Recent discovery of mutations in the tyrosine kinase domain of the epidermal growth factor receptor (EGFR) gene in lung adenocarcinoma greatly stimulated biomarker research on predictive factors for ...EGFR tyrosine kinase inhibitors (TKI), such as gefitinib and erlotinib. Although patients with activating mutations of the EGFR generally respond to EGFR TKIs very well, it is natural to assume that there is no sole determinant, considering great complexity and redundancy of the EGFR pathway. Subsequently, roles of different types of EGFR mutations or mutations of genes that are members of the EGFR pathway such as KRAS and HER2 have been evaluated. In this review, we summarize the recent findings about how mutations of the EGFR and related genes affect sensitivity to EFGR‐TKIs. We also discuss molecular mechanisms of acquired resistance to EGFR‐TKIs that is almost inevitable in EGFR‐TKI therapy. The door for genotype‐based treatment of lung cancer is beginning to open, and through these efforts, it will be possible to slow the progression of lung cancer and eventually, to decrease mortality from lung cancer. (Cancer Sci 2007; 98: 1817–1824)
Considerable knowledge has accumulated about mutations of the epidermal growth factor receptor (EGFR)-tyrosine kinase domain since these were first identified in 2004. Patients with nonsmall cell ...lung cancer with this mutation show dramatic clinical responses to treatment with EGFR-tyrosine kinase inhibitors, whose effectiveness has been established recently in large clinical trials. Most of the mechanisms responsible for resistance to treatment, which most responders experience eventually, have been elucidated, and methods to overcome resistance have been developed. In addition to the clinical benefit, understanding EGFR mutations sheds new light on the molecular and pathological aspects of this adenocarcinoma subset, which include frequent development in nonsmokers or females, and particular clusters within the molecular classification in lung cancer. In contrast to the involvement of EGFR mutations in the early stage of lung adenocarcinoma development, EGFR amplification is superimposed on the progression to invasive cancer. In this review, I summarize the clinicopathological characteristics of EGFR mutations in lung cancer. I also provide an overview of the current understanding of the lung adenocarcinoma subset harboring EGFR mutations with special reference to the molecular classification of lung cancer and the novel concept of the “terminal respiratory unit.”
Epidermal growth factor receptor (EGFR) and its three related proteins (the ERBB family) are receptor tyrosine kinases that play essential roles in both normal physiological conditions and cancerous ...conditions. Upon binding its ligands, dynamic conformational changes occur in both extracellular and intracellular domains of the receptor tyrosine kinases, resulting in the transphosphorylation of tyrosine residues in the C-terminal regulatory domain. These provide docking sites for downstream molecules and lead to the evasion of apoptosis, to proliferation, to invasion and to metastases, all of which are important for the cancer phenotype. Mutation in the tyrosine kinase domain of the EGFR gene was found in a subset of lung cancers in 2002. Lung cancers with an EGFR mutation are highly sensitive to EGFR tyrosine kinase inhibitors, such as gefitinib and erlotinib. Here, we review the discovery of EGFR, the EGFR signal transduction pathway and mutations of the EGFR gene in lung cancers and glioblastomas. The biological significance of such mutations and their relationship with other activated genes in lung cancers are also discussed.
In April 2021, after a five-year interval, the WHO revised the classification system for thoracic tumors. Although there were no major changes in this revision, the information has been updated in ...detail, and several new diseases have been introduced. In addition, the new format of "Essential and desirable diagnostic criteria" is used throughout the text, which is designed to facilitate the diagnosis and understanding of diseases. This review summarizes the changes made in the 5th edition of the WHO classification of thoracic tumors.
Some studies have shown that epidermal growth factor receptor (EGFR) mutations can be heterogeneously distributed in individual tumors. In this study, we re-evaluated the distribution of EGFR ...mutations within tumors.
We used multiple approaches, including an analysis of simultaneous dual hot spot mutations, a trans-sectional analysis of individual lung adenocarcinomas, and comparisons of the mutation patterns between primary and metastatic sites and between primary and recurrent tumors.
None of the 862 tumors harboring an EGFR mutation showed simultaneous dual hot spot mutations, although identical EGFR mutations were found throughout individual tumors in a trans-sectional analysis involving 50 tumors divided into three parts and five lung adenocarcinomas divided into 100 parts. In addition, no discordant mutation patterns were detected among 77 paired primary and metastatic site samples or among 54 primary and recurrent tumor pairs.
