Reevaluation of metanephric stromal tumor two decades after it was named: A narrative review

The aim of this narrative review is to provide an overview and update of metanephric stromal tumor (MST). All English language studies published from January 1, 2000 to December 31, 2019 in PubMed, EBSCO, Elsevier ScienceDirect, Springer Link and Taylor & Francis databases were searched with the search terms “metanephric stromal tumor” for this review. Seventeen eligible case reports representing 47 patients according to inclusion and exclusion criteria were included in this study. The average age of the patients was under 4 years (range from 2 d to 56 y) and over half of the cases (52.1%, 25/47) are were diagnosed as MST by accident or during examinations for other diseases. Morphologically, tumor specimens of almost all cases presented concentric “onion-skin cuffing” or characteristic collarettes around renal tubules under low power. There were 79.2% (18/25) of patients exhibited BRAF V600E mutations. Immunohistochemistry (IHC) is characterized by CD34 (+), Vimentin (+), Desmin (−), S-100 (−), SMA (−). Most patients underwent surgeries, and no metastasis or recurrence was found except for one case. MST is a rare benign pediatric renal tumor with surgical treatment as the first choice. CT examinations and ultrasonography are two widely accepted techniques for the diagnosis of MST. Percutaneous renal biopsy (PRB) is an effective and accurate way of preoperative diagnosis, however, it is not recommended for children under 10 years or with a cystic mass in CT images. The relationship between BRAF V600E mutations and mild clinical manifestations of MST is in need of further verification by biological experiments and clinical studies.