Metanephric adenoma with BRAF V600K mutation and a doubtful radiological imaging: pitfalls in the diagnostic process

Niccolo Lenci,Pierfrancesco Bassi,Eros Scarciglia,Marco Racioppi,Vincenzo Fiorentino,Maurizio Martini,Giuseppe Palermo,Pierconti Francesco,Mattia Schino

doi:10.1007/s00795-020-00269-z

Abstract

Metanephric adenoma (MA) is an uncommon benign renal tumor whose histomorphological aspect resembles that of Wilms’ tumor and papillary renal cell carcinoma. From a diagnostic and therapeutic perspective, recognition of this entity is important as it has a more favorable clinical outcome compared with Wilms’ tumor and papillary renal cell carcinoma. MA should not be treated with nephrectomy if the tumor size is small, opting for a conservative treatment. However, the preoperative diagnosis of this disease is extremely challenging. The present study describes a case of this rare disease, showing an ambiguous radiological imaging and that only after a percutaneous biopsy, was defined as a MA and treated with partial nephrectomy. Moreover, the histological diagnosis of this case was partially complicated by the equivocal immunohistochemical analysis showing negativity for BRAF VE1 staining. Only the mutational analysis demonstrated the presence of the BRAF V600K mutation (for the first time described in a case of metanephric adenoma), highlighting the necessity of sequencing in case of MA with negativity for BRAF VE1 clone.

Highlights

Metanephric adenoma (MA) is a rare tumor, accounting for 0.2% of adult renal epithelial neoplasms [1]. It occurs most commonly in middle-aged women and is considered benign [2]. Radiological diagnosis of this benign tumor is typically difficult, and most MAs are misdiagnosed as renal cell carcinomas (RCCs) preoperatively
The preoperative Computed Tomograph (CT) revealed a solid oval hypodense neoformation with regular margins (Dmax 32 mm) without macroscopic adipose tissue located on the anterior side of the left kidney, in its middle portion
This neoformation was characterized by progressive impregnation of contrast and was slightly inhomogeneous, with more hyperdense thin components in the late phase of the dynamic study (Fig. 1)

Summary

Introduction

Metanephric adenoma (MA) is a rare tumor, accounting for 0.2% of adult renal epithelial neoplasms [1]. It occurs most commonly in middle-aged women and is considered benign [2]. Radiological diagnosis of this benign tumor is typically difficult, and most MAs are misdiagnosed as renal cell carcinomas (RCCs) preoperatively. Metanephric adenoma should be differentiated from Wilms’ tumor, oncocytoma and papillary RCC. Studies demonstrated that about 80–90% of MA have a BRAF V600E mutation, making this molecular alteration and the use of BRAF VE1 antibody helpful in the differential diagnosis [4]. We describe a clinical case along with its immunohistochemical, molecular

Methods

Results

Conclusion