In general, lung cancer is strongly correlated with smoking tobacco. In both HIV-infected and non-infected patients, lung cancer predominately affects smokers. In fact, researchers estimate that about 90% of lung cancer cases are caused by smoking. This is because tobacco smoke contains over 4,000 chemical compounds, many of which have been shown to be carcinogenic (cancer-causing). In addition, recent research suggests that the human chromosome number 6 is likely to contain a gene that confers an increased vulnerability to the development of lung cancer in smokers.
The risk of lung cancer is "substantially elevated" among HIV-infected patients, according to a cohort study conducted by researchers at the National Cancer Institute. The researchers reported an incidence of 170 per 100,000 HIV patients. Also, HIV patients who smoke have an even greater risk of developing lung cancer. The researchers reported that 85% of the patients who developed lung cancer were smokers. According to the researchers, the incidence of lung cancer was unrelated to HIV-induced immunosuppression.
There are several theories that aim to explain the prevalence of lung cancer among HIV patients. Some researchers believe that low numbers of natural killer cells (white blood cells that attack and kill tumor cells or microbial cells) may lead to the growth of abnormal cells or that HIV may stimulate abnormal growth factors.
Certain lung diseases, especially chronic obstructive pulmonary disease (COPD), are associated with a slightly increased risk (four to six times the risk of a non-smoker) for the development of lung cancer.
Lung cancer survivors are also more likely to develop lung cancer than the general population. Survivors of non-small cell lung cancers have an increased risk of about 1-2% per year for developing lung cancer a second time. Small cell lung cancer survivors have an increased risk of nearly 6% of developing lung cancer a second time.
Exposure to air pollution can increase the risk of developing lung cancer. Up to one percent of lung cancer deaths can be attributed to breathing polluted air.
Small cell and non-small cell cancers generally cause similar symptoms, including cough, shortness of breath, bloody sputum, loss of appetite, weight loss, chest pain, and wheezing or pneumonia. Adenocarcinoma may also cause chest pain with breathing.
If the cancer has metastasized (spread) to other parts of the body, symptoms may include hoarseness of the voice, difficulty swallowing, headaches, enlarged lymph nodes, pain or discomfort under the ribs, weakness, numbness, paralysis, bone or abdominal pain, or swelling of the face, arms, and neck.
In addition, many nonspecific symptoms are also seen in lung cancer patients, including weight loss, weakness, depression, mood changes, and fatigue.
General: If lung cancer is suspected, imaging studies or a bronchoscopy is performed to determine if there is a tumor in the lungs. If there is abnormal tissue growth in the lungs, a biopsy of the tumor is performed to confirm a diagnosis.
Chest X-ray: If lung cancer is suspected, a chest X-ray is usually the first diagnostic test that is conducted. Chest X-rays may help the physician detect abnormal tissue growth in the lungs. The healthcare provider may observe calcified nodules or tumors. However, X-rays cannot determine whether these areas are cancerous or not.
Computerized tomography (CT) scan: A computerized tomography (CT) scan may be performed on the chest, abdomen, and/or brain to look for both metastatic and primary tumors. The test is often performed when X-rays are negative or do not yield sufficient information about the extent or location of a tumor. CT scans are X-ray procedures that combine multiple images with the aid of a computer to generate cross-sectional views of the body. CT scans are more sensitive than standard chest X-rays in the detection of lung nodules. Sometimes intravenous (injected into the vein) contrast material is administered before the procedure to help identify the organs and their positions. According to scientific studies, CT scans used to detect lung cancer generally have a sensitivity ranging from 70-90% and a specificity ranging from 60-90%.
Magnetic resonance imaging (MRI) scan: Magnetic resonance imaging (MRI) scans may be conducted to determine the precise location of the tumor. MRI images are detailed and can detect tiny changes of structures within the body. A substance called gadolinium (chemical substance) is injected into the patient through a vein in order to provide detailed images of the lungs. The gadolinium clumps around the cancer cells so they show up brighter in the picture. People with heart pacemakers, metal implants, artificial heart valves, and other surgically implanted structures cannot be scanned with an MRI because of the risk that the magnet may move the metal parts of these structures.
