An exceptional case illustrating the malignant transformation of metanephric adenoma.

Metanephric tumors of kidney comprise a triad of benign tumors, namely metanephric adenoma (MA), fibroma, and adenofibroma, categorized based on the proportion of epithelial and/or stromal components. A review of published literature revealed only two cases of malignant transformation, both with sarcomatous transformation. We report an unusual case of malignant transformation in MA in a 35-year-old woman. Histopathologic examination of the mass showed areas reminiscent of benign metanephric tumors, which seamlessly merged with regions displaying high-grade carcinomatous/dedifferentiated features. To the best of our knowledge, this is the first reported case of MA with carcinomatous transformation. We propose expanding the spectrum of metanephric tumors of the kidney to include both carcinomatous and sarcomatous counterparts in future classifications.