We developed and benchmarked Exome Cancer Test v.2.0 (EXaCT-2), a novel whole-exome sequencing (WES) assay based on Agilent’s SureSelect hybrid-capture technology and expanded with custom probes targeting cancer-informative genomic regions. EXaCT-2 provides ~1,400 cancer genes with the depth of coverage typical of targeted panels, while achieving the genomic breadth to detect somatic copy number alterations (SCNAs), common cancer-related rearrangements, oncogenic viruses and B-cell receptor (BCR) clonotypes. Evaluated with a cancer patient cohort of 244 matched tumor/normal pairs and compared with clinically-validated results, EXaCT-2 achieved a mean sequencing depth of ~400× for critical cancer genes and ~100× for the remainder of the exome, with SCNA characterization showing improved boundary detection and overall segmentation. The assay demonstrated enhanced sensitivity for detecting sub-clonal, low-allele-frequency mutations missed by standard exome assays, such as mutations in GC-rich genes like KRAS. Analysis is performed by a modular, bespoke pipeline that leverages a workflow manager (Nextflow), in combination with containerized open-source tools. In addition to mutations and SCNAs, the pipeline reports common cancer rearrangements, hematologic oncogenic viruses, BCR clonotypes, and global molecular metrics, such as tumor mutational burden (TMB) and microsatellite instability (MSI). Collectively, these results establish EXaCT-2 as a comprehensive platform for integrated cancer genome profiling.

Endometrial carcinoma with intestinal differentiation/colorectal carcinoma-like (CRC-like) features is rare with few cases reported to date. Those described are mainly endometrioid carcinomas with intestinal differentiation. We report a case of high-grade endometrial carcinoma with serous and intestinal/CRC-like components. The gross, histologic, immunohistochemical, and molecular features are described for both components of the tumor in the initial diagnostic biopsy and subsequent resection specimen. The diagnosis of primary endometrial carcinoma with serous and CRC-like components is supported by immunohistochemical and molecular findings, as well as clinical workup. The rarity of this phenomenon poses diagnostic challenges. In addition, the literature is reviewed with specific emphasis on the molecular and pathologic features of mixed endometrial carcinomas, including those with intestinal/CRC-like features.

INTRODUCTION:Current literature lacks data regarding the influence of serous fluid volume (SFV) on next-generation sequencing (NGS) performed on malignant cases. In this study, we highlight the impact of SFV and other parameters influencing the outcome of NGS analysis. MATERIALS AND METHODS:We evaluated 827 samples of serous fluids from 607 patients. Of these, 72 samples underwent NGS analysis. Effusion volume, tumor cellularity, DNA, and RNA quality metrics, as well as clinicopathologic and molecular data were evaluated. Pleural fluid accounted for 56.3% of the fluid samples collected. The most common primary tumor site was gastrointestinal/pancreatobiliary, adenocarcinoma was the most common histologic type. Overall mean volume was 293 mL. The mean Qubit DNA of the 72 effusion samples that underwent NGS analysis was 14.3 ng/μL and mean Qubit RNA was 28.2 ng/μL. The mean Qubit DNA concentration increases in SFV up to 100 mL only. RESULTS:No correlation exists between SFV and mean tumor cellularity. In addition, 74.6% (50 of 67) of sequenced samples showed oncogenic drivers; KRAS was the most common driver followed by EGFR. Three cases displayed ALK fusions, and 1 case displayed NTRK1 fusion. The DNA yield is higher in SFV of 100 mL as a cutoff. Beyond 100 mL, there is no impact of SFV on DNA yield. SFV does not impact RNA yield and mean tumor cellularity. Effusion samples should be submitted for molecular testing despite low tumor cellularity. CONCLUSIONS:Our results as a pilot study are important in optimization of SFV for both diagnosis as well as NGS analysis for improving management.