Positron emission tomography
(PET): During a positron emission tomography (PET) test, a small amount of radionuclide glucose (sugar) is injected into a vein to help make the tissues and organs more visible. The PET scanner rotates around the body and takes a picture of where glucose is being used in the body. Malignant tumor cells appear brighter in the image because they are more active and consume more glucose than normal cells. Sensitivities up to 95% and specificities up to 86% have been reported with PETs.
Bone scans: Once lung cancer has been diagnosed, a qualified healthcare professional may conduct a bone scan to determine whether the cancer has metastasized to the bones. During the procedure, a small amount of radioactive material is injected into the bloodstream. The bone scan can detect abnormal areas in the bones because the radioactive substance collects in areas that contain metastatic tumors.
Sputum cytology: A sputum cytology test is the least invasive diagnostic test, but it is limited because tumor cells are not always present in the sputum. Also, non-cancerous cells occasionally undergo changes in reaction to inflammation or injury and they may be mistaken for cancer cells. During the procedure, the patient coughs hard, expelling material from the lungs into a culture. The sputum sample is then analyzed in a laboratory for cancerous cells.
Bronchoscopy: During a bronchoscopy, a thin, flexible tube with a camera (bronchoscope) is inserted through the mouth, into the esophagus. The test allows the healthcare provider to look inside the lungs for tumors. If a tumor is seen, a tissue sample can be taken and analyzed in the lab to confirm a diagnosis. This procedure is generally accurate when the tissue from the affected area is adequately sampled. However, sometimes, uninvolved areas of the lung are mistakenly sampled, which may cause a false negative test result. The procedure can be uncomfortable and requires sedation or anesthesia.
Needle biopsy: Fine needle aspiration (FNA) through the skin, usually performed with radiological imaging for guidance, may be performed to retrieve a tissue sample from tumor nodules in the lungs. Needle biopsies are especially useful when the tumor is peripherally located in the lung and not accessible to sampling by bronchoscopy. During the procedure, a local anesthetic is administered before the thin needle is inserted through the chest wall into the abnormal area in the lung. Cells are suctioned into the syringe and are examined under the microscope for cancerous cells. This procedure is generally accurate when performed correctly. However, in some cases, uninvolved areas of the lung may be sampled by mistake. If a sample is taken from an unaffected area, the results may be false negative.
Thoracentesis: Sometimes lung cancers involve the lining tissue of the lungs (pleura), which can lead to an accumulation of fluid in the space between the lungs and chest wall (called a pleural effusion). Aspiration of a sample of this fluid with a thin needle (thoracentesis) may reveal the cancer cells and establish the diagnosis.
Surgical tests: If lung cancer is suspected, but all other diagnostic methods produce negative results, surgical methods may be considered. During a mediastinoscopy, a probe is surgically inserted to collect a tissue sample of the tumor mass in the chest cavity between the lungs. During a thoracotomy, the chest wall is surgically opened and the surgeon removes as much of the tumor as possible. A thoracotomy is rarely able to completely remove all of the lung cancer and both mediastinoscopy and thoracotomy carry the risks of major surgical procedures (complications such as bleeding, infection, as well as risks of anesthesia and medications).
Blood tests: Blood tests alone cannot diagnose lung cancer. However, they may detect biochemical or metabolic abnormalities that are associated with cancer. For instance, elevated levels of calcium or the enzyme alkaline phosphatase have been associated with cancer that has metastasized to the bones. Also, elevated levels of certain enzymes normally present in liver cells, including aspartate aminotransferase and alanine aminotransferase, signal liver damage, possibly due to the presence of a metastatic tumor.