Papillary renal cell carcinoma (pRCC) is the second most common RCC subtype and can be further classified as type 1 (pRCC1) or 2 (pRCC2). There is currently minimal understanding of pRCC1 pathogenesis, and treatment decisions are mostly empirical. The aim of this study was to identify biological pathways that are involved in pRCC1 pathogenesis using an integrated genomic approach. By microarray analysis, we identified a number of significantly dysregulated genes and microRNAs (miRNAs) that were unique to pRCC1. Integrated bioinformatics analyses showed enrichment of the focal adhesion and extracellular matrix (ECM) pathways. We experimentally validated that many members of these pathways are dysregulated in pRCC1. We identified and experimentally validated the downregulation of miR‐199a‐3p in pRCC1. Using cell line models, we showed that miR‐199a‐3p plays an important role in pRCC1 pathogenesis. Gain of function experiments showed that miR‐199a‐3p overexpression significantly decreased cell proliferation (p = 0.013). We also provide evidence that miR‐199a‐3p regulates the expression of genes linked to the focal adhesion and ECM pathways, such as caveolin 2 (CAV2), integrin beta 8 (ITGB8), MET proto‐oncogene and mammalian target of rapamycin (MTOR). Using a luciferase reporter assay, we further provide evidence that miR‐199a‐3p overexpression decreases the expression of MET and MTOR. Using an integrated gene/miRNA approach, we provide evidence linking miRNAs to the focal adhesion and ECM pathways in pRCC1 pathogenesis. This novel information can contribute to the development of effective targeted therapies for pRCC1, for which there is none currently available in the clinic.

Aims: Sporadic renal cell carcinomas with fibromyomatous stroma (RCC FMS) with coexistent haemangioblastoma (HB)‐like morphology have been previously reported. Such morphology has not, however, been documented in patients with tuberous sclerosis complex (TSC). We evaluated clinicopathologic, immunohistochemical and molecular findings of RCC FMS with HB‐like features in three TSC patients.Methods and results: All three patients were females with confirmed germline mutations in TSC1 in the absence of VHL or other alterations. One patient had bilateral nephrectomy with six separate tumours (three in each kidney), and two patients had one tumour each, resected by partial nephrectomy. Prominent fibromuscular stroma was present at the tumoral periphery and surrounding clear cell nests forming tubules and papillary formations (RCC FMS areas), admixed with solid, clear to eosinophilic and spindle cell areas (HB‐like areas). HB‐like areas were variably represented in individual tumours, but in some, HB‐like features were almost exclusive. HB‐like areas were negative for CK7 and showed inhibin‐α and S100 reactivity, in contrast to typical RCC FMS areas, which were CK7 positive, while negative for inhibin‐α and S100. GPNMB, which is consistently expressed in TSC/mTOR altered tumours, was positive in both components. On follow‐up (10 months–21 years), all patients had an indolent course.Conclusions: HB‐like morphology found in RCC FMS in TSC patients represents part of the morphologic spectrum of RCC FMS, which is a previously underreported and underrecognized feature. RCC FMS with HB‐like areas show uniform GPNMB reactivity and are associated with TSC/MTOR alterations, but not with VHL alterations.

Papillary renal neoplasm with reverse polarity (PRNRP) is a recently described indolent entity with distinct features and its recognition from other oncocytic/eosinophilic papillary renal cell carcinoma (ePRCC) has important prognostic implications. ABCC2, a renal drug transporter, is overexpressed in aggressive PRCCs. In this study, we compared the clinicopathological parameters and the biological ABCC2 expression between PRNRP and ePRCC. PRNRP (n = 8) and ePRCC (n = 21) cases were selected from resection specimens and corresponding clinicopathological data were collected. ABCC2 immunohistochemical (IHC) staining was performed and ABCC2 staining patterns were classified as negative, cytoplasmic, and brush‐border. RNA in‐situ hybridization (ISH) was used to assess ABCC2 transcript levels. All eight PRNRP cases had weak cytoplasmic ABCC2 IHC reactivity; however, they showed no detectable ABCC2 transcripts on RNA ISH. In comparison, 76% (16/21) of ePRCCs showed ABCC2 IHC brush‐border expression and significantly higher ABCC2 RNA ISH transcript levels (p < 0.001). Additionally, the ePRCC group showed a significantly larger tumor size (p = 0.004), higher WHO/ISUP grade (p < 0.001), and stage (p = 0.044). None of the PRNRP cases showed disease progression, while 9.5% (2/21) ePRCCs had disease progression. PRNRP is clinically and biologically distinct from ePRCC. Hence, it is crucial to differentiate between these two entities, particularly in needle core biopsies.