The Blueprint PD-L1 IHC Assay Comparison Project revealed that three of the four assays were closely aligned on tumor cell staining whereas the fourth showed consistently fewer tumor cells stained. All of the assays demonstrated immune cell staining, but with greater variability than with tumor cell staining. By comparing assays and cutoffs, the study indicated that despite similar analytical performance of PD-L1 expression for three assays, interchanging assays and cutoffs would lead to "misclassification" of PD-L1 status for some patients. More data are required to inform on the use of alternative staining assays upon which to read different specific therapy-related PD-L1 cutoffs.

Introduction: A grading system for pulmonary adenocarcinoma has not been established. The International Association for the Study of Lung Cancer pathology panel evaluated a set of histologic criteria associated with prognosis aimed at establishing a grading system for invasive pulmonary adenocarcinoma. Conclusions: A grading system based on the predominant and high-grade patterns is practical and prognostic for invasive pulmonary adenocarcinoma.

The CGG repeat in the 5' untranslated region of the fragile X mental retardation 1 gene (FMR1) exhibits remarkable instability upon transmission from mothers with premutation alleles. A collaboration of 13 laboratories in eight countries was established to examine four issues concerning FMR1 CGG-repeat instability among females with premutation (approximately 55-200 repeats) and intermediate (approximately 46-60 repeats) alleles. Our central findings were as follows: (1) The smallest premutation alleles that expanded to a full mutation (>200 repeats) in one generation contained 59 repeats; sequence analysis of the 59-repeat alleles from these two females revealed no AGG interruptions within the FMR1 CGG repeat. (2) When we corrected for ascertainment and recalculated the risks of expansion to a full mutation, we found that the risks for premutation alleles with <100 repeats were lower than those previously published. (3) When we examined the possible influence of sex of offspring on transmission of a full mutation-by analysis of 567 prenatal fragile X studies of 448 mothers with premutation and full-mutation alleles-we found no significant differences in the proportion of full-mutation alleles in male or female fetuses. (4) When we examined 136 transmissions of intermediate alleles from 92 mothers with no family history of fragile X, we found that, in contrast to the instability observed in families with fragile X, most (99/136 [72.8%]) transmissions of intermediate alleles were stable. The unstable transmissions (37/136 [27.2%]) in these families included both expansions and contractions in repeat size. The instability increased with the larger intermediate alleles (19% for 49-54 repeats, 30.9% for 55-59, and 80% for 60-65 repeats). These studies should allow improved risk assessments for genetic counseling of women with premutation or intermediate-size alleles.

X-chromosome inactivation is widely believed to be random in early female development and to result in a mosaic distribution of cells, approximately half with the paternally derived X chromosome inactive and half with the maternally derived X chromosome inactive. Significant departures from such a random pattern are hallmarks of a variety of clinical states, including being carriers for severe X-linked diseases or X-chromosome cytogenetic abnormalities. To evaluate the significance of skewed patterns of X inactivation, we examined patterns of X inactivation in a population of >1,000 phenotypically unaffected females. The data demonstrate that only a very small proportion of unaffected females show significantly skewed inactivation, especially during the neonatal period. By comparison with this data set, the degree of skewed inactivation in a given individual can now be quantified and evaluated for its potential clinical significance.

