Lesions sub-diagnostic of endometrioid intra-epithelial neoplasia/atypical hyperplasia: value of morphology and immunohistochemistry in predicting neoplastic outcome

AIMS

Areas of gland crowding that do not fulfil diagnostic criteria of endometrioid intra-epithelial neoplasia (EIN) are often encountered in endometrial biopsies. In this study, we document the prevalence of neoplastic outcome in patients with these subdiagnostic lesions (SL) and assess the utility of morphological features and a three-marker immunohistochemistry panel (PAX2, PTEN, beta-catenin) to predict outcome.

METHODS AND RESULTS

Of 430 women with SL on endometrial sampling at Brigham and Women's Hospital between 2001 and 2021 with available follow-up biopsy, 72 (17%) had a neoplastic outcome (EIN or endometrioid carcinoma). Multilayered epithelium and mitoses in SL were statistically associated with a neoplastic outcome. Abnormal three-marker staining was observed in 93% (53 of 57) of SL with neoplastic outcome and 60% (37 of 62) of a control group with benign outcome. Among the 72 patients with neoplastic outcome, EIN/carcinoma tissue was available in 33; of these, 30 (91%) showed abnormal staining for one or more markers. Remarkably, in 84% of these cases the EIN/carcinoma had the aberrant expression seen in the preceding SL. Based on a prevalence of 17%, the positive and negative predictive values of abnormal staining in one or more markers were 24 and 97%, respectively.

CONCLUSIONS

The presence of SL warrants clinical surveillance and repeat sampling because it is followed by endometrioid neoplasia in a significant subset of patients. Normal three-marker staining identifies women with a very low risk of neoplastic outcome. Conversely, abnormal staining is frequent in SL with benign outcome leading to poor specificity and positive predictive value.

Histopathologic and Genetic Features of Mismatch Repair-Deficient High-Grade Prostate Cancer

AIMS

Mismatch repair (MMR) deficiency is commonly caused by functional inactivation of MLH1, PMS2, MSH2 or MSH6. The morphologic and molecular correlates of MMR deficiency have been extensively characterized in certain tumor types such as colorectal and endometrial adenocarcinoma. In contrast, the histologic and molecular features of MMR-deficient prostate cancer remain incompletely described. In this study, we evaluated 19 MMR-deficient prostate cancers, including 11 cases without prior systemic treatment.

METHODS AND RESULTS

All treatment-naïve cases (11/11, 100%) were Grade Group 4-5 and had predominant cribriform and/or solid growth patterns. Solid components (any amount) and tumor infiltrating lymphocytes were seen in 7/11 (64%) of these cases each. In 68 MMR-proficient Grade Group 5 prostate cancers, predominant cribriform or solid growth patterns, solid components (any amount) and tumor infiltrating lymphocytes were seen at significantly lower frequencies (31/68, 46%; 9/68, 13% and 6/62, 9%, respectively; p<0.001 for all comparisons). Molecular evaluation of 19 cases demonstrated that MMR-deficiency was secondary to functional loss of MSH2/MSH6 and MLH1/PMS2 in 15 cases (79%) and 4 cases (21%), respectively. Definite or likely germline mutations were present in 4 cases (4/19, 21%). TMPRSS2::ERG rearrangements were identified in 2 cases (2/19, 11%). Recurrent cancer-relevant somatic mutations included (but were not limited to) ATM, TP53, FOXA1, RB1, BRCA2 and PTEN.

CONCLUSIONS

MMR deficiency was most commonly secondary to inactivation of MSH2/MSH6 in this study. Importantly, MMR-deficient high-grade prostatic adenocarcinomas had morphologic features that might be useful to identify selected cases for MMR IHC.

