Renal adenomas: pathological differential diagnosis with malignant tumors

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.

AMACR Positive Papillary Renal Adenomatosis and Multifocal Papillary Carcinoma in End Stage Renal Disease

Immunomarker α-methylacyl-coenzyme A racemase (AMACR), a protein involved in the metabolism of branched chain fatty acids was initially recognized in the evaluation of prostate cancer. AMACR is also a fairly sensitive marker for papillary renal cell carcinoma. Papillary adenoma associated with papillary renal cell carcinoma are AMACR positive and both represent a continuum of the same biological process. However, the papillary adenomas associated with end-kidney and/or acquired cystic disease are AMACR negative. Herein, we report a case of AMACR positive renal adenomatosis with tiny foci of papillary carcinoma in a background of end stage kidney disease and nephrolithiasis. AMACR staining pattern in renal papillary adenomas needs more evaluation to better understand their pathogenesis under different settings.

BRAF mutations in metanephric adenoma of the kidney

BACKGROUND

Metanephric adenoma (MA) of the kidney is a rare, indolent tumor that may be difficult to differentiate from other small renal masses (SRMs). Genetic alterations associated with MA remain largely unknown.

OBJECTIVE

We aimed at defining genetic events in MA of the kidney and determining their influence in the management of this disease.

DESIGN, SETTING, AND PARTICIPANTS

Multiplexed mass spectrometric genotyping was performed on 29 MA cases after tumor DNA extraction. We also conducted a mutational screen in an additional 129 renal neoplasms. Immunohistochemistry was performed on the MA cases to assess molecular markers of signaling pathway activation. Patients' baseline characteristics, as well as follow-up data, were captured.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

We used descriptive statistics for baseline clinical characteristics and incidence of mutations. The Wilcoxon rank-sum test was used to correlate patient characteristics with mutational status.

RESULTS AND LIMITATIONS

We identified the v-raf murine sarcoma viral oncogene homolog B1 (BRAF) V600E mutation in 26 of 29 MA cases. These results were validated in all cases using the commercially available BRAF Pyro Kit (QIAGEN). In contrast, BRAF mutations were rare in the other 129 non-MA renal neoplasms that were screened. We detected a BRAF mutation (V600E) in only one papillary renal cell carcinoma case. In all MA tumors, we documented expression of phosphorylated mitogen-activated protein kinase and phosphorylated extracellular signal-regulated kinase, accompanied by immunoreactivity for p16 (INK4a). All patients were treated with a partial or radical nephrectomy, and after a median follow-up of 26.5 mo, there were no local or distant recurrences. Limitations include the retrospective nature of this study.

CONCLUSIONS

BRAF V600E mutations are present in approximately 90% of all MA cases, serving as a potential valuable diagnostic tool in the differential diagnosis of SRMs undergoing a percutaneous biopsy. The presence of BRAF V600E and mitogen-activated protein kinase activation in a largely benign tumor supports the necessity for secondary events (e.g., p16 loss) in BRAF-driven oncogenesis.

[Renal oncocytoma in pregnancy--an unusual presentation of secondary hypertension]

INTRODUCTION

Renal oncocytoma accounts for 5-7% of primary renal neoplasms. It is usually, diagnosed in asymptomatic patients and is characterized by a benign behavior without invasion of adjacent tissues or metastasis. Diagnosis during pregnancy is uncommon and to date there have been only a few cases reported in the literature.

CASE REPORT

The authors present the case of a 32-year-old nulliparous woman with uncontrolled hypertension diagnosed at seven weeks gestation. She was referred to our institution at 24 weeks with superimposed pre-eclampsia complicated by acute pulmonary edema and hemodynamic instability requiring mechanical ventilatory support, fetal growth restriction and stillbirth. Etiological study of the hypertensive disorder performed in the postpartum period was consistent with renal oncocytoma.

CONCLUSION

The clinical behavior of renal oncocytoma remains poorly characterized during pregnancy and may lead to an adverse maternal and fetal outcome despite its theoretically benign behavior. It is essential to exclude a possible secondary cause of hypertension in cases that are difficult to control.

Native nephrectomy in transplant patients with autosomal dominant polycystic kidney disease

INTRODUCTION

This study examined the clinical indications and timing for native nephrectomy (NN), together with the associated pathological findings in transplant patients with autosomal dominant polycystic kidney disease (ADPKD) at our institute over a period of 20 years.

METHODS

A retrospective review was performed of ADPKD patients who had undergone both kidney transplantation and NN. Patients were identified from the kidney transplant database between 1988 and 2008 at Guy's and St Thomas' Hospital and the notes reviewed. All NN specimens were re-reviewed and reported according to current guidelines.

RESULTS

There were 157 kidney transplants performed for ADPKD (114 cadaveric and 43 living donor). Of these, 31 required NN (28 bilateral). The timing of NN was pre-transplant in 10 cases, at the time of the transplant in 1 case and post-transplant in 20 cases. The indications for NN were urinary tract infection (n=14, 45%), pain (n=12, 39%), tumour suspicion (n=3, 10%), haematuria (n=1, 3%) and space (n=1, 3%). Mortality in this NN series was 3%, with a 65% surgical morbidity rate. The length of hospital stay post-NN was significantly longer with open compared with laparoscopic techniques (p=0.003). There were two renal cell carcinomas (RCCs) in this series. Both patients presented with macroscopic haematuria (bilateral pT1a papillary RCCs in one case and a pT3b clear cell RCC in the other case). The incidence of RCC in this series of ADPKD transplant patients was 1.3%.

CONCLUSIONS

We have demonstrated that the majority of ADPKD patients do not require NN, with only 20% of our series undergoing this procedure. The timing of NN is variable and dictated by indication. NN was only required to make space for transplantation in one case (combined kidney and pancreas transplant). The main indications for NN were recurrent infection and pain, where NN can provide a successful outcome. Laparoscopic NN can be performed safely in patients with ADPKD. Haematuria in such patients should not be assumed to be of benign origin and requires exclusion of urinary tract malignancy as the incidence of RCC in this population is at least as common as in the general population.

FoxOs enforce a progression checkpoint to constrain mTORC1-activated renal tumorigenesis

mTORC1 is a validated therapeutic target for renal cell carcinoma (RCC). Here, analysis of Tsc1-deficient (mTORC1 hyperactivation) mice uncovered a FoxO-dependent negative feedback circuit constraining mTORC1-mediated renal tumorigenesis. We document robust FoxO activation in Tsc1-deficient benign polycystic kidneys and FoxO extinction on progression to murine renal tumors; murine renal tumor progression on genetic deletion of both Tsc1 and FoxOs; and downregulated FoxO expression in most human renal clear cell and papillary carcinomas, yet continued expression in less aggressive RCCs and benign renal tumor subtypes. Mechanistically, integrated analyses revealed that FoxO-mediated block operates via suppression of Myc through upregulation of the Myc antagonists, Mxi1-SRα and mir-145, establishing a FoxO-Mxi1-SRα/mir-145 axis as a major progression block in renal tumor development.

Metanephric adenoma of the kidney: an unusual diagnostic challenge

Although metanephric adenoma (MA) is a rare, benign neoplasm of epithelial cells, it is often difficult to distinguish this entity from other malignant neoplasms preoperatively. We report a case of a large renal mass for which preoperative diagnosis was indeterminate, with the differential diagnosis including Wilm’s tumor, MA, and papillary renal cell carcinoma (PRCC). Accurate postoperative differentiation of MA from PRCC is critical because adjuvant therapy is considered after surgical resection of PRCC tumors.