Whole-genome characterization of myoepithelial carcinomas of the soft tissue

Myoepithelial carcinomas (MECs) of soft tissue are rare and aggressive tumors affecting young adults and children, but their molecular landscape has not been comprehensively explored through genome sequencing. Here, we present the whole-exome sequencing (WES), whole-genome sequencing (WGS), and RNA sequencing findings of two MECs. Patients 1 and 2 (P1, P2), both male, were diagnosed at 27 and 37 yr of age, respectively, with shoulder (P1) and inguinal (P2) soft tissue tumors. Both patients developed metastatic disease, and P2 died of disease. P1 tumor showed a rhabdoid cytomorphology and a complete loss of INI1 (SMARCB1) expression, associated with a homozygous SMARCB1 deletion. The tumor from P2 showed a clear cell/small cell morphology, retained INI1 expression and strong S100 positivity. By WES and WGS, tumors from both patients displayed low tumor mutation burdens, and no targetable alterations in cancer genes were detected. P2's tumor harbored an EWSR1::KLF15 rearrangement, whereas the tumor from P1 showed a novel ASCC2::GGNBP2 fusion. WGS evidenced a complex genomic event involving mainly Chromosomes 17 and 22 in the tumor from P1, which was consistent with chromoplexy. These findings are consistent with previous reports of EWSR1 rearrangements (50% of cases) in MECs and provide a genetic basis for the loss of SMARCB1 protein expression observed through immunohistochemistry in 10% of 40% of MEC cases. The lack of additional driver mutations in these tumors supports the hypothesis that these alterations are the key molecular events in MEC evolution. Furthermore, the presence of complex structural variant patterns, invisible to WES, highlights the novel biological insights that can be gained through the application of WGS to rare cancers.

Molecular Evaluation of Low-grade Low-stage Endometrial Cancer With and Without Recurrence

Low-grade, low-stage endometrioid carcinomas (LGLS EC) demonstrate 5-yr survival rates up to 95%. However, a small subset of these tumors recur, and little is known about prognostic markers or established mutation profiles associated with recurrence. The goal of the current study was to identify the molecular profiles of the primary carcinomas and the genomic differences between primary tumors and subsequent recurrences. Four cases of LGLS EC with recurrence and 8 cases without recurrence were evaluated via whole-exome sequencing. Three of the 4 recurrent tumors were evaluated via Oncomine Comprehensive Assay. The resulting molecular profiles of the primary and recurrent tumors were compared. Two of the 3 recurrent cases showed additional mutations in the recurrence. One recurrent tumor included an additional TP53 mutation and the other recurrent tumor showed POLE and DDR2 kinase gene mutation. The POLE mutation occurred outside the exonuclease domain. PIK3CA mutations were detected in 4 of 4 primary LGLS EC with recurrence and in 3 of 8 disease-free cases. LGLS EC with recurrence showed higher MSIsensor scores compared with LGLS without recurrence. The level of copy number gains in LGLS EC with recurrence was larger than LGLS EC without recurrence. This pilot study showed 1 of 3 recurrent cases gained a mutation associated with genetic instability (TP53) and 1 of them also acquired a mutation in the DDR2 kinase, a potential therapeutic target. We also noted a higher level of copy number gains, MSIsensor scores and PIK3CA mutations in the primary tumors that later recurred.

Retrospective Evaluation of the Antibody Prevalence in Epilepsy and Encephalopathy (APE2) Score

BACKGROUND

Autoimmune encephalitis (AE) is a rare collection of disorders that present with a diverse and often nebulous set of clinical symptoms. Indiscriminate use of multi-antibody panels decreases their overall utility and predictive value. Application of a standardized scoring system may help reduce the number of specimens that generate misleading or uninformative results.

METHODS

The results of autoimmune encephalopathy, epilepsy, or dementia autoantibody panels performed on serum (n = 251) or cerebrospinal fluid (CSF) (n = 235) specimens from October 9th, 2016 to October 11th, 2019 were collected. Retrospective chart review was performed to calculate the Antibody Prevalence in Epilepsy and Encephalopathy (APE2) score for patients with an antibody above the assay-specific reference interval and to classify results as true or false positive.

RESULTS

Of the 486 specimens, 60 (12.3%) generated positive results for any AE antibody (6 CSF and 54 serum). After removing 2 duplicate specimens collected from a single patient, 10 of the remaining 58 were determined to be true positives and 8 contained neural-specific antibodies. Application of the APE2 score revealed that 89% of all true positives and 86% of specimens with neural-specific antibodies had a score ≥4. In contrast, 76% of false positives, 74% of clinically nonspecific antibodies, and 85% of the negative specimens had an APE2 score <4.

CONCLUSION

The APE2 score can improve the diagnostic utility of autoimmune encephalopathy evaluation panels.

Common germline-somatic variant interactions in advanced urothelial cancer

The prevalence and biological consequences of deleterious germline variants in urothelial cancer (UC) are not fully characterized. We performed whole-exome sequencing (WES) of germline DNA and 157 primary and metastatic tumors from 80 UC patients. We developed a computational framework for identifying putative deleterious germline variants (pDGVs) from WES data. Here, we show that UC patients harbor a high prevalence of pDGVs that truncate tumor suppressor proteins. Deepening somatic loss of heterozygosity in serial tumor samples is observed, suggesting a critical role for these pDGVs in tumor progression. Significant intra-patient heterogeneity in germline-somatic variant interactions results in divergent biological pathway alterations between primary and metastatic tumors. Our results characterize the spectrum of germline variants in UC and highlight their roles in shaping the natural history of the disease. These findings could have broad clinical implications for cancer patients.

