Adult metanephric adenoma presumed to be all benign? A clinical perspective

Metanephric Adenoma: A Case Report of a Rare Epithelial Renal Tumor

Metanephric adenoma (MA) is a rare embryonal epithelial tumor that is often diagnosed incidentally. A definitive diagnosis can only be made postoperatively based on the pathological findings. This case report discusses the rare occurrence of a metanephric adenoma, the symptoms it can present with, and the diagnosis, treatment, and immunological staining needed to differentiate metanephric adenoma from other types of renal tumors. In this study, a 37-year-old female presented to the emergency room for vague right lower quadrant pain (RLQ) and underwent imaging that showed a lesion on the lower pole of the left kidney. A subsequent biopsy of the lesion showed a low-grade renal epithelial neoplasm favoring metanephric adenoma. The patient successfully underwent a left partial nephrectomy to remove the tumor, which required no further treatment after resection. Due to the rarity of the tumor, it requires immunohistology to differentiate from other renal tumors such as Wilm's tumor and renal cell carcinoma. This case report aims to recognize proper workup, diagnosis, and treatment to achieve a positive outcome in the setting of this rare tumor.

BRAF Exon 15 Mutations in the Evaluation of Well-Differentiated Epithelial Nephroblastic Neoplasms in Children: A Report From the Children's Oncology Group Study AREN03B2

CONTEXT.—

The distinction between well-differentiated epithelial favorable-histology Wilms tumor (EFHWT) and metanephric adenoma (MA) in children has historically been determined by the required absence of both a fibrous pseudocapsule and mitotic activity in MA. More recently these features have been allowed in adult MA. Mutations in exon 15 of the BRAF gene are reported in up to 88% of MAs but have not been reported in EFHWTs.

OBJECTIVE.—

To clarify the pathologic and molecular features used to distinguish between pediatric MA and EFHWT.

DESIGN.—

Stage I epithelial tumors classified as EFHWT on central review (36 patients) were identified from the Children's Oncology Group AREN03B2 study. Thirteen tumors had morphologic features overlapping those of MA and 23 lacked such features; 35 of 36 had tissue available for sequencing of BRAF.

RESULTS.—

Patients with EFHWTs with MA features (13) were older (mean, 8.4 versus 1.9 years; P < .001), had smaller tumor diameters (mean, 6.0 versus 9.7 cm; P < .001), and had fewer mitoses (mean, 1 versus 48 mitoses per 10 high-power fields; P < .001) than patients with EFHWT lacking MA features (23). All EFHWTs with MA features contained at least a partial fibrous pseudocapsule; 7 of 12 (58%) had BRAF exon 15 mutation. No BRAF exon 15 mutations were identified in 23 EFHWTs lacking MA features. None of the 13 EFHWT patients with MA features have experienced relapse (median follow-up 5.9 years).

CONCLUSIONS.—

Pediatric epithelial neoplasms with features of MA that show partial encapsulation and/or modest mitotic activity may be classified as MAs. Although BRAF mutation supports the diagnosis of MA, it is not required for the diagnosis.

Atypical metanephric adenoma: Shares similar histopathological features and molecular changes of metanephric adenoma and epithelial-predominant Wilms’ tumor

Background

Metanephric adenomas (MAs) are rare, benign renal tumors. Wilms’ tumors (WTs) are malignant embryonic tumors that originated from nephrogenic blastemal cells. However, some tumors have similar morphology to both MA and epithelial-predominant WT, which makes differential diagnosis difficult. We aimed to analyze the morphological, immunophenotypic and molecular changes in overlapping cases to explore their attribution.

