Lung cancer overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Kim-Son H. Nguyen, M.D., M.P.A., Beth Israel Deaconess Medical Center, Harvard Medical School, Boston MA, Cafer Zorkun, M.D., Ph.D. [2]
Overview
The pathogenesis of colorectal carcinoma (CRC) involves the molecular pathways for both sporadic and colitis-associated CRC. There are both genetic and environmental causes of colorectal carcinoma (CRC). Colorectal cancer may be differentiated from other diseases that cause unexplained weight loss, unexplained loss of appetite, nausea, vomiting, diarrhea, anemia, jaundice, and fatigue, such as irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), hemorrhoids, anal fissures, and diverticular disease. Colorectal cancer is the third most commonly diagnosed cancer in the world, and accounts for 8% of all cancer-related deaths annually. There are both genetic and environmental factors that can increase the risk of colorectal carcinoma (CRC). Current guidelines recommend that colonoscopy is the optimal screening tool for colon cancer since it detects 98-99% of the cases. The progression from an edematous polyp to colorectal cancer may take 10-15 years. Colorectal cancer staging is an estimate of the amount of penetration of the cancer. Staging is based on the TNM classification system which depends on the extent of local invasion, the degree of lymph node involvement, and whether there is distant metastasis. The history of a patient with colorectal cancer may include a family history of polyps/colorectal cancer or a history of inflammatory bowel disease. Some symptoms that are associated with colorectal cancer are change in bowel habits, hematochezia, and rectal pain. Metastatic symptoms include dyspnea, abdominal pain, fractures, and confusion. Generally, the most common signs of colorectal cancer are emaciation, lethargy, and pallor Other signs include low-grade fever, discomfort on palpation, ascitesrectal bleeding, rectal mass, and jaundice. The laboratory findings associated with colorectal carcinoma are the following: CBC, FOBT, serum CEA and CA 19-9 concentration, serum iron concentrations, serum vitamin B12 and folate concentrations, liver function tests, and pulmonary function tests. Chest radiography (CXR) is the initial imaging modality used in the detection of suspected pulmonary metastasis. CT scan is used to determine the extent of involvement on colon cancer, most commonly in the abdomen and lungs. Other imaging tests that can be used for colorectal cancer are MRI, ultrasound, endoscopy, PET scan, barium study, and angiography. A biopsy and genetic testing can be performed when a suspected lesion is found on colonoscopy. Chemotherapy is used to reduce the likelihood of metastasis developing, shrink tumor size, and slow tumor growth. Surgery remains the primary treatment while chemotherapy and/or radiotherapy may be recommended depending on the individual patient's staging and other medical factors. When colorectal cancer metastasizes, there will be a different approach than with a localized tumor. The most common site of metastasis is the liver, and the second most common is the lung.
Historical Perspective
Today, lung cancer is one of the leading causes of death worldwide, killing over 1 million people per year but it was not always that way. Approximately 150 years ago, lung cancer was actually a very rare disease. At the Institute of Pathology of the University of Dresden in Germany, lung cancer represented only 1% of all cancers seen at autopsy. Lung cancer steadily rose from this point on and in 1918 the percentage had risen to nearly 10% and by 1927, it represented more than 14% of all cancers. Around this time period, the disease had a life expectancy from about 6 months to 2 years and in most cases, the afflicted individual had had long term chronic bronchitis.
Classification
Primary lung cancer can be classified into two main categories: small cell lung cancer (~15%) and non small cell lung cancer (~85%). Non small cell lung cancer includes several subtypes grouped together because their prognosis and management are similar. The 2004 WHO histological classification of tumors of the lung categorized lung tumors into malignant epithelial tumors, benign epithelial tumors, lymphoproliferative tumors, miscellaneous tumors, and metastatic tumors.
Pathophysiology
The pathophysiology consists of genetics, smoking, radon gas, asbestos, viruses, infection, and inflammation.
Causes
The main causes of any cancer include carcinogens (such as those in tobacco smoke), ionizing radiation, and viral infection. This exposure causes cumulative changes to the DNA in the tissue lining the bronchi of the lungs (the bronchial epithelium). As more tissue becomes damaged, eventually a cancer develops.Lung cancer is the deadliest type of cancer for both men and women. Each year, more people die of lung cancer than breast, colon, and prostate cancers combined.
Differential Diagnosis
Lung cancer may be differentiated from other diseases that cause hemoptysis, cough, dyspnea, wheeze, chest pain, dysphonia, dysphagia, unexplained weight loss, unexplained loss of appetite, and fatigue such as pneumonia, bronchitis, metastatic cancer from a non-thoracic primary site, infectious granuloma, pulmonary tuberculosis, tracheal tumors, and a thyroid mass.
