Metanephric Adenoma-Epithelial Wilms Tumor Overlap Lesions: An Analysis of BRAF Status

Am J Surg Pathol. 2019 Sep;43(9):1157-1169. doi: 10.1097/PAS.0000000000001240.

Abstract

Metanephric adenoma (MA) has historically been considered to represent a differentiated form of epithelial Wilms tumor (WT), based in part upon cases that morphologically overlap these 2 neoplasms. More recently, BRAF V600E mutations have been demonstrated in the majority of MAs but not in unselected or even epithelial-predominant WTs, suggesting 2 genetically distinct entities. However, no prior study has examined BRAF status in neoplasms with overlapping histologic features of epithelial WT and MA. We studied a cohort of 11 such overlapping lesions, 2 of which we considered morphologically to be otherwise typical MAs with unusually prominent mitotic activity and 9 of which we classified as epithelial WTs with areas resembling MA. Both mitotically active MAs demonstrated the BRAF V600E mutation. While the majority (5/9) of epithelial WTs with areas resembling MA were negative for BRAF V600E mutation, 4 such cases were positive. Two BRAF V600E mutation-positive WTs occurred in children. One case in a 6-year-old male was morphologically similar to the BRAF V600E mutation-positive adult cases and subsequently metastasized to the lungs; remarkably, the metastases then completely resolved on Braf targeted therapy. A second occurred in a 3-year-old girl whose posttherapy nephrectomy specimen's tumor was encapsulated and mitotically active like a typical WT, but also had more differentiated areas resembling MA. Immunohistochemistry for Braf V600E paralleled the molecular findings, demonstrating immunoreactivity in both the WT and MA-like areas of all 4 of these neoplasms. In summary, we demonstrate that BRAF V600E mutations are not entirely restricted to typical MA, as they may be seen in MAs showing mitotic activity along with a subset of epithelial-predominant WTs in adults and children that have foci which overlap morphologically with MA.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenoma / genetics*
  • Adenoma / pathology
  • Adolescent
  • Adult
  • Child
  • Child, Preschool
  • DNA Mutational Analysis
  • Female
  • Humans
  • Kidney Neoplasms / genetics*
  • Kidney Neoplasms / pathology
  • Male
  • Middle Aged
  • Mutation
  • Proto-Oncogene Proteins B-raf / genetics*
  • Wilms Tumor / genetics*
  • Wilms Tumor / pathology
  • Young Adult

Substances

  • BRAF protein, human
  • Proto-Oncogene Proteins B-raf