Acral fibromyxoma with loss of Rb1 by immunohistochemistry and fluorescence in situ hybridization: A diagnostically exploitable marker

Acral fibromyxoma (AF) is a slow growing benign soft tissue tumor with predilection to subungal and periungal region of the hands or feet. CD34 is consistently expressed whereas very recently loss of Rb1 expression was described as a possible driver molecular event for this entity. Herein we present two additional cases of AF with loss of Rb1 expression by IHC and subsequent confirmation of loss of the RB1 gene locus by fluorescence in situ hybridization (FISH). We hope to raise awareness in dermatopathology community of this new discovery, which can be diagnostically exploitable for this distinct and probably underreported neoplasm.

Delta-like protein 3 expression and therapeutic targeting in neuroendocrine prostate cancer

Histologic transformation to small cell neuroendocrine prostate cancer occurs in a subset of patients with advanced prostate cancer as a mechanism of treatment resistance. Rovalpituzumab tesirine (SC16LD6.5) is an antibody-drug conjugate that targets delta-like protein 3 (DLL3) and was initially developed for small cell lung cancer. We found that DLL3 is expressed in most of the castration-resistant neuroendocrine prostate cancer (CRPC-NE) (36 of 47, 76.6%) and in a subset of castration-resistant prostate adenocarcinomas (7 of 56, 12.5%). It shows minimal to no expression in localized prostate cancer (1 of 194) and benign prostate (0 of 103). DLL3 expression correlates with neuroendocrine marker expression, RB1 loss, and aggressive clinical features. DLL3 in circulating tumor cells was concordant with matched metastatic biopsy (87%). Treatment of DLL3-expressing prostate cancer xenografts with a single dose of SC16LD6.5 resulted in complete and durable responses, whereas DLL3-negative models were insensitive. We highlight a patient with neuroendocrine prostate cancer with a meaningful clinical and radiologic response to SC16LD6.5 when treated on a phase 1 trial. Overall, our findings indicate that DLL3 is preferentially expressed in CRPC-NE and provide rationale for targeting DLL3 in patients with DLL3-positive metastatic prostate cancer.

Integrative Molecular Analysis of Patients With Advanced and Metastatic Cancer

PURPOSE

We developed a precision medicine program for patients with advanced cancer using integrative whole-exome sequencing and transcriptome analysis.

PATIENTS AND METHODS

Five hundred fifteen patients with locally advanced/metastatic solid tumors were prospectively enrolled, and paired tumor/normal sequencing was performed. Seven hundred fifty-nine tumors from 515 patients were evaluated.

RESULTS

Most frequent tumor types were prostate (19.4%), brain (16.5%), bladder (15.4%), and kidney cancer (9.2%). Most frequently altered genes were TP53 (33%), CDKN2A (11%), APC (10%), KTM2D (8%), PTEN (8%), and BRCA2 (8%). Pathogenic germline alterations were present in 10.7% of patients, most frequently CHEK2 (1.9%), BRCA1 (1.5%), BRCA2 (1.5%), and MSH6 (1.4%). Novel gene fusions were identified, including a RBM47-CDK12 fusion in a metastatic prostate cancer sample. The rate of clinically relevant alterations was 39% by whole-exome sequencing, which was improved by 16% by adding RNA sequencing. In patients with more than one sequenced tumor sample (n = 146), 84.62% of actionable mutations were concordant.

CONCLUSION

Integrative analysis may uncover informative alterations for an advanced pan-cancer patient population. These alterations are consistent in spatially and temporally heterogeneous samples.

TET2 Deficiency Causes Germinal Center Hyperplasia, Impairs Plasma Cell Differentiation, and Promotes B-cell Lymphomagenesis

TET2 somatic mutations occur in ∼10% of diffuse large B-cell lymphomas (DLBCL) but are of unknown significance. Herein, we show that TET2 is required for the humoral immune response and is a DLBCL tumor suppressor. TET2 loss of function disrupts transit of B cells through germinal centers (GC), causing GC hyperplasia, impaired class switch recombination, blockade of plasma cell differentiation, and a preneoplastic phenotype. TET2 loss was linked to focal loss of enhancer hydroxymethylation and transcriptional repression of genes that mediate GC exit, such as PRDM1. Notably, these enhancers and genes are also repressed in CREBBP-mutant DLBCLs. Accordingly, TET2 mutation in patients yields a CREBBP-mutant gene-expression signature, CREBBP and TET2 mutations are generally mutually exclusive, and hydroxymethylation loss caused by TET2 deficiency impairs enhancer H3K27 acetylation. Hence, TET2 plays a critical role in the GC reaction, and its loss of function results in lymphomagenesis through failure to activate genes linked to GC exit signals. SIGNIFICANCE: We show that TET2 is required for exit of the GC, B-cell differentiation, and is a tumor suppressor for mature B cells. Loss of TET2 phenocopies CREBBP somatic mutation. These results advocate for sequencing TET2 in patients with lymphoma and for the testing of epigenetic therapies to treat these tumors.See related commentary by Shingleton and Dave, p. 1515.This article is highlighted in the In This Issue feature, p. 1494.