How does smoking cause cancer
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How Smoking Causes Cancer
Introduction to Smoking and Cancer Risk
Smoking is a leading cause of cancer, responsible for a significant percentage of cancer-related deaths worldwide. The relationship between smoking and cancer is well-documented, with numerous studies highlighting the various mechanisms through which tobacco smoke induces carcinogenesis.
Carcinogens in Tobacco Smoke
Tobacco smoke contains over 60 known carcinogens, including polycyclic aromatic hydrocarbons and tobacco-specific nitrosamines, which are particularly potent in causing lung cancer . These carcinogens interact with DNA, leading to mutations that can initiate and promote tumor development.
Mechanisms of DNA Damage
The carcinogens in tobacco smoke cause direct DNA damage, leading to mutations. One of the primary mechanisms involves the misreplication of DNA damage caused by these carcinogens, resulting in a high mutation burden in the affected tissues. Additionally, tobacco smoke can activate DNA editing enzymes like APOBEC cytidine deaminases, further increasing the mutation load.
Histological Types of Lung Cancer
Different types of lung cancer are associated with smoking, with varying degrees of risk. Squamous cell carcinoma (SqCC) and small cell lung cancer (SCLC) show higher odds ratios (ORs) for smokers compared to adenocarcinoma (AdCa). For instance, current male smokers with a high daily cigarette intake have ORs of 103.5 for SqCC and 111.3 for SCLC, compared to 21.9 for AdCa.
Inflammation and Tumor Promotion
Chronic exposure to tobacco smoke not only initiates cancer but also promotes tumor growth through inflammation. Tobacco smoke induces inflammation, which enhances cell proliferation and tumor development, particularly in lung epithelial cells. This inflammatory response is mediated by pathways involving IKKbeta and JNK1, which are crucial for tumor promotion.
Broader Impact on Various Cancers
Smoking is not limited to causing lung cancer; it is also a major risk factor for cancers of the larynx, oral cavity, pharynx, esophagus, pancreas, kidney, and bladder . The risk of these cancers increases with the duration and intensity of smoking, and smoking cessation can significantly reduce this risk, although it may not return to baseline levels even after many years .
Global and Gender Differences
The impact of smoking on cancer varies globally and between genders. In developed countries, smoking accounts for a higher percentage of cancer cases compared to developing countries. Men have historically shown higher rates of smoking-related cancers, but the incidence in women is rising, indicating a potential future epidemic .
Conclusion
Smoking is a major preventable cause of cancer, with a well-established link to multiple cancer types. The carcinogens in tobacco smoke cause direct DNA damage, leading to mutations and cancer initiation. Chronic exposure also promotes tumor growth through inflammation. Reducing smoking prevalence is crucial for decreasing the global cancer burden.
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