by: Peter Crosta
Cancer is a class of diseases characterized by out-of-control cell growth, and lung cancer occurs when this uncontrolled cell growth begins in one or both lungs. Rather than developing into healthy, normal lung tissue, these abnormal cells continue dividing and form lumps or masses of tissue called tumors. Tumors interfere with the main function of the lung, which is to provide the bloodstream with oxygen to be carried to the entire body. If a tumor stays in one spot and demonstrates limited growth, it is generally considered to be benign.
More dangerous, or malignant, tumors form when the cancer cells migrate to other parts of the body through the blood or lymph system. When a tumor successfully spreads to other parts of the body and grows, invading and destroying other healthy tissues, it is said to have metastasized. This process itself is called metastasis, and the result is a more serious condition that is very difficult to treat.
Lung cancer is called “primary” if the cancer originates in the lungs and “secondary” if it originates elsewhere in the body but has metastasized to the lungs. These two types are considered different cancers from diagnostic and treatment perspectives.
In 2007, about 15% of all cancer diagnoses and 29% of all cancer deaths were due to lung cancer. It is the number one cause of death from cancer every year and the second most diagnosed after breast and prostate cancers (for women and men, respectively). Lung cancer is usually found in older persons because it develops over a long period of time.
How is lung cancer classified?
Lung cancer can be broadly classified into two main types based on the cancer’s appearance under a microscope: non-small cell lung cancer and small cell lung cancer. Non-small cell lung cancer (NSCLC) accounts for 80% of lung cancers, while small cell lung cancer accounts for the remaining 20%.
NSCLC can be further divided into four different types, each with different treatment options:
• Squamous cell carcinoma or epidermoid carcinoma. As the most common type of NSCLC and the most common type of lung cancer in men, squamous cell carcinoma forms in the lining of the bronchial tubes.
• Adenocarcinoma. As the most common type of lung cancer in women and in nonsmokers, adenocarcinoma forms in the mucus-producing glands of the lungs.
• Bronchioalveolar carcinoma. This type of lung cancer is a rare type of adenocarcinoma that forms near the lungs’ air sacs.
• Large-cell undifferentiated carcinoma. A rapidly growing cancer, large-cell undifferentiated carcinomas form near the outer edges or surface of the lungs.
Small cell lung cancer (SCLC) is characterized by small cells that multiply quickly and form large tumors that travel throughout the body. Almost all cases of SCLC are due to smoking.
What causes cancer?
Cancer is ultimately the result of cells that uncontrollably grow and do not die. Normal cells in the body follow an orderly path of growth, division, and death. Programmed cell death is called apoptosis, and when this process breaks down, cancer begins to form. Unlike regular cells, cancer cells do not experience programmatic death and instead continue to grow and divide. This leads to a mass of abnormal cells that grows out of control.
Lung cancer occurs when a lung cell’s gene mutation makes the cell unable to correct DNA damage and unable to commit suicide. Mutations can occur for a variety of reasons. Most lung cancers are the result of inhaling carcinogenic substances.
Carcinogens are a class of substances that are directly responsible for damaging DNA, promoting or aiding cancer. Tobacco, asbestos, arsenic, radiation such as gamma and x-rays, the sun, and compounds in car exhaust fumes are all examples of carcinogens. When our bodies are exposed to carcinogens, free radicals are formed that try to steal electrons from other molecules in the body. These free radicals damage cells and affect their ability to function and divide normally.
About 87% of lung cancers are related to smoking and inhaling the carcinogens in tobacco smoke. Even exposure to second-hand smoke can damage cells so that cancer forms.
Cancer can be the result of a genetic predisposition that is inherited from family members. It is possible to be born with certain genetic mutations or a fault in a gene that makes one statistically more likely to develop cancer later in life. Genetic predispositions are thought to either directly cause lung cancer or greatly increase one’s chances of developing lung cancer from exposure to certain environmental factors.
What are the symptoms of lung cancer?
Cancer symptoms are quite varied and depend on where the cancer is located, where it has spread, and how big the tumor is. Lung cancer symptoms may take years before appearing, usually after the disease is in an advanced stage.
Many symptoms of lung cancer affect the chest and air passages. These include:
• Persistent or intense coughing
• Pain in the chest shoulder, or back from coughing
• Changes in color of the mucus that is coughed up from the lower airways (sputum)
• Difficulty breathing and swallowing
• Hoarseness of the voice
• Harsh sounds while breathing (stridor)
• Chronic bronchitis or pneumonia
• Coughing up blood, or blood in the sputum
If the lung cancer spreads, or metastasizes, additional symptoms can present themselves in the newly affected area. Swollen or enlarged lymph nodes are common and likely to be present early. If cancer spreads to the brain, patients may experience vertigo, headaches, or seizures. In addition, the liver may become enlarged and cause jaundice and bones can become painful, brittle, and broken. It is also possible for the cancer to infect the adrenal glands resulting in hormone level changes.
