Classification
Lung cancers are classified according to histological type. This classification has important implications for clinical management and prognosis of the disease. The vast majority of lung cancers are malignancies that arise from epithelial cells. Lung carcinomas are categorized by the size and appearance of the malignant cells seen by a histopathologist under a microscope. The two broad classes are non-small cell and small cell lung carcinoma.
There are three main sub-types: adenocarcinoma, squamous cell lung carcinoma, and large cell lung carcinoma.
Nearly 40% of lung cancers are adenocarcinoma. This type of cancer usually originates in peripheral lung tissue. Most cases of adenocarcinoma are associated with smoking; however, among people who have smoked fewer than 100 cigarettes in their lifetimes ("never-smokers"),adenocarcinoma is the most common form of lung cancer.] A subtype of adenocarcinoma, the bronchioloalveolar carcinoma, is more common in female never-smokers, and may have different responses to treatment.
Squamous cell carcinoma accounts for about 30% of lung cancers. They typically occur close to large airways. A hollow cavity and associated necrosis are commonly found at the center of the tumor.
About 9% of lung cancers are large cell carcinoma. These are so named because the cancer cells are large, with a lot of cytoplasm, large nuclei and conspicuous nucleoli.
Lung cancer staging
Lung cancer staging is an assessment of the degree of spread of the cancer from its original source. It is one of the factors affecting the prognosis and potential treatment of lung cancer.
The initial evaluation of non-small cell lung cancer staging uses the TNM classification. This based on the size of the primary tumor, lymph node involvement, and distant metastasis. After this, using the TNM descriptors, a group is assigned, ranging from occult cancer, through stage 0, IA (one-A), IB, IIA, IIB, IIIA, IIIB to IV (four). This stage group assists with the choice of treatment and estimate of prognosis.Small cell lung carcinoma has traditionally been classified as limited stage (confined to one half of the chest and within the scope of a single tolerable radiotherapy field) or extensive stage (more widespread disease). However the TNM classification and grouping are useful in estimating prognosis.
For both NSCLC and SCLC, there are two general types of staging evaluations: clinical staging and surgical staging. Clinical staging is performed prior to definitive surgery. It is based on the results of imaging studies (such as CT scans and PET scans) and biopsy results. Surgical staging is evaluated either intra- or post-operatively, and is based on the combined results of surgical and clinical findings, including surgical sampling of thoracic lymph nodes.
Prevention
Prevention is the most cost-effective means of mitigating lung cancer development. While in most countries industrial and domestic carcinogens have been identified and banned, tobacco smoking is still widespread. Eliminating tobacco smoking is a primary goal in the prevention of lung cancer, and smoking cessation is an important preventive tool in this process.
Policy interventions to decrease passive smoking in public areas such as restaurants and workplaces have become more common in many Western countries. Bhutan has had a complete smoking ban since 2005. India introduced a ban on smoking in public in October 2008.
The World Health Organization has called for governments to institute a total ban on tobacco advertising to prevent young people from taking up smoking. They assess that such bans have reduced tobacco consumption by 16% where instituted.
The long-term use of supplemental vitamin A, vitamin C, vitamin D or vitamin Edoes not reduce the risk of lung cancer. Some studies suggest that people who eat diets with a higher proportion of vegetables and fruit tend have a lower risk. However this is likely due to confounding. More rigorous studies have not demonstrated a clear association.