Lung cancer

Lung cancer

Lung cancer

Definition

This is primary lung malignancy that arises from the lung tissue. There are several types of primary cancer of the lung including squamous cell carcinoma, adenocarcinoma, small cell carcinoma, and large cell carcinoma. Here are some of the listed types

Adenocarcinomas: These types of cancers are common in North America and Japan. They tend to occur among smokers, although nonsmokers are more likely to develop adenocarcinoma than other lung cancer types. On radiological examination, they are found more peripherally, but can occur almost anywhere, and can be multifocal. They have been known to fill the entire lobe of the lung tissue. Other x-ray findings show that they are associated with solid opacities, ground-glass opacities, or mixed patterns. Epidemiologically, Adenocarcinomas represent 35%-40% of lung carcinomas. The variants of adenocarcinomas include types such as signet ring, clear cell, mucinous, and fetal adenocarcinomas

Squamous cell (Epidermoid): This type of cancer tends to occur centrally and is highly associated a history of smoking. It’s a malignancy that shows squamous differentiation 20% to 30% of lung cancers. It spreads by locally invading the surrounding tissues and forms cavities in the lungs. The differential diagnosis includes reactive processes that may result in squamous metaplasia with reactive atypia as seen during infections or radiation-induced injury

Small cell carcinoma (Oat cell): Small cell carcinomas are poorly differentiated neuroendocrine tumors that tend to occur centrally. Smoking is a risk factor in many of these types of cancers. There is a high cavitation rate in people with this type of cancer. About 20% of lung carcinomas consist of small cell carcinomas. They tend to spread through the lymphatic ducts. Some genetic information available indicates that the small cell carcinomas are associated with lesions of the short arm of chromosome 3.

Large cell carcinoma: These types of cancers consist of fewer than 10% of lung carcinomas. They tend to occur peripherally, and are defined as poorly differentiated carcinomas of the lung. On microscopic examination, they are composed of larger malignant cells with no squamous, glandular differentiation, or features of small cell carcinoma. They occur in sheets of large malignant cells, with cell death (necrosis). They can spread to the brain (CNS) and mediastinum. They have a rapid growth rate with early spread (metastasis)

Large Cell Neuroendocrine Carcinoma (LCNEC): This type of cancer is a subtype of large cell carcinoma that shows neuroendocrine differentiation as seen on light microscopy. It accounts for approximately 3% of lung cancers. LCNEC may be difficult to diagnose on microscopic examination (cytologically) and has been know to be difficult to differentiate from a small cell carcinoma. The main cytologic features include groups of cells with peripheral rosette formation, nuclear molding, or immunohistochemical staining with neuroendocrine markers. Those with this type of cancer show a prognosis that is intermediate between other non-small cell carcinomas and small cell carcinoma.

Typical Carcinoid Tumor: The carcinoid tumors are low-grade neuroendocrine tumors that on microscopic examination show tumor cells arranged in organoid nests, trabeculae, or spindled patterns.  The tumors do not have necrosis at the center and have no significant mitotic activity. These types of tumors are common in nonsmokers. The have been known to be associated with lesion in the inside of the bronchus but can occur more peripherally. Their prognosis is good. A carcinoid tumorlet is measurs less than 5 mm in diameter.

Epidemiology

  • Lung cancer is responsible for >30% of cancer deaths in males and >25% of cancer deaths in females. It has been the most common cancer in the world since 1985 and is the leading cause of cancer-related death.
  • Tobacco smoking is implicated in 85% of cases; second-hand smoke is responsible for approximately 20% of cases.
  • There are >180,000 new cases of lung cancer yearly in the U.S., most occurring >age 50 yr (<4% in patients <40 yr of age).
  • Among women there has been a 600% increase in incidence of lung cancer during the past 80 years. The rates of death among women with lung cancer in the U.S. are the highest in the world.

What causes lung cancer?

  1. Smoking: It has been established that up to 90% of cases of lung cancer are related to smoking cigarettes. Studies also show that passive smoking is also a risk factor for lung cancer.
  2. Majority of Lung cancers in non-smokers are usually adenocarcinomas.
  3. Environmental agents such as radon; industrial agents such as ionizing radiation, asbestos, nickel, uranium, vinyl chloride, chromium, arsenic, coal dust are common culprits in the etiology of lung cancer. Exposure to these agents over a period of time can lead to cancer of the lungs.
  4. Asbestos: Long term exposure to asbestos, especially those in building industry has been shown to cause lung cancer. About 10% of lung cancers are caused by exposure to asbestos. A smoker exposed to asbestos has an almost 100-fold risk of lung cancer compared with a non-exposed nonsmoker.

Where the cancer spreads to

Dissemination (spread of cancer) to various regions has been noted in association with lung cancers. The following are some of the areas where metastatic spread has been noted:

  1. Dissemination to extra thoracic sites ( outside the chest)
    • The brain
    • Bones
    • Liver
    • Adrenal glands.
  2. Local and regional dissemination
    • The cancer can spread to the neighboring lobe of the same lung, or to the other lung
    • Spread to the hilar, mediastinal, clavicular or axillary lymph nodes
    • Direct spread to the mediastinum, blood vessels of the chest wall, pericardium, pleura, vertebrae or ribs, and brachial plexus.
  3. Small cell lung carcinoma has been shown to spread at a very early stage to both local and extra thoracic sites. The primary form of treatment is chemotherapy

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