Cellular Metanephric Stromal Tumor in a Postmenopausal Woman

Abstract

Metanephric stromal tumor (MST) of the kidney is a rare pediatric neoplasm which has rarely been reported in adults. The authors present a case of MST, cellular type, an unreported variant, in a 56-year-old postmenopausal woman. The 9.0-cm tumor was solid, unencapsulated, and well circumscribed, with a firm homogeneous cut surface. The tumor was purely stromal with dense spindle-cell proliferations displaying prominent schwannoma-like architecture, intratumoral angiodysplasia, and entrapped native renal tubules with "onion-skin" tumor collarettes. The tumor stroma expressed CD34, estrogen, and progesterone and did not express desmin, smooth muscle actin, S-100, or TLE-1. Considering the characteristic morphology and immunophenotype, a diagnosis of "metanephric stromal tumor, cellular type," was made. This is an exceptionally rare disease manifestation in an adult patient and the first description of MST with such high stromal cellularity, making this case unique in both clinical and pathological presentation.

Metanephric stromal tumor with BRAF V600E mutation in an adult patient: Case report and literature review

“…There is no sex predilection with age ranging from 43 to 77 years (mean: 54 years). The clinical presentations are similar to those in pediatric patients, including abdominal pain or mass in 3 cases, hematuria in 1, and hypertension in 2 (3)(4)(5)(6). Hypertension as a symptom is uncommonly seen in MST, presenting in less than 10% of pediatric cases (2).…”

“…MST typically occurs in the first years of life (mean: 2 years) with only a few cases documented after 3 years ( 2 ). MST affecting adult patients is even rarer with only 6 cases (including the current one) have been described to date ( Table 1 ) ( 3 – 6 ). There is no sex predilection with age ranging from 43 to 77 years (mean: 54 years).…”

“…Adult MSTs exhibited identical histological features to those in pediatric patients. The tumors could be solid or mixed solid and cystic with size ranging from 2.5 to 21 cm (mean: 7.3cm) (3)(4)(5)(6). Morphologically, MST is typically a subtly infiltrative tumor composed of variably cellular, bland-looking, spindle cells embedded in a diffusely fibrous to focally myxoid stroma.…”

“…Both tumors can rarely occur primarily within the kidney and show bland, spindle to epithelioid cells infiltrating or entrapping native tubules with extensive sclerosis, and positivity for CD34 by immunostain (15,16). SEF usually shows immunoreactivity for MUC4 and harbors the characteristic (3)(4)(5)(6). Excision of the tumor is adequate therapy.…”

“…Metanephric stromal tumor (MST) is a rare, benign stromal neoplasm unique to the kidney that is thought to be part of a spectrum of metanephric family of tumors which also includes the epithelial lesion metanephric adenoma (MA) and the mixed stromal-epithelial lesion metanephric adenofibroma (MAF) (1). The vast majority of MSTs occur in children in their first three years (2), with only few cases involving adults have been documented (3)(4)(5)(6). Recently, several molecular studies have revealed that most pediatric MSTs have a BRAF V600E mutation (7,8).…”