Efficient Identification of Patients With NTRK Fusions Using a Supervised Tumor-Agnostic Approach

CONTEXT.—

The neurotrophic tropomyosin receptor kinase (NTRK) family gene rearrangements have been recently incorporated as predictive biomarkers in a "tumor-agnostic" manner. However, the identification of these patients is extremely challenging because the overall frequency of NTRK fusions is below 1%. Academic groups and professional organizations have released recommendations on the algorithms to detect NTRK fusions. The European Society for Medical Oncology proposal encourages the use of next-generation sequencing (NGS) if available, or alternatively immunohistochemistry (IHC) could be used for screening with NGS confirmation of all positive IHC results. Other academic groups have included histologic and genomic information in the testing algorithm.

OBJECTIVE.—

To apply some of these triaging strategies for a more efficient identification of NTRK fusions within a single institution, so pathologists can gain practical insight on how to start looking for NTRK fusions.

DESIGN.—

A multiparametric strategy combining histologic (secretory carcinomas of the breast and salivary gland; papillary thyroid carcinomas; infantile fibrosarcoma) and genomic (driver-negative non-small cell lung carcinomas, microsatellite instability-high colorectal adenocarcinomas, and wild-type gastrointestinal stromal tumors) triaging was put forward.

RESULTS.—

Samples from 323 tumors were stained with the VENTANA pan-TRK EPR17341 Assay as a screening method. All positive IHC cases were simultaneously studied by 2 NGS tests, Oncomine Comprehensive Assay v3 and FoundationOne CDx. With this approach, the detection rate of NTRK fusions was 20 times higher (5.57%) by only screening 323 patients than the largest cohort in the literature (0.30%) comprising several hundred thousand patients.

CONCLUSIONS.—

Based on our findings, we propose a multiparametric strategy (ie, "supervised tumor-agnostic approach") when pathologists start searching for NTRK fusions.

Papillary renal cell neoplasm with reverse polarity: A new subtype of renal tumour with favorable prognosis

INTRODUCTION

Papillary renal cell neoplasm with reverse polarity (PRNRP) has recently been recognized as an entity separate from the traditional classification of papillary renal cell carcinomas, due to its specific histopathological, immunophenotypic and molecular characteristics, as well as its indolent behavior.

MATERIAL AND METHODS

We provide 6 new cases and a review of the literature published until the present time, which comprises a total number of 104 cases.

RESULTS

Our PRNRP cases correspond to 5 men and one woman aged between 47 and 91 years. In 5 of the 6 cases, the PRNRP was an incidental finding in nephrectomy specimens. Nephrectomy had been indicated due to the presence of another renal tumor, except for one case, in which surgical intervention was indicated due to PRNRP. Our cases present mass sizes between 2 and 13 mm, as well as papillary histology with a monolayered lining of eosinophilic cells with low-grade nuclei in apical location. Immunohistochemically, they show a constant positivity for GATA3 and negativity for vimentin. KRAS mutations were identified in 50% of our cases. After a follow-up ranging between one and 60 months, 5 of the cases were still alive without recurrences or metastases, and one died from urothelial carcinoma.

CONCLUSIONS

Our cases agree with the clinical and pathological characteristics described in the PRNRP cases published to date. With the present study, we provide the first series of national cases corroborating the existence of well-defined and constant diagnostic criteria that allow PRNRP to be considered as a distinctive entity.

Clear cell clusters in the kidney: a rare finding that should not be misdiagnosed as renal cell carcinoma

Clear cytoplasm is a major characteristic feature of most malignant renal neoplasms. Benign clear cells in the renal parenchyma, usually histiocytes, can occasionally be found, but they are infrequently of an epithelial nature. We report histological, immunohistochemical, ultrastructural, and cytogenomic features of clear epithelial cell clusters incidentally found in four kidney specimens. Multiple microscopic clear cell clusters were present in the cortex, often in subcapsular location. They were composed of large epithelial cells with strikingly clear cytoplasm, without nuclear atypia, arranged in solid nests, and some tubules with narrow lumina. Immunohistochemically, they were positive for AE1AE3, PAX 8, EMA, kidney-specific cadherin, cytokeratin 7, E cadherin, and CD117, with focal immunoreactivity for CD10. Carbonic anhydrase IX, vimentin, and markers related to apoptosis and proliferation were negative. Ultrastructurally, the cytoplasms were enlarged and poor in organelles, showing ballooning degeneration. Array comparative genomic hybridization showed no chromosomal gains or losses. Clear cell clusters constitute a rare finding in the kidney and must be differentiated from benign lesions (ectopic adrenal tissue, osmotic tubulopathy, histiocytic clusters, renal adenomas) and renal cell carcinomas. Clear cell clusters appear to be generated from "endocrine-type" atrophic tubules whose cells are enlarged due to intracellular oedema. Immunohistochemistry shows a distal nephron phenotype with a limited expression of a proximal marker, CD10. Coexisting chronic renal disease or ischemic conditions seem to be related to the development of clear cell clusters. Pathological, ultrastructural, and cytogenomic features do not support a preneoplastic nature of this lesion, at least in the cases studied here.