What is Lung Cancer?
Cancer of the lung, like all cancers, results from an abnormality in the body’s basic unit of life, the cell. Normally, the body maintains a system of checks and balances on cell growth so that cells divide to produce new cells only when needed. Disruption of this system of checks and balances on cell growth results in an uncontrolled division and proliferation of cells that eventually forms a mass known as a tumor.
Tumors can be benign or malignant; when we speak of “cancer,” we refer to those tumors that are considered malignant. Benign tumors can usually be removed and do not spread to other parts of the body. Malignant tumors, on the other hand, grow aggressively and invade other tissues of the body, allowing entry of tumor cells into the bloodstream or lymphatic system and then to other sites in the body. This process of spread is termed metastasis; the areas of tumor growth at these distant sites are called metastases. Since lung cancer tends to spread or metastasize very early in its course, it is a very life-threatening cancer and one of the most difficult cancers to treat. While lung cancer can spread to any organ in the body, certain organs — particularly the adrenal glands, liver, brain, and bone — are the most common sites for lung-cancer metastasis.
The lung is also a very common site for metastasis from tumors in other parts of the body. Tumor metastases are made up of the same type of cells as the original, or primary, tumor. For example, if prostate cancer spreads via the bloodstream to the lungs, it is metastatic prostate cancer in the lung and is not lung cancer.
Types of Lung Cancer
Lung cancers, also known as bronchogenic carcinomas (carcinoma is another term for cancer), are broadly classified into two types: small cell lung cancers (SCLC) and non-small cell lung cancers (NSCLC). This classification is based upon the microscopic appearance of the tumor cells themselves. These two types of cancers grow and spread in different ways and may have different treatment options, so a distinction between these two types is important.
SCLC comprise about 20% of lung cancers and are the most aggressive and rapidly growing of all lung cancers. SCLC are strongly related to cigarette smoking, with only 1% of these tumors occurring in nonsmokers. SCLC metastasize rapidly to many sites within the body and are most often discovered after they have spread extensively. Referring to a specific cell appearance often seen when examining samples of SCLC under the microscope, these cancers are sometimes called oat cell carcinomas.
NSCLC are the most common lung cancers, accounting for about 80% of all lung cancers. NSCLC can be divided into three main types that are named based upon the type of cells found in the tumor:
Adenocarcinomas are the most commonly seen type of NSCLC in the U.S. and comprise up to 50% of NSCLC . While adenocarcinomas are associated with smoking like other lung cancers, this type is observed as well in nonsmokers who develop lung cancer. Most adenocarcinomas arise in the outer, or peripheral, areas of the lungs. Bronchioloalveolar carcinoma is a subtype of adenocarcinoma that frequently develops at multiple sites in the lungs and spreads along the preexisting alveolar walls.
Squamous cell carcinomas were formerly more common than adenocarcinomas; at present, they account for about 30% of NSCLC. Also known as epidermoid carcinomas, squamous cell cancers arise most frequently in the central chest area in the bronchi.
Large cell carcinomas, sometimes referred to as undifferentiated carcinomas, are the least common type of NSCLC.
Mixtures of different types of NSCLC are also seen.
Other types of cancers can arise in the lung; these types are much less common than NSCLC and SCLC and together comprise only 5%-10% of lung cancers:
Bronchial carcinoids account for up to 5% of lung cancers. These tumors are generally small (3-4 cm or less) when diagnosed and occur most commonly in people under 40 years of age. Unrelated to cigarette smoking, carcinoid tumors can metastasize, and a small proportion of these tumors secrete hormone-like substances that may cause specific symptoms related to the hormone being produced. Carcinoids generally grow and spread more slowly than bronchogenic cancers, and many are detected early enough to be amenable to surgical resection.
Cancers of supporting lung tissue such as smooth muscle, blood vessels, or cells involved in the immune response can rarely occur in the lung.
As discussed mentioned, metastatic cancers from other primary tumors in the body are often found in the lung. Tumors from anywhere in the body may spread to the lungs either through the bloodstream, through the lymphatic system, or directly from nearby organs. Metastatic tumors are most often multiple, scattered throughout the lung, and concentrated in the peripheral rather than central areas of the lung.
Advanced Lung Cancer Articles*
Revision Of Lung Cancer Staging System
A revised staging system, called IASLC Staging System, for non-small cell lung cancer patients has been developed by the American College of Chest Physicians. The revised staging system provides a detailed common nomenclature and clearly helps to predict how severe the lung cancer is for patients with non-small cell lung cancer through the addition and reclassification of many new patient subgroups. This revised system provides a more scientific approach to lung cancer. The previous system was known as TNM staging system. “The IASLC classification system is designed to name and define prognosis. The new IASLC staging system was accepted by the AJCC and UICC and will appear in the UICC staging manual in November of 2009.
FDA Approves First Maintenance Drug Therapy For Advanced Lung Cancer
The FDA has approved the drug Alimta, which will be used for therapy of metastatic lung cancer. Alimta is a drug produced by Eli Lilly and Company. Alimta disrupts metabolic processes that depend on B-vitamin folate, which provided cell replication and duplication. This drug will be used for non-small cell lung cancer. A case study was conducted in which participants that received the drug Alimta survived 5.2 months more than participants that received a placebo, or inactive substance. Alimta was first approved in 2004 to treat patients with mesothelioma, a cancer that is caused by asbestos exposure. The drug was later approved in 2009 to treat patients with non-small cell lung cancer whose disease worsened prior to chemotherapy drugs.
Compugen Announces Discovery Of Blood Based Biomarker For Diagnosis Of Lung Cancer
Compugen Limited announced the discovery of CGEN-438. CGEN-438 can be used to serve as both a serum biomarker for the diagnosis of small cell lung cancer and as a component in a biomarker combination for the diagnosis of non-small cell lung cancer patients. Blood levels of the peptide was measured in about 40 lung cancer patients and studied were conducted to conclude that serum samples of small cell lung cancer patients were higher than those detected in healthy patients. In other words, it can be used as a diagnostic biomarker for small cell lung cancer. CGEN-438 can provide us with information by acting as a biomarker about whether or not a patient has small cell lung cancer.
New Genetic Techniques To Combat Lung Cancer
New results on genetic techniques to treat lung cancer were released at the 1st European Lung Cancer Conference. Israeli researchers from Rosetta Genomics discovered a test to differentiate between different types of lung cancers. In addition, these Israeli researchers also discovered that based on different levels of microRNA molecules in tissue samples, they are able to distinguish each type of lung cancer. In another type of research, a group of Italian researchers test included the gene LCK, which marks immune cell anticancer activity, DUSP-6 which regulates a signaling pathway involved in cancer spread, and ERCC1, which is a significant therapeutic biomarker in non small cell lung cancer. This researcher can help oncologists with a more efficient use of adjuvant drug after lung surgery.
* These articles identified and condensed by Pratik Patel a high school Summer intern. Reviewed and approved by our medical board 11/1/2009.