Methods and results

Twenty MAs, ten WTs, and nine cases with MA/WT overlapping histological features were studied. Twenty tumors demonstrated the typical morphological spectrum of MA with high cellularity and were composed of tightly packed small, uniform, round acini with a lower Ki67 index. Almost all MAs (94.7%, 18/19) were detected with BRAF V600E mutation. The ten WTs were epithelial-predominant WTs with glands, rosettes and glomerular structures, which also showed a higher Ki-67 index (up to 60%), invasive growth patterns, and a lack of BRAF mutation. However, the other nine overlapping cases showed two components: typical MA-like areas and epithelial WT-like areas. The cells of the WT-like areas were tubular, columnar and showed marked cytological atypia, with a Ki-67 proliferative index of up to 30%. The immunophenotype of these overlapping lesions was not significantly different from that of typical MA and they positively expressed WT1 and CD57. The BRAF V600E mutation was detected in both WT-like and MA-like areas in nine overlapping tumors. The follow-up data of 31 patients were analyzed, with a median follow-up time of 66 months (range, 8-45 months). Even though most patients with WT underwent radiotherapy or chemotherapy after surgery, two died, and one had liver metastasis. No MA or overlapping cases showed any evidence of recurrence or metastasis after surgery.

Conclusions

The molecular changes in tumors with overlapping morphological features were the same as those of typical MA; thus, we think that these tumors should be classified as MA and further called atypical MA. It is important to note that atypical MA is not a neglected subtype of MA. It possesses different histological morphology and a higher Ki-67 index but has the common imaging characteristics, immunophenotype and gene expression as typical MA, and patients usually have a good prognosis.

Adenoma metanéfrico: diagnóstico diferencial del carcinoma urotelial del tracto urinario superior. Reporte de un caso

Introduction: Metanephric adenoma is a rare benign kidney tumor. Patients with these tumors are usually asymptomatic, although polycythemia occurs in up 12% of cases. These masses are often described on diagnostic imaging as solid, single, well-defined, oval-shaped, unilateral lesions, located primarily in the renal medulla and without extrarenal involvement. These neoplasms are difficult to differentiate from malignant neoplasms of the upper urinary tract, so the definitive diagnosis is achieved by histopathology. Currently, the treatment of choice is radical nephrectomy. Case presentation: A 51-year-old woman from Bogotá (Colombia) was referred to the urology service of a tertiary care hospital due to bilateral lumbar pain of non-specific characteristics. At the time of consultation, the patient was asymptomatic. Renal and urinary tract ultrasound showed hydronephrosis and right renal mass. Computed tomography urography was requested, which revealed a lesion in the right renal pelvis with parenchymal invasion highly suggestive of high-risk upper urinary tract urothelial carcinoma, as well as adenopathies in the para-aortic lymph nodes. The patient underwent a radical nephroureterectomy with bladder cuff, which allowed establishing a final diagnosis of metanephric adenoma according to the histopathological study. Conclusions: Metanephric adenoma is a rare tumor that is difficult to diagnose through imaging, so it is necessary to explore additional tools to establish an accurate pre-surgical diagnosis that allows preserving the affected renal unit. Also, given their non-specificity, these tumors should be included in the differential diagnosis of lesions suggestive of upper tract urothelial carcinoma.

Key Renal Neoplasms With a Female Predominance

Renal neoplasms largely favor male patients; however, there is a growing list of tumors that are more frequently diagnosed in females. These tumors include metanephric adenoma, mixed epithelial and stromal tumor, juxtaglomerular cell tumor, mucinous tubular and spindle cell carcinoma, Xp11.2 (TFE3) translocation-associated renal cell carcinoma, and tuberous sclerosis complex (somatic or germline) associated renal neoplasms. The latter category is a heterogenous group with entities still being delineated. Eosinophilic solid and cystic renal cell carcinoma is the best-described entity, whereas, eosinophilic vacuolated tumor is a proposed entity, and the remaining tumors are currently grouped together under the umbrella of tuberous sclerosis complex/mammalian target of rapamycin-related renal neoplasms. The entities described in this review are often diagnostic considerations when evaluating renal mass tissue on biopsy or resection. For example, Xp11.2 translocation renal cell carcinoma is in the differential when a tumor has clear cell cytology and papillary architecture and occurs in a young or middle-aged patient. In contrast, tuberous sclerosis complex-related neoplasms often enter the differential for tumors with eosinophilic cytology. This review provides an overview of the clinical, gross, microscopic, immunohistochemical, genetic, and molecular alterations in key renal neoplasms occurring more commonly in females; differential diagnoses are also discussed regardless of sex predilection.