Epidemiology and Demographics
Worldwide, lung cancer is the most common cancer in terms of both incidence and mortality with 1.35 million new cases per year and 1.18 million deaths. The highest rates are observed in Europe and North America. The population segment most likely to develop lung cancer is those individuals over-fifty years of age who have a history of smoking. Although the rate of men dying from lung cancer is declining in western countries, it is actually increasing for women due to their increased rate of smoking. Among lifetime non-smokers, men have higher age-standardized lung cancer death rates than women. The expected number for new cases of lung cancerin the United States for 2014 is 224,210.
Risk Factors
Lung cancer is the deadliest type of cancer for both men and women. Each year, more people die of lung cancer than breast, colon, and prostate cancers combined.
Screening
Lung cancer screening is a strategy used to identify early lung cancer in people, before they develop symptoms. Screening refers to the use of medical tests to detect disease in asymptomatic people. Screening studies for lung cancer have only been done in high risk populations, such as smokers and workers with occupational exposure to certain substances. This is because radiation exposure from screening could actually induce carcinogenesis|cancer formation in a small percentage of screened subjects, so this risk should be mitigated by a (relatively) high prevalence of lung cancer in the population being screened. A pulmonary nodule larger than 5 to 6 mm is considered a positive result for screening with x-ray or computed tomography.
Natural History, Complications, and Prognosis
The majority of lung cancers present with advanced disease because the symptoms tend to occur later in the course of the disease. The patient experiences non-specific symptoms such as cough, hemoptysis, dyspnea, chest pain, dysphonia, dysphagia, fatigue, lack of appetite, weight loss, and fatigue from 3 weeks to 3 months before seeking medical attention. There are a variety of complications associated with lung cancer such as pleural effusion, leg weakness paresthesias, bladder/bladder dysfunction, seizures, hemiplegia, cranial nerve palsies, confusion, personality changes, skeletal pain, and/or pleuritic pain, atelectasis, and/or bronchopleural fistula. The prognosis of lung cancer is poor if diagnosed during the advanced stages.
Staging
Lung cancer staging is an assessment of the degree of spread of the cancer from its original source. It is an important factor affecting the prognosis and potential treatment of lung cancer. Non-small cell lung carcinoma is staged from IA ("one A", best prognosis) to IV ("four", worst prognosis).[1] Small cell lung carcinoma is classified as limited stage and extensive stage.
History and Symptoms
Many of the symptoms of lung cancer (bone pain, fever, weight loss) are nonspecific; in the elderly, these may be attributed to comorbid illness. In many patients, the cancer has already spread beyond the original site by the time they have symptoms and seek medical attention. Common sites of metastasis include the bone, such as the spine (causing back pain and occasionally spinal cord compression), the liver and the brain. About 10% of people with lung cancer do not have symptoms at diagnosis; these cancers are incidentally found on routine chest x-rays.
Physical Examination
Generally, the most common signs of lung cancer are decreased/absent breath sounds, wheeze, chest pain, emaciation, lethargy, and pallor. Other signs include metastases to the liver, brain, and adrenal glands (Cushing's syndrome).
Diagnostic Studies
Laboratory Findings
The laboratory findings associated with lung cancer are the following: neutropenia, hyponatremia, hypokalemia, hypercalcemia, respiratory acidosis, hypercarbia, hypoxia, and tumor cells in sputum and pleural effusion cytology.
X-Ray
Performing a chest x-ray is the first step if a patient reports symptoms that may be suggestive of lung cancer. Often lung cancers are picked up on a routine chest X-ray in a person experiencing no symptoms.
CT
CT scans help stage the lung cancer. A CT scan of the abdomen and brain can help visualize the common sights of metastases: adrenal glands, liver, and brain. CT scans diagnose lung cancer by providing anatomical detail to locate the tumor, demonstrating proximity to nearby structures, and deciphering whether lymph nodesare enlarged in the mediastinum.
MRI
MRI is useful for the evaluation of a patient with spinal cord compression, superior sulcus tumors, and brachial plexus tumors.
Biopsy
A transthoracic needle biopsy and a bronchoscopy are conducted to diagnose lung cancer.
Other Diagnostic Studies
Other diagnostic tests include bone scintigraphy, PET scan, and molecular tests.
Medical Therapy
The medical therapy for lung cancer consists of surgery, radiation therapy, chemotherapy, and targeted therapy.
Surgery
Lung cancer surgery describes the use of surgical operations in the treatment of lung cancer. It involves the surgical excision of cancer tissue from the lung. It is used mainly in non-small cell lung cancer with the intention of curing the patient.
Primary Prevention
Smoking cessation and avoidance of second hand smoking are the most important measures for the prevention of lung cancer. Lifestyle changes, such as healthy diet rich with fruits and vegