Key Event Title
|Level of Biological Organization|
Key Event Components
Key Event Overview
AOPs Including This Key Event
|AOP Name||Role of event in AOP|
|Ionizing energy leading to lung cancer||AdverseOutcome|
|All life stages||High|
Key Event Description
Abnormally high levels of cell proliferation in the lungs may eventually culminate in the formation of malignant tumours and thus lung cancer. The term lung cancer refers to all malignant neoplasms arising from the bronchial, bronchiolar, and alveolar epithelium (Keshamouni et al., 2009). The cellular origin(s) of lung cancer remains largely unknown. It has been speculated that different tumour histopathological subtypes arise from distinct cells of origin localized in defined microenvironments. Histological characteristics of lung cancers, as defined by light microscopy, have led to the categorization of lung cancers into four main subtypes: small cell carcinoma, adenocarcinoma, squamous cell carcinoma, and large cell carcinoma (Beasly et al., 2005). These histological subtypes are grouped under one of the two umbrella terms used to describe lung cancers: small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC). The term SCLC refers to small cell carcinoma. The term NSCLC, which represents approximately 85% of all lung cancers (Molina et al., 2008), encompasses squamous cell carcinoma, adenocarcinoma, and large cell carcinoma. These three tumour types are grouped together due to similarities in their prognosis and management (Keshamouni et al., 2009); patients with NSCLC often have poor prognoses and low 5-year survival rates due to the high metastatic potential of the tumours (Spira and Ettinger, 2004; Herbst et al., 2008). Some of the most common sites for lung cancer metastasis are the other lobe of the lungs, skeleton, adrenal glands, liver, and brain (Simon et al., 2015).
How It Is Measured or Detected
|Assay Name||Reference||Description||OECD Approved Assay|
|Computed Tomography (CT) Scans: CT, High-Resolution CT (HRCT), and Positron Emission Tomography-CT (PET-CT)||Bach et al., 2012; Ollier et al., 2014||CT scans are described as a 3D X-ray; They provide cross-sections of organs/tissues/bones, and can thus be used to detect tumours||N/A|
|Magnetic Resonance Imaging (MRI)||Khalil et al., 2016; Wu et al., 2011||This technique uses magnetic fields and radio waves (NOT ionizing radiation) to generate a picture of organs, and can thus be used to detect tumours||N/A|
|Sputum Analysis||Hubers et al., 2013||Sputum is collected and analyzed for a variety of markers, including mutations in KRAS and TP53, specific RNA/protein biomarkers, and chromosomal aberrations||N/A|
|Bronchoscopy: Conventional White Light Bronchoscopy, Autofluorescence Bronchoscopy (AFB), and Endobronchial Ultrasonography (EBUS)||Ikeda et al., 2007||Bronchoscope (usually with a camera) is passed down through the throat to the lungs to provide a visual of the respiratory tract; Traditionally, visualization has been performed using conventional white light, but new technologies have also allowed for visualization using fluorescence and ultrasound technologies||N/A|
|Transbronchial Needle Aspiration||Navani et al., 2015; Aziz, 2012||A needle is used to aspirate a tissue sample from a lesion of suspected lung cancer for analysis||N/A|
|Analysis of Volatile Organic Compounds in the Breath||Zhou et al., 2017||Volatile organic compounds, which may act as lung cancer biomarkers, are collected from the breath and quantified (mostly using mass spectrometry)||N/A|
|Cell Transformation Assays||Redpath et al., 1987||Measurement of the tumourigenicity of a tumour/biopsy sample by analyzing changes in cell physiology and morphology in response to tumour-inducing radiation or chemicals||Yes (No. 231)|
Rodent Two-Year Cancer Bioassays
|Matsumo, 2012; Nambiar, 2014; Maronpot, 2015||Animals are exposed to a possible carcinogen for a long period of time (often two years), allowing for long-term cancer-related studies||Yes (No. 451)|
|Window Chamber Models||Moeller, 2004; Schafer, 2014; Chen, 2016||Window chambers are implanted into the animal to observe tumour progression in living animals using imaging techniques such as in vivo microscopy, MRI or nuclear imaging||N/A|
|Xenograft Assays||Wang, 2018; Shi, 2017; Jin, 2018; Wang, 2017; Zhou, 2012||Tumour cells (usually human) are grown in vitro and injected into animals to induce tumour growth and/or to test the tumourigenicity of the injected cells||N/A|
Domain of Applicability
Lung cancer and subsequent metastasis occurs in multicellular eukaryotic vertebrate organisms that have lungs.
Evidence for Perturbation by Stressor
Regulatory Significance of the Adverse Outcome
At present the AOP framework is not readily used to support regulatory decision-making in radiation protection practices.The goal of developing this AOP is to bring attention to the framework as an effective means to organize knowledge and identify gaps associated with the mechanistic understanding of low dose radiation exposures. We have used lung cancer as the case example due to its relevance to both radiation and chemical risk assessment. This AOP will help build the concept of an “all hazards” approach to risk assessment, as it will be the first with a molecular initiating event that is specific to a radiation insult. This in turn could serve to identify networks that are critical to both radiation and chemical exposure scenarios and contribute to prioritizing co-exposures of relevance to risk assessment. By developing this AOP, we will support the necessary efforts highlighted by the international and national radiation protection agencies such as, the United Nations Scientific Committee on the Effects of Atomic Radiation, International Commission of Radiological Protection, International Dose Effect Alliance and the Electric Power Research Institute Radiation Program to consolidate and enhance the knowledge in understanding the mechanisms of low dose radiation exposures from the cellular to organelle levels within the system.
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Bach, P. B. et al. (2012), “Benefits and harms of CT screening for lung cancer: a systematic review”, JAMA, 307(22), 2418-2429. doi:10.1001/jama.2012.5521
Beasley, M. B., Brambilla, E., & Travis, W. D. (2005), “The 2004 World Health Organization classification of lung tumors”, Seminars in Roentgenology, 40(2), 90-97. doi:10.1053/j.ro.2005.01.001
Chen Y, Maeda A, Bu J, DaCosta R. (2016), “Femur Window Chamber Model for In Vivo Cell Tracking in the Murine Bone Marrow”, J Vis Exp. (113). doi: 10.3791/54205.
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Ikeda, N. et al. (2007), “Comprehensive diagnostic bronchoscopy of central type early stage lung cancer”, Lung Cancer, 56(3), 295-302. doi:10.1016/j.lungcan.2007.01.009
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Maronpot RR, Thoolen RJ, Hansen B. (2015), “Two-year carcinogenicity study of acrylamide in Wistar Han rats with in utero exposure”,Exp Toxicol Pathol. 67(2):189-95. doi: 10.1016/j.etp.2014.11.009.
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