KANK1-NTRK3 fusions define a subset of BRAF mutation negative renal metanephric adenomas

Background

Metanephric adenoma (MA) is a rare benign renal neoplasm. On occasion, MA can be difficult to differentiate from renal malignancies such as papillary renal cell carcinoma in adults and Wilms̕ tumor in children. Despite recent advancements in tumor genomics, there is limited data available regarding the genetic alterations characteristic of MA. The purpose of this study is to determine the frequency of metanephric adenoma cases exhibiting cytogenetic aberration t (9;15)(p24;q24), and to investigate the association between t (9,15) and BRAF mutation in metanephric adenoma.

Methods

This study was conducted on 28 archival formalin fixed paraffin-embedded (FFPE) specimens from patients with pathologically confirmed MA. Tissue blocks were selected for BRAF sequencing and fluorescent in situ hybridization (FISH) analysis for chromosomal rearrangement between KANK1 on chromosome 9 (9p24.3) and NTRK3 on chromosome 15 (15q25.3), which was previously characterized and described in two MA cases.

Results

BRAF^V600E mutation was identified in 62% of our cases, 9 (38%) cases were BRAF^WT, and 4 cases were uninformative. Of the 20 tumors with FISH results, two (10%) were positive for KANK1-NTRK3 fusion. Both cases were BRAF^WT suggesting mutual exclusivity of BRAF^V600E and KANK1-NTRK3 fusion, the first such observation in the literature.

Conclusions

Our data shows that BRAF mutation in MA may not be as frequent as suggested in the literature and KANK-NTRK3 fusions may account for a subset of BRAF^WT cases in younger patients. FISH analysis for KANK1-NTRK3 fusion or conventional cytogenetic analysis may be warranted to establish the diagnosis of MA in morphologically and immunohistochemically ambiguous MA cases lacking BRAF mutations.

Experience of diagnosis and management of metanephric adenoma: retrospectively analysis of 10 cases and a literature review

Background

Metanephric adenoma (MA) is a rare benign tumor with only several hundred cases reported worldwide to date. Herein, we retrospectively summarized the experience of diagnosis and management of ten MA cases.

Methods

A total of ten MA patients were included in this study definitely diagnosed by postoperative immunohistochemistry at the First Affiliated Hospital of Nanjing Medical University from January 2010 to January 2019. Clinical characteristics, image features, therapeutic procedures, histological diagnosis and outcomes of them were retrospectively analyzed.

Results

Characteristics of the patient population were nine females and one male with age of 36.8±17.5 years. The mean tumor size was 33.6 mm (range from 35.0 to 70.0 mm). Among them, nine cases were asymptomatic and one case showed acute flank pain. All ten cases underwent plain and enhanced computed tomography (CT) scan. Laparoscopic partial nephrectomy (LPN) was performed in seven cases and laparoscopic radical nephrectomy (LRN) was applied in the other three cases. Postoperative routine pathology results confirmed that seven cases were MA. However, two patients were misdiagnosed with papillary renal cell carcinoma (PRCC), and another was misdiagnosed with Wilms’ tumor. Further immunohistochemistry eventually confirmed all these ten cases as MA. During a mean follow-up of 58.3 month, all ten patients were alive with no local recurrences nor metastases.

Conclusions

In summary, MA is a rare benign tumor with no distinct clinical symptoms. The definite diagnosis depends on the postoperative pathological findings. Fortunately, due to its non-malignant nature, patients always have a good prognosis.

Metanephric Adenoma with cystic changes- An uncommon presentation of a rare tumor in a young adult

Metanephric adenoma (MA) is a rare benign neoplasm of the kidney that is usually asymptomatic and incidentally diagnosed. MA usually present as a solid mass; however, a cystic presentation has been reported. The main differential diagnosis of MA is the epithelial predominant Wilms tumor (e-WT) and the solid variant of papillary renal cell carcinoma (pRCC). The presence of the BRAF gene mutation has recently been reported in 85% of MA, and less than 10% of cases of MA do not express this specific gene mutation. Herein we report a 22-year-old man who presented with back pain and abdominal discomfort with a renal mass on the computed tomographic scan. The diagnosis of metanephric adenoma was confirmed histopathologically. In our case, the tumor presented as a solid and cystic mass hence mimicking a papillary renal cell carcinoma. The VE1 protein, which correlates with BRAF gene mutation, did not show any significant expression. We want to highlight that MA can present as a cystic lesion that should be taken into account to avoid unnecessary radical nephrectomy. Also, we demonstrated that a subset of MA might not harbor the BRAF gene and, they are classified as the BRAF wild type MA.

