The impact of whole genome and transcriptome analysis (WGTA) on predictive biomarker discovery and diagnostic accuracy of advanced malignancies.

In this study, we evaluate the impact of whole genome and transcriptome analysis (WGTA) on predictive molecular profiling and histologic diagnosis in a cohort of advanced malignancies. WGTA was used to generate reports including molecular alterations and site/tissue of origin prediction. Two reviewers analyzed genomic reports, clinical history, and tumor pathology. We used National Comprehensive Cancer Network (NCCN) consensus guidelines, Food and Drug Administration (FDA) approvals, and provincially reimbursed treatments to define genomic biomarkers associated with approved targeted therapeutic options (TTOs). Tumor tissue/site of origin was reassessed for most cases using genomic analysis, including a machine learning algorithm (Supervised Cancer Origin Prediction Using Expression [SCOPE]) trained on The Cancer Genome Atlas data. WGTA was performed on 652 cases, including a range of primary tumor types/tumor sites and 15 malignant tumors of uncertain histogenesis (MTUH). At the time WGTA was performed, alterations associated with an approved TTO were identified in 39 (6%) cases; 3 of these were not identified through routine pathology workup. In seven (1%) cases, the pathology workup either failed, was not performed, or gave a different result from the WGTA. Approved TTOs identified by WGTA increased to 103 (16%) when applying 2021 guidelines. The histopathologic diagnosis was reviewed in 389 cases and agreed with the diagnostic consensus after WGTA in 94% of non-MTUH cases (n = 374). The remainder included situations where the morphologic diagnosis was changed based on WGTA and clinical data (0.5%), or where the WGTA was non-contributory (5%). The 15 MTUH were all diagnosed as specific tumor types by WGTA. Tumor board reviews including WGTA agreed with almost all initial predictive molecular profile and histopathologic diagnoses. WGTA was a powerful tool to assign site/tissue of origin in MTUH. Current efforts focus on improving therapeutic predictive power and decreasing cost to enhance use of WGTA data as a routine clinical test.

Immunohistochemistry Critical Assay Performance Controls (ICAPC) Reduce Interobserver Variability in the Interpretation of BRAFV600E Immunohistochemistry.

The utility of prognostic and predictive immunohistochemistry biomarkers in the context of cancer is plagued by inconsistent interpretation of results which can lead to poor rates of adoption or inappropriate use of novel therapeutic strategies. To monitor immunohistochemistry assay performance, a new on-slide control motif, Immunohistochemistry Critical Assay Performance Controls (ICAPC) was developed. We hypothesized that the use of these controls by the diagnosing pathologist to interpret BRAFV600E would result in reduced interobserver and intraobserver interpretation errors. A cross-sectional, sequentially obtained sample of surgical pathology cases stained for BRAFV600E was assembled from a single hospital in Vancouver, British Columbia. Half of the cases had normal on-slide controls and the remainder with ICAPC. Results from 6 independent and blinded readers were compared with each other and to the gold-standard pathologic diagnosis with the goal of demonstrating superior interrater agreement with ICAPC relative to standard on-slide controls. Cohen's κ was used to compute pair-wise reader agreements, whereas Fleiss' κ was used to compare to the gold standard. The implementation of ICAPC resulted in statistically significant improvements in the interobserver agreement of BRAF mutation status ascertained by BRAFV600E immunohistochemistry. Half of the readers demonstrated significant improvements in agreement with the gold-standard diagnosis with the addition of ICAPC. Across all readers, the mean increase in κ was 0.14 with a 95% confidence interval of 0.01-0.28 (P=0.04). This study demonstrates that the addition of ICAPC serves to significantly reduce interobserver variability in the assessment of BRAFV600E immunohistochemistry. As such, we recommend that this approach should be used as part of a comprehensive quality management strategy in the setting of histopathology.

Off-label use of common predictive biomarkers in gastrointestinal malignancies: a critical appraisal.

The use of immunohistochemistry (IHC) as a companion diagnostic is an increasingly important part of the case workup by pathologists and is often central to clinical decision making. New predictive molecular markers are constantly sought for to improve treatment stratification parallel to drug development. Unfortunately, official biomarker guidelines lag behind, and pathologists are often left hesitating when medical oncologists request off-labelled biomarker testing. We performed a literature review of five commonly requested off-label IHC predictive biomarkers in gastrointestinal tract (GIT) malignancies: HER2, mismatch repair (MMR), PD-L1, BRAF V600E and ROS1. We found that HER2 amplification is rare and poorly associated to IHC overexpression in extracolonic and extragastric GIT cancers; however in KRAS wild type colorectal cancers, which fail conventional treatment, HER2 IHC may be useful and should be considered. For MMR testing, more evidence is needed to recommend reflex testing in GIT cancers for treatment purposes. MMR testing should not be discouraged in patients considered for second line checkpoint inhibitor therapy. With the exception of gastric tumors, PD-L1 IHC is a weak predictor of checkpoint inhibitor response in the GIT and should be replaced by MMR in this context. BRAF inhibitors showed activity in BRAF V600E mutated cholangiocarcinomas and pancreatic carcinomas in non-first line settings. ROS1 translocation is extremely rare and poorly correlated to ROS1 IHC expression in the GIT; currently there is no role for ROS1 IHC testing in GIT cancers. Overall, the predictive biomarker literature has grown exponentially, and official guidelines need to be updated more regularly to support pathologists' testing decisions.