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Diagnosis: Metanephric adenoma

Metanephric adenoma (MA) and solid papillary renal cell carcinoma (s-PRCC) exhibit significant similarities, both being well-circumscribed tumours composed of tightly packed small cells arranged in solid sheets or ill-defined tubules, often presenting glomeruloid bodies, psammoma bodies and dystrophic calcification, and showing overlapping immunoreactivity for S100, CD57 and CK7. Most MA are non-encapsulated, whereas most s-PRCC show a thick fibrous pseudocapsule. MA cells have scanty cytoplasm and a high nuclear/cytoplasmic ratio in comparison to s-PRCC, where occasional tumour cells show abundant cytoplasm and high nuclear grade. Polypoid branching fronds are common in MA and very unusual in s-PRCC. MA are positive for WT1 and negative for EMA and alpha-methylacyl-CoA racemase (AMACR). s-PRCC are positive for EMA and AMACR and negative for WT1. Despite overlapping features, careful morphological and architectural evaluation should result in accurate diagnosis of most MA and s-PRCC. In challenging cases, IHC stains for WT1, EMA and AMACR may help in distinguishing these two entities (Mantoan Padilha M, et al. Metanephric adenoma and solid variant of papillary renal cell carcinoma: common and distinctive features. Histopathology. 2013;62(6):941-53. [PubMed link])

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References

• Fan H, Shao QQ, Li HZ, Xiao Y, Zhang YS. The Clinical Characteristics of Metanephric Adenoma: A Case Report and Literature Review. Medicine (Baltimore). 2016;95(21):e3486. [PubMed link]
• Kinney SN, Eble JN, Hes O, Williamson SR, Grignon DJ, Wang M, Zhang S, Baldrige LA, Martignoni G, Brunelli M, Wang L, Comperat E, Fan R, Montironi R, MacLennan GT, Cheng L. Metanephric adenoma: the utility of immunohistochemical and cytogenetic analyses in differential diagnosis, including solid variant papillary renal cell carcinoma and epithelial-predominant nephroblastoma. Mod Pathol. 2015;28(9):1236-48. [PubMed link]
• Sun Z, Kan S, Zhang L, Zhang Y, Jing H, Huang G, Yu Q, Wu J. Immunohistochemical phenotype and molecular pathological characteristics of metanephric adenoma. Int J Clin Exp Pathol. 2015;8(6):6031-6. [PubMed link]
• Chen L, Deng FM, Melamed J, Zhou M. Differential diagnosis of renal tumors with tubulopapillary architecture in children and young adults: a case report and review of literature. Am J Clin Exp Urol. 2014;2(3):266-72. [PubMed link]
• Mantoan Padilha M, Billis A, Allende D, Zhou M, Magi-Galluzzi C. Metanephric adenoma and solid variant of papillary renal cell carcinoma: common and distinctive features. Histopathology. 2013;62(6):941-53. [PubMed link]

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