All of these results suggest that the heterogeneous distribution of EGFR mutations is extremely rare. However, it is possible that pseudoheterogeneity occurs because of a combination of mutant allele-specific imbalance and heterogeneously distributed EGFR amplification, especially when a less sensitive method is used for detection. Specifically, when EGFR amplification occurs, the mutant allele is amplified, and this amplification is involved in invasive growth. Accordingly, invasive growth area significantly over-represents the mutation signal. In contrast, weak EGFR mutation signals in the area without EGFR amplification may not reach the threshold of detection because of the mixture with normal cells. Such unbalanced mutation signals might lead to pseudoheterogeneity.
The 2021 WHO Classification of Thoracic Tumours was published earlier this year, with classification of lung tumors being one of the chapters. The principles remain those of using morphology first, ...supported by immunohistochemistry, and then molecular techniques. In 2015, there was particular emphasis on using immunohistochemistry to make classification more accurate. In 2021, there is greater emphasis throughout the book on advances in molecular pathology across all tumor types. Major features within this edition are (1) broader emphasis on genetic testing than in the 2015 WHO Classification; (2) a section entirely dedicated to the classification of small diagnostic samples; (3) continued recommendation to document percentages of histologic patterns in invasive nonmucinous adenocarcinomas, with utilization of these features to apply a formal grading system, and using only invasive size for T-factor size determination in part lepidic nonmucinous lung adenocarcinomas as recommended by the eighth edition TNM classification; (4) recognition of spread through airspaces as a histologic feature with prognostic significance; (5) moving lymphoepithelial carcinoma to squamous cell carcinomas; (6) update on evolving concepts in lung neuroendocrine neoplasm classification; (7) recognition of bronchiolar adenoma/ciliated muconodular papillary tumor as a new entity within the adenoma subgroup; (8) recognition of thoracic SMARCA4-deficient undifferentiated tumor; and (9) inclusion of essential and desirable diagnostic criteria for each tumor.
Anaplastic lymphoma kinase (ALK) rearrangement-positive non-small-cell lung cancers can be effectively treated with an ALK tyrosine kinase inhibitor (TKI) such as crizotinib, but the response ...magnitude and duration are heterogeneous. Several ALK variants have been identified, but few studies have focused on the effects of different ALK variants on the efficacy of crizotinib.
Among 55 patients treated with crizotinib as the initial ALK-TKI between January 2007 and December 2014, we identified 35 patients with tumor specimens that could be evaluated for ALK variants by reverse transcription polymerase chain reaction. We retrospectively evaluated the efficacy of crizotinib on the basis of the objective response rate and progression-free survival (PFS) according to the ALK variants.
The most frequent ALK variant was variant 1 in 19 patients (54%), followed by variant 2 in five patients (14%), variant 3a/3b in four patients (12%), and other variants in seven patients (20%). Objective response rate was 69% in all patients, whereas it was 74% and 63% in the variant 1 and non-variant 1 groups, respectively. The median PFS time was significantly longer in patients with variant 1 than in those with non-variant 1 (median PFS, 11.0 months 95% CI, 6.5 to 43.0 months v 4.2 months 95% CI, 1.6 to 10.2 months, respectively; P < .05). Multivariable analysis identified two significant factors associated with PFS duration, ALK variant 1 (hazard ratio, 0.350; 95% CI, 0.128 to 0.929; P < .05) and advanced stage (hazard ratio, 4.646; 95% CI, 1.381 to 21.750; P < .05).
Our results indicate the better efficacy of crizotinib in patients with ALK variant 1 versus non-variant 1. The ALK variant status might affect the efficacy of ALK-TKIs.
The new grading system proposed by the Pathology Committee of the International Association for the Study of Lung Cancer in 2020 was based on the combination of the histologically predominant subtype ...and high-grade component. Because the predominant subtypes are associated with characteristic subsets, unique subsets can be identified by this grading system.
We analyzed the clinicopathologic, genotypic, and prognostic features of a cohort of 781 consecutive patients with invasive nonmucinous adenocarcinoma of the lung.
Grade 3 tumors were associated with younger age, male sex, a higher smoking dose, and aggressive features (tumor size, lymph node metastasis, stage, lymphovascular invasion, and pleural invasion). Recurrence-free survival and 3-year overall survival were well-stratified according to tumor grade, and the differences were confirmed with multivariate analysis using the Cox proportional hazard model. Radiologically, most grade 3 tumors exhibit a solid nodular pattern on computed tomography images and a high maximum standardized uptake value with positron emission tomography. Genotypically, 43% of the grade 3 adenocarcinomas lacked any driver mutations, although one of the driver mutations was detected in 79% of grade 1 or 2 tumors. Patient age, positive smoking history, solid nodule on computed tomography image, and higher maximum standardized uptake value were identified as significant preoperative predictive factors of grade 3 tumors, with a prediction rate greater than 90%.
Besides stratifying the patient outcomes, the new grading system characterized unique clinicopathologic subsets and this study suggested that grade 3 tumors could be predicted using the preoperative variables.
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