Purpose Three programmed death-1/programmed death-ligand 1 (PD-L1) inhibitors are currently approved for treatment of non-small-cell lung cancer (NSCLC). Treatment with pembrolizumab in NSCLC requires PD-L1 immunohistochemistry (IHC) testing. Nivolumab and atezolizumab are approved without PD-L1 testing, though US Food and Drug Administration-cleared complementary PD-L1 tests are available for both. PD-L1 IHC assays used to assess PD-L1 expression in patients treated with programmed death-1/PD-L1 inhibitors in clinical trials include PD-L1 IHC 28-8 pharmDx (28-8), PD-L1 IHC 22C3 pharmDx (22C3), Ventana PD-L1 SP142 (SP142), and Ventana PD-L1 SP263 (SP263). Differences in antibodies and IHC platforms have raised questions about comparability among these assays and their diagnostic use. This review provides practical information to help physicians and pathologists understand analytical features and comparability of various PD-L1 IHC assays and their diagnostic use. Methods We reviewed and summarized published or otherwise reported studies (January 2016 to January 2017) on clinical trial and laboratory-developed PD-L1 IHC assays (LDAs). Studies assessing the effect of diagnostic methods on PD-L1 expression levels were analyzed to address practical issues related to tissue samples used for testing. Results High concordance and interobserver reproducibility were observed with the 28-8, 22C3, and SP263 clinical trial assays for PD-L1 expression on tumor cell membranes, whereas lower PD-L1 expression was detected with SP142. Immune-cell PD-L1 expression was variable and interobserver concordance was poor. Inter- and intratumoral heterogeneity had variable effects on PD-L1 expression. Concordance among LDAs was variable. Conclusion High concordance among 28-8, 22C3, and SP263 when assessing PD-L1 expression on tumor cell membranes suggests possible interchangeability of their clinical use for NSCLC but not for assessment of PD-L1 expression on immune cells. Development of LDAs requires stringent standardization before their recommendation for routine clinical use.

Clinical evidence demonstrates that treatment with immune checkpoint inhibitor immunotherapy agents can have considerable benefit across multiple tumours. However, there is a need for the development of predictive biomarkers that identify patients who are most likely to respond to immunotherapy. Comprehensive characterisation of tumours using genomic, transcriptomic, and proteomic approaches continues to lead the way in advancing precision medicine. Genetic correlates of response to therapy have been known for some time, but recent clinical evidence has strengthened the significance of high tumour mutational burden (TMB) as a biomarker of response and hence a rational target for immunotherapy. Concordantly, immune checkpoint inhibitors have changed clinical practice for lung cancer and melanoma, which are tumour types with some of the highest mutational burdens. TMB is an implementable approach for molecular biology and/or pathology laboratories that provides a quantitative measure of the total number of mutations in tumour tissue of patients and can be assessed by whole genome, whole exome, or large targeted gene panel sequencing of biopsied material. Currently, TMB assessment is not standardised across research and clinical studies. As a biomarker that affects treatment decisions, it is essential to unify TMB assessment approaches to allow for reliable, comparable results across studies. When implementing TMB measurement assays, it is important to consider factors that may impact the method workflow, the results of the assay, and the interpretation of the data. Such factors include biopsy sample type, sample quality and quantity, genome coverage, sequencing platform, bioinformatic pipeline, and the definitions of the final threshold that determines high TMB. This review outlines the factors for adoption of TMB measurement into clinical practice, providing an understanding of TMB assay considerations throughout the sample journey, and suggests principles to effectively implement TMB assays in a clinical setting to aid and optimise treatment decisions.

The recent development of immune checkpoint inhibitors (ICIs) has led to promising advances in the treatment of patients with NSCLC and SCLC with advanced or metastatic disease. Most ICIs target programmed cell death protein 1 (PD-1) or programmed death ligand 1 (PD-L1) axis with the aim of restoring antitumor immunity. Multiple clinical trials for ICIs have evaluated a predictive value of PD-L1 protein expression in tumor cells and tumor-infiltrating immune cells (ICs) by immunohistochemistry (IHC), for which different assays with specific IHC platforms were applied. Of those, some PD-L1 IHC assays have been validated for the prescription of the corresponding agent for firstor second-line treatment. However, not all laboratories are equipped with the dedicated platforms, and many laboratories have set up in-house or laboratory-developed tests that are more affordable than the generally expensive clinical trialvalidated assays. Although PD-L1 IHC test is now deployed in most pathology laboratories, its appropriate implementation and interpretation are critical as a predictive biomarker and can be challenging owing to the multiple antibody clones and platforms or assays available and given the typically small size of samples provided. Because many articles have been published since the issue of the IASLC Atlas of PD-L1 Immunohistochemistry Testing in Lung Cancer, this review by the IASLC Pathology Committee provides updates on the indications of ICIs for lung cancer in 2019 and discusses important considerations on preanalytical, analytical, and postanalytical aspects of PD-L1 IHC testing, including specimen type, validation of assays, external quality assurance, and training.

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