As lung cancer cells spread and use more of the body’s energy, it is possible to present symptoms that may also be associated with many other ailments. These include:
• Unexplained weight loss
• Pain in joints or bones
• Problems with brain function and memory
• Swelling in the neck or face
• General weakness
• Bleeding and blood clots
How is lung cancer diagnosed and staged?
Physicians use information revealed by symptoms as well as several other procedures in order to diagnose lung cancer. Common imaging techniques include chest X-rays, bronchoscopy (a thin tube with a camera on one end), CT scans, MRI scans, and PET scans. Physicians will also conduct a physical examination, a chest examination, and an analysis of blood in the sputum. All of these procedures are designed to detect where the tumor is located and what additional organs may be affected by it.
Although the above diagnostic techniques provided important information, extracting cancer cells and looking at them under a microscope is the only absolute way to diagnose lung cancer. This procedure is called a biopsy. If the biopsy confirms lung cancer, a pathologist will determine whether it is non-small cell lung cancer or small cell lung cancer.
After a diagnosis is made, an oncologist will determine the stage of the cancer by finding out how far the cancer has spread. The stage determines which choices will be available for treatment and informs prognosis. The most common cancer staging method is called the TNM system. T (1-4) indicates the size and direct extent of the primary tumor, N (0-3) indicates the degree to which the cancer has spread to nearby lymph nodes, and M (0-1) indicates whether the cancer has metastasized to other organs in the body. A small tumor that has not spread to lymph nodes or distant organs may be staged as (T1, N0, M0), for example.
For non-small cell lung cancer, TNM descriptions lead to a simpler categorization of stages. These stages are labeled from I to IV, where lower numbers indicate earlier stages where the cancer has spread less. More specifically:
• Stage I is when the tumor is found only in one lung and in no lymph nodes.
• Stage II is when the cancer has spread to the lymph nodes surrounding the infected lung.
• Stage IIIa is when the cancer has spread to lymph nodes around the trachea, chest wall, and diaphragm, on the same side as the infected lung.
• Stage IIIb is when the cancer has spread to lymph nodes on the other lung or in the neck.
• Stage IV is when the cancer has spread throughout the rest of the body and other parts of the lungs.
Small cell lung cancer has two stages: limited or extensive. In the limited stage, the tumor exists in one lung and in nearby lymph nodes. In the extensive stage, the tumor has infected the other lung as well as other organs in the body.
How is lung cancer treated?
Lung cancer treatments depend on the type of cancer, the stage of the cancer (how much it has spread), age, health status, and additional personal characteristics. As there is usually no single treatment for cancer, patients often receive a combination of therapies and palliative care. The main lung cancer treatments are surgery, chemotherapy, and/or radiation. However, there also have been recent developments in the fields of immunotherapy, hormone therapy, and gene therapy.
Surgery is the oldest known treatment for cancer. If a cancer is in stage I or II and has not metastasized, it is possible to completely cure a patient by surgically removing the tumor and the nearby lymph nodes. After the disease has spread, however, it is nearly impossible to remove all of the cancer cells.
Lung cancer surgery is performed by a specially trained thoracic surgeon. After removing the tumor and the surrounding margin of tissue, the margin is further studied to see if cancer cells are present. If no cancer is found in the tissue surrounding the tumor, it is considered a “negative margin.” A “positive margin” may require the surgeon to remove more of the lung tissue.
Lung cancer surgery can be curative or palliative. Curative surgery aims to cure a patient with early stage lung cancer by removing all of the cancerous tissue. Palliative surgery aims to remove an obstruction or open an airway, making the patient more comfortable but not necessarily removing the cancer.
Surgery carries side effects – most notably pain and infection. Lung cancer surgery is an invasive procedure that can cause harm to the surrounding body parts. Doctors will usually provide several options for alleviating any pain from surgery. Antibiotics are commonly used to prevent infections that may occur at the site of the wound or elsewhere inside the body.
Radiation treatment, also known as radiotherapy, destroys or shrinks lung cancer tumors by focusing high-energy rays on the cancer cells. This causes damage to the molecules that make up the cancer cells and leads them to commit suicide. Radiotherapy utilizes high-energy gamma-rays that are emitted from metals such as radium or high-energy x-rays that are created in a special machine. Radiation can be used as the main treatment for lung cancer, to kill remaining cells after surgery, or to kill cancer cells that have metastasized.
