The Spectrum of Metanephric Adenofibroma and Related Lesions

Abstract

The authors report nine new metanephric adenofibroma (MAFs; previously termed nephrogenic adenofibroma) and 16 related tumors from the files of the National Wilms Tumor Study Group Pathology Center (NWTSGPC). All tumors contained a variable amount of a bland spindle cell stroma, which is essentially identical to the recently described metanephric stromal tumor (MST). Features that distinguish this stroma from congenital mesoblastic nephroma (CMN) include intratumoral angiodysplasia, concentric cuffing of entrapped tubules ("onion skinning"), and heterologous differentiation. The epithelial components of these lesions spanned a wide range of appearances. All tumors contained at least focally an inactive embryonal epithelium identical morphologically to metanephric adenoma (MA), and hence each case could be classified as containing MAF. The epithelium of nine tumors had this appearance throughout, and hence these were considered usual MAFs. The epithelium of four tumors demonstrated increased mitotic activity but was otherwise similar to MA. The epithelial component of seven tumors spanned a morphologic spectrum from inactive MA to malignant epithelial predominant Wilms tumor (WT), with gradual transitions noted in several cases. Five other tumors contained a carcinomatous component distinct from these lesions but identical morphologically to papillary renal cell carcinoma (PRCC). In one of these cases, this component had metastasized to the regional lymph nodes at the time of diagnosis. No tumor recurred during follow-up, although almost all patients received adjuvant therapy for WT regardless of their tumor's histology and NWTSGPC diagnosis. In conclusion, MAF is a biphasic tumor that spans the morphologic spectrum between benign pure stromal (MST) and pure epithelial (MA) lesions, and can merge with the morphology of WT, supporting the concept that these are all related lesions. A relationship to PRCC is also evident.

Renal Tumors of Childhood—A Histopathologic Pattern-Based Diagnostic Approach

“…In the differential diagnosis of WTs with stromal and epithelial components, Metanephric adenofibroma (MAF) needs to be considered, despite its rarity. MAFs show features of both MST and MA (as described above), including positive nuclear staining for WT1 in the epithelial component, and positive CD34 staining in the stromal component [104,105]. Furthermore, approximately 50% of MAFs carry the BRAF V600E mutation, although rare WTs may also harbor a BRAF mutation [18,61,106].…”

An “accidental” discovery: Incidentally found metanephric adenofibroma in a 5-year-old male trauma patient

“…However, patients can present with gross hematuria when a centrally located lesion penetrates the collecting system. Clinical presentation also includes pain, hypertension, and polycythemia owing to the tumor's production of erythropoietin [1] .…”

“…Rarely, MAF are associated with malignant neoplasms such as nephroblastoma or papillary renal cell carcinoma [1] . There was no histologic evidence of a nephroblastoma or a papillary renal cell carcinoma in this current case.…”

“…These neoplasms consist of metanephric adenoma, metanephric stromal tumor, and metanephric adenofibroma (MAF). MAF consists of both epithelial and stromal cells and has even been reported to merge with the morphology of Wilms tumor [1] . Less than 100 of these cases have been reported in the literature, appearing more often within pathology literature [2] .…”

Metanephric Adenofibroma in a young adult

“…Histopathologic examination reveals MAF to be a benign tumor that is composed of varying proportions of epithelial-stromal elements and immunohistochemistry can differentiate it from Wilms tumor and papillary renal cell carcinoma mainly using CK, vimentin, CD34 and cytokeratin 7 (3). Galluzzo ML (4) reported a case with simultaneous MAF, Wilms tumor and clear cell carcinoma, indicating a relationship between these tumors.…”