Molecular characterisation of metanephric adenomas beyond BRAF: genetic evidence for potential malignant evolution

AIMS

Metanephric adenomas (MAs) are conventionally regarded as rare renal tumours with indolent behaviour; limited case reports have described MAs with aggressive features. Conventional MAs harbour hotspot BRAF V600E mutations. A BRAF V600E senescence pathway, mediated by cyclin-dependent kinase inhibitor 2A (CDKN2A)/p16, has been proposed to confer MA benignity. Aside from BRAF, the molecular landscape in both conventional MAs and those with aggressive features has not been fully characterised. The aim of this study was to molecularly profile a series of MAs to investigate the correlation between genomic findings and clinical outcome.

METHODS AND RESULTS

We retrospectively examined the histomorphology and patient outcomes of 11 conventional MAs and one MA with aggressive features. Each was subjected to capture-based next-generation DNA sequencing of 479 cancer-related genes and immunohistochemical profiling. All tumours were positive for WT1 immunostaining and BRAF V600E mutation. One conventional MA contained an additional somatic BRCA2 pathogenic mutation. The MA with aggressive features had a biphasic appearance: one component was epithelial, with areas morphologically consistent with conventional MA; the second component was sarcomatous, with areas of solid and angiosarcomatous growth. Differential profiling of the two populations revealed identical BRAF, EIF1AX and TERT promoter hotspot mutations in the epithelial and sarcomatous components. Deep deletion of CDKN2A and MYC amplification were identified only in the sarcomatous component.

CONCLUSIONS

Although the vast majority of MAs show indolent behaviour, rare pathogenic alterations can occur in conventional MAs in addition to BRAF. Molecular profiling of a case with aggressive clinical and pathological features shows genetic evidence for malignant evolution in MAs.

The findings of CT and MRI in patients with metanephric adenoma

Background

Metanephric adenoma (MA) is a benign renal tumor that is difficult to distinguish from a malignant tumor via traditional radiography. The diagnosis of MA is often dependent on postsurgical histopathological examination. In the present report, the imaging features of MA on computer tomography (CT) and magnetic resonance imaging (MRI) were retrospectively evaluated.

Methods

Eight MA patients, 17–67 years of age, were pathologically confirmed and recruited between April 2009 and November 2014. Four of the eight patients were female. All patients underwent CT scanning, and one patient underwent MRI scanning. Three patients underwent CTA of the renal arteries. All patients underwent resection surgery (radical nephrectomy in five and nephron-sparing surgery in three patients).

Results

The average tumor size was 44.0 ± 23.6 mm. The lesions in 87.5 % cases were located both in the renal cortex and medulla and exhibited exophytic growth. Plain CT showed that MA tumors were solid, and the average CT value was 37.9 ± 6.7 HU. Dynamic contrast-enhanced CT revealed that enhanced degrees of MA tumors in the renal cortex, renal parenchymal, and pelvic phase were all lower than that of normal renal parenchyma. A slight enhancement in the renal cortex phase and an even higher enhancement in the renal parenchymal phase were observed in seven of the cases. Progressive enhancement in the pelvic phase was found in five cases and a slight decreased enhancement in the pelvic phase in two cases. MRI revealed that MA tumor was isointense on T1WI and isointense on T2WI with some slightly hyperintense areas in the center. CTA of the renal arteries revealed the nutrient artery in one patient and no nutrient artery in two. Immunohistochemical experiments demonstrated that most tumor cells were positive for vimentin, CK, and EMA.

Conclusions

MA is a rare benign renal neoplasm. Detailed knowledge of the CT and MRI characteristics of MA plays an important role in MA diagnosis and treatment.