Early radiation treatments caused severe side-effects because the energy beams would damage normal, healthy tissue, but technologies have improved so that beams can be more accurately targeted. Radiation oncologists can focus the radiation in precise locations in the body for certain lengths of time, reducing the risk of damage to surrounding healthy tissue. Treatments occur intermittently over weeks or months depending on the size and extent of the tumor, the dosage of radiation, and how much damage is being done to noncancerous tissue.
Common side effects of radiation therapy include fatigue, nausea, loss of appetite, hair loss, and skin affectations that cause skin to become dry, irritated, and sensitive.
Chemotherapy utilizes strong chemicals that interfere with the cell division process – damaging proteins or DNA – so that cancer cells will commit suicide. These treatments target any rapidly dividing cells (not just cancer cells), but normal cells usually can recover from any chemical-induced damage while cancer cells cannot. Chemotherapy is considered systemic because its medicines travel throughout the entire body, killing the original tumor cells as well as cancer cells that have spread throughout the body.
A medical oncologist will usually prescribe chemotherapy drugs for lung cancer to be taken intravenously, but there are also drugs available in tablet, capsule, and liquid form. Chemotherapy treatment occurs in cycles so the body has time to heal between doses, and dosages are determined by the type of lung cancer, the type of drug, and how the person responds to treatment. Medicines may be administered daily, weekly, or monthly, and can continue for months or even years.
Combination therapies often include multiple types of chemotherapy, and chemotherapy is also given as adjuvant therapy as a complement to surgery and radiation. Adjuvant therapy is designed to reduce the risk of cancer recurrence after surgery and killing any cancer cells that exist after surgery. Chemotherapy can be given before surgery, called neo-adjuvant therapy, to shrink tumors and to make surgery more successful.
Chemotherapy carries several common side effects, but they depend on the type of chemotherapy and the health of the patient. These include nausea and vomiting, appetite loss, diarrhea, hair loss, fatigue from anemia, infections, bleeding, and mouth sores. Many of these side effects are only temporarily felt during treatment, and several drugs exist to help patients cope with the symptoms.
Researchers continue to search for ways to improve lung cancer treatments and find new methods of treating the disease. Targeted therapies are designed to only treat cancer cells while leaving alone normal and healthy lung cells. These include monoclonal antibodies that travel directly to the cancer cells and release drugs or radiation, anti-angiogenesis agents that interfere with the blood supply creation mechanism of cancer cells, and growth factor inhibitors that block the effects of growth factors and disallow the cancerous cells to grow. There is also some research in the area of lung cancer vaccines that first transform cancer cells so they are no longer cancerous. However, the cells will exist such that the body’s immune system can recognize the cancerous cells as foreign and attack them. These targeted therapies are also called immunotherapies because the treatment tweaks the body’s natural immune responses.
How can lung cancer be prevented?
Cancers that are closely linked to certain behaviors are the easiest to prevent. For example, choosing not to smoke tobacco or drink alcohol significantly lowers the risk of several types of cancer – most notably lung, throat, mouth, and liver cancer. Even if you are a current tobacco user, quitting can still greatly reduce your chances of getting cancer. The most important preventive measure you can take to avoid lung cancer is to quit smoking.
Quitting smoking will also reduce your risk of several other types of cancer including esophagus, pancreas, larynx, and bladder cancer. If you quit smoking, you will usually reap additional benefits such as lower blood pressure, enhanced blood circulation, and increased lung capacity.
Exposure to tobacco smoke is not the only risk factor for lung cancer though. Those who have come into contact with asbestos, radon, and secondhand smoke also have an increased risk of developing lung cancer. In addition, having a family member who developed lung cancer without being exposed to carcinogens could mean that you have a genetic predisposition for developing the disease, increasing your overall risk.
Screening techniques are designed to find cancer at the earliest stage so that the most treatment options are available, increasing survival rates and avoiding highly invasive procedures. Most lung cancers are detected in the late stages of the disease after they have spread and are harder to treat. Although there currently do not exist approved screening tests for lung cancer that improve survival or detect localized disease, there is promising research underway. Advocates of screening recommend that certain high risk groups be screened. This includes persons age 60 or older with a history of smoking, previous lung tumors, or chronic obstructive pulmonary disease (COPD). Possible lung cancer screening tests include analysis of sputum cells, fiberoptic examination of bronchial passages (bronchoscopy), and low-dose spiral CT scans.