2615 Background: The measurement of tumor mutational burden (TMB) is critical to select patients who are expected to respond to immune checkpoint inhibitors or immune-oncology (IO). The majority of the clinical guidelines on the interpretation & utility of TMB values are based on studies performed on lung cancer, setting a cutoff of 10. Laboratories that are using comprehensive genomic profiling (CGP) for tumor testing are reporting TMB values &/or interpretations (high/low) beyond lung cancer. Multiple studies have shown that the TMB signature is not universal, but rather tumor &/or even patient-specific. However, the pan-cancer trial for IO (KEYNOTE-158) failed to consider setting different cutoffs per tumor type. Currently, no major guidelines or consensus statements address the issue of reporting TMB as a biomarker beyond lung cancer. In the current study, the membership of the SEQUOIA (Sequencing & Oncology Informatics Academic Team) Consortium investigates the landscape of TMB values across multiple cancer types. Methods: We investigated TMB values in 11,670 patient samples (M = 6225; F= 5445) across 13 different tumor types & histological subtypes, including cancers with lung, colorectal, gastrointestinal, brain, prostate, pancreatic, biliary, endometrioid, ovarian, skin, hematological (CLL myeloma) & lymphoid origin. All samples were processed by a CGP panel of 523 genes. Multiple specimen types were included in the study consisting of tissue, blood, marrow, & lymph node. Results: The range of TMB values varied significantly across different cancer types & histological subtypes. The colorectal, melanoma & endometrial cancers have a wider range of TMB values (2-400 mutations/MB) relative to prostate, breast, myeloma, & serous cancers (0-30 mutations/MB). Along with the range, the mean, & median TMB values are also significantly varied across these tumor types. We also identified that a subset of patients exhibits high TMB (>30 mutations/MB) values across almost all types of cancer. Conclusions: TMB values & their association with response to immune checkpoint inhibitors are not very well studied in all cancer types, although a TMB cut-off of 10 mutations/MB was defined as TMB-high for FDA-approved IO in patients with unresectable or metastatic solid tumors. The range, mean, median, cut-offs & clinical interpretations of TMB-high & low for IO based therapies for different tumor types has not been well established. Our data confirm the wide range, mean, & median across different tumor types, & thus laboratories & oncologists need to be cautious in the clinical interpretation of TMB values for patient management. Future studies should assess responsiveness to IO in specific tumor types based on TMB value to determine tumor-specific TMB cutoff values.

Thyroid-like cholangiocarcinoma is a very uncommon variant of peripheral-type cholangiocarcinoma. To date, only 4 prior cases have been reported. The molecular features of this tumor have not been described. We report a case of a 60-year-old woman with a tumor that evolved over a period of 10 years. A left hepatectomy specimen showed an 11 cm tumor that on histology exhibited areas reminiscent of a thyroid tumor with follicular and insular features which were positive on immunohistochemistry for cytokeratin 7 and in-situ hybridization for albumin. A detailed molecular analysis failed to show mutations common to cholangiocarcinomas but revealed frameshift mutations in 2 chromatin-remodeling genes, CREBBP and KMNT2A. This case confirms that thyroid-like cholangiocarcinoma is a histologic variant of this tumor that is associated with relatively low growth. As most cholangiocarcinomas, it is diffusely positive for cytokeratin 7 and albumin by in-situ hybridization. Given its rarity, the molecular alterations in this specific histologic subtype remain to be fully elucidated.

To date, the apocrine variant of lobular carcinoma in situ (AP-LCIS) has been cursorily described as a subtype of lobular carcinoma in situ (LCIS). We retrospectively reviewed 34 cases of AP-LCIS (including 23 associated with invasive lobular carcinoma) to fully characterize it. AP-LCIS typically presented with screen-detected calcifications in older women (mean age: 65 y) and was characterized by distended terminal duct lobular units with relatively large "pleomorphic" cells, central necrosis, and calcifications. AP-LCIS cells exhibited abundant eosinophilic occasionally granular cytoplasm, hyperchromatic nuclei, and prominent nucleoli. Synchronous classic and/or florid LCIS was identified in 24/34 (70%) AP-LCIS, and in 9/11 (82%) pure AP-LCIS. Most (68%) cases of AP-LCIS were estrogen receptor-positive (50% strongly), 35% were progesterone receptor-positive, 26% were human epidermal growth factor 2-positive, 18% demonstrated high-proliferation rate (Ki67: >15%), and 90% were androgen receptor-positive. Aurora kinase A, immunoreactive in 38% of AP-LCIS cases, was not significantly associated with recurrence, development of invasion, or nodal positivity (P>0.05). Compared with conventional (nonapocrine) pleomorphic lobular carcinoma in situ (P-LCIS), aurora kinase A was expressed in a significantly greater proportion of P-LCIS (100%). AP-LCIS and P-LCIS did not otherwise differ in clinicopathologic features. Next-generation sequencing utilizing the Oncomine Comprehensive Panel v2, performed on 27 AP-LCIS cases, showed no specific molecular findings. In a mean follow-up of 57 months, 2 (of 11, 18%) pure AP-LCIS cases recurred (2 both in situ and invasive) and none metastasized or proved fatal. AP-LCIS should be regarded as another high-grade LCIS similar to P-LCIS in many respects, and pending additional studies should be managed similarly.