Low-Grade Fumarate Hydratase-Deficient Renal Cell Carcinoma in a 30-Year-Old Female

Fumarate hydratase (FH)-deficient renal cell carcinoma (RCC) is a rare and clinically aggressive RCC subtype that is commonly associated with the hereditary leiomyomatosis and renal cell carcinoma syndrome. The diagnostic hallmark of FH-deficient RCC is a high-grade microscopic appearance with prominent inclusion-like eosinophilic nucleoli and perinucleolar halos. Herein we report a case of an FH-deficient RCC in a 30-year-old female that exhibited low-grade nuclei and abundant eosinophilic cytoplasm, reminiscent of the clinically more indolent succinate dehydrogenase-deficient RCC subtype and the newly described eintity, eosinophilic, solid and cystic RCC. This case illustrates that FH-deficient RCC can have a wide spectrum of microscopic appearances, including low-grade eosinophilic RCC. In addition, it highlights that a low threshold to perform the immunohistochemical stains for FH and S-(2-succino) cysteine is warranted in RCC cases with unusual and even low-grade eosinophilic morphology.

Novel morphological and genetic features of fumarate hydratase deficient renal cell carcinoma in HLRCC syndrome patients with a tailored therapeutic approach

The hereditary leiomyomatosis and renal cell carcinoma syndrome (HLRCC) is defined by germline mutations in the fumarate hydratase (FH) gene and associated with leiomyomas and aggressive renal cell carcinomas with FH deficiency. Here, we comprehensively characterize two new patients with HLRCC syndrome on a morphological, immunohistochemical and genetic level. The patients developed aggressive HLRCC syndrome-associated RCCs, uterine leiomyomas and dermal leiomyomas. One HLRCC syndrome-associated RCC exhibited an unusual morphology with accumulation of "colloid-like" cytoplasmic inclusions, which might serve as a novel sentinel feature to trigger further testing. This case showed partially retained FH expression, initially hampering correct diagnosis. Comprehensive next-generation sequencing analyses of HLRCC syndrome-associated RCC and leiomyomas in our patients revealed divergent genetic changes in the FH gene in different tumors from the same patient. While all leiomyomas (uterine and cutaneous) showed a FH loss of heterozygosity (LOH) as a wildtype allele inactivating event, one HLRCC-RCC showed a second, undescribed NM_000143.3; c.947C>T; p.Ala316Val FH mutation accompanying the preexisting splice site mutation c.378+2T>C. In the other HLRCC syndrome-associated RCC, the FH mutation (NM_000143.3; c.462T>G; p.Asn154Lys with a somatic LOH) represents another variant of unknown significance that we link to HLRCC - and thus classify as likely pathogenic. Due to the specific diagnosis of metastatic HLRCC syndrome-associated RCC, both cases were treated in first line with bevacizumab/erlotinib and showed remarkable and long lasting responses. These findings allow new morphological and molecular insights into the biology of the HLRCC syndrome, corroborate the "second hit" hypothesis of tumor formation in HLRCC patients and may promote a distinct therapeutic approach.

Histological and molecular characterization of TFEB-rearranged renal cell carcinomas

The 2016 WHO Classification of Tumors of the Urinary System recognizes microphthalmia transcription factor (MiT) family translocation carcinomas as a separate entity among renal cell carcinomas. TFE3 and transcription factor EB (TFEB) are members of the MiT family for which chromosomal rearrangements have been associated with renal cell carcinoma formation. TFEB translocation renal cell carcinoma is a rare tumor harboring a t(6;11)(p21;q12) translocation. Recently, renal cell carcinomas with TFEB amplification have been identified. TFEB amplified renal cell carcinomas have to be distinguished from TFEB-translocated renal cancer, because they may demonstrate a more aggressive behavior. Herein, we present a TFEB-translocated and a TFEB-amplified carcinoma cases and describe their distinct histological, immunohistochemical, and molecular characteristics. In addition, we review conventional morphology, immunophenotype, genetic background, and clinical outcome of TFEB-rearranged RCCs in the literature, with a special emphasis on important differential diagnoses and the diagnostic approach.

Genome Editing in Human Cells Using CRISPR/Cas Nucleases

The clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated (Cas) system has been broadly adopted for highly efficient genome editing in a variety of model organisms and human cell types. Unlike previous genome editing technologies such as zinc finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs), CRISPR/Cas technology does not require complex protein engineering and can be utilized by any researcher proficient in basic molecular biology and cell culture techniques. This unit describes protocols for design and cloning of vectors expressing single or multiplex gRNAs, for transient transfection of human cell lines, and for quantitation of mutation frequencies by T7 endonuclease I assay. These protocols also include guidance for using two improvements that increase the specificity of CRISPR/Cas nucleases: truncated gRNAs and dimeric RNA-guided FokI nucleases.

Dimeric CRISPR RNA-Guided FokI-dCas9 Nucleases Directed by Truncated gRNAs for Highly Specific Genome Editing

Monomeric clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR associated 9 (Cas9) nucleases have been widely adopted for simple and robust targeted genome editing but also have the potential to induce high-frequency off-target mutations. In principle, two orthogonal strategies for reducing off-target cleavage, truncated guide RNAs (tru-gRNAs) and dimerization-dependent RNA-guided FokI-dCas9 nucleases (RFNs), could be combined as tru-RFNs to further improve genome editing specificity. Here we identify a robust tru-RFN architecture that shows high activity in human cancer cell lines and embryonic stem cells. Additionally, we demonstrate that tru-gRNAs reduce the undesirable mutagenic effects of monomeric FokI-dCas9. Tru-RFNs combine the advantages of two orthogonal strategies for improving the specificity of CRISPR-Cas nucleases and therefore provide a highly specific platform for performing genome editing.

GUIDE-seq enables genome-wide profiling of off-target cleavage by CRISPR-Cas nucleases

CRISPR RNA-guided nucleases (RGNs) are widely used genome-editing reagents, but methods to delineate their genome-wide, off-target cleavage activities have been lacking. Here we describe an approach for global detection of DNA double-stranded breaks (DSBs) introduced by RGNs and potentially other nucleases. This method, called genome-wide, unbiased identification of DSBs enabled by sequencing (GUIDE-seq), relies on capture of double-stranded oligodeoxynucleotides into DSBs. Application of GUIDE-seq to 13 RGNs in two human cell lines revealed wide variability in RGN off-target activities and unappreciated characteristics of off-target sequences. The majority of identified sites were not detected by existing computational methods or chromatin immunoprecipitation sequencing (ChIP-seq). GUIDE-seq also identified RGN-independent genomic breakpoint 'hotspots'. Finally, GUIDE-seq revealed that truncated guide RNAs exhibit substantially reduced RGN-induced, off-target DSBs. Our experiments define the most rigorous framework for genome-wide identification of RGN off-target effects to date and provide a method for evaluating the safety of these nucleases before clinical use.

Dimeric CRISPR RNA-guided FokI nucleases for highly specific genome editing

Monomeric CRISPR-Cas9 nucleases are widely used for targeted genome editing but can induce unwanted off-target mutations with high frequencies. Here we describe dimeric RNA-guided FokI nucleases (RFNs) that can recognize extended sequences and edit endogenous genes with high efficiencies in human cells. RFN cleavage activity depends strictly on the binding of two guide RNAs (gRNAs) to DNA with a defined spacing and orientation substantially reducing the likelihood that a suitable target site will occur more than once in the genome and therefore improving specificities relative to wild-type Cas9 monomers. RFNs guided by a single gRNA generally induce lower levels of unwanted mutations than matched monomeric Cas9 nickases. In addition, we describe a simple method for expressing multiple gRNAs bearing any 5' end nucleotide, which gives dimeric RFNs a broad targeting range. RFNs combine the ease of RNA-based targeting with the specificity enhancement inherent to dimerization and are likely to be useful in applications that require highly precise genome editing.