility of immunohistochemical staining for AMACR, cytokeratin 7(CK7), CD57 and WT1 to differentiate between the above-mentioned three neoplasms. Immunohistochemical stains were performed on paraffin-embedded tissue sections from 25 papillary RCC, 10 MAs and eight Wilms' tumors. AMACR was positive in one (10%) of 10 MAs and 24 (96%) of 25 papillary RCC, while it was negative in all Wilms' tumors. CK7 was positive in 20 of 25 papillary RCCs, focally positive in one Wilms' tumor and was negative in all MAs. CD57 was positive in all six MAs that were stained, focally positive in one of 25 papillary RCC and one of eight Wilms' tumors. WT1 was positive in seven of 10 MAs, three of 25 papillary RCCs and all eight Wilms' tumors. In conclusion, diffuse and strong immunoreactivity for AMACR may be useful in differentiating papillary RCC from MA but a panel which includes AMACR, CK7 and CD57 is better in this differential diagnosis. AMACR is not helpful in differentiating MA from Wilms' tumor, but CD57 is helpful in this differential diagnosis. WT1 may be useful in separating Wilms' tumor from MA and papillary RCC but is not helpful in differentiating MA from papillary RCC.
Highlights
Metanephric adenoma (MA) shares features with papillary renal cell carcinoma (PRCC) type I, the solid variant[10] and the epithelial component of the epithelial type Wilms’ tumor without anaplasia (WT).[11]
All but one PRCC were diffusely positive for Alpha-methylacyl-CoA racemase (AMACR) (Figure 2b) with 21 showing strong staining and three cases being weakly positive
The expression of AMACR is not limited to the prostate since it is overexpressed in several malignant tumors of the colon, breast and ovary, among others.[30]
Summary
Metanephric adenoma (MA) is a relatively rare though well-described benign neoplasm of the kidney.[1,2,3,4,5,6,7] The previously published series suggest that MAs are related to the proximal tubule of the fetal kidney or nephrogenic rests, and both the histologic and ultrastructural features of this tumor suggest similarities to metanephric tubular epithelium.[1,8,9] Morphologically, MA shares features with papillary renal cell carcinoma (PRCC) type I, the solid variant[10] and the epithelial component of the epithelial (tubular predominant) type Wilms’ tumor without anaplasia (WT).[11]. The extent of immunolabeling was categorized embryonic kidney, ovaries and testes.[19] In renal into diffuse (staining in 50–100% of cells) or focal tumors, WT1 expression is seen in Wilms’ tumor, (staining in 5–50% of cells). Neoplasms scored as positive keratin with a molecular weight of 54 kD.[22] It is showed either diffuse or focal, strong nuclear known to be positive in tumors from various sites staining for WT1 and/or strong cytoplasmic staining including most cases of PRCC. Neoplasms scored as and biochemical activity are not known.[23] CD57 is negative showed less than 5% of cells with expressed in the proximal tubules in the adult cytoplasmic or nuclear staining for the abovekidney.[21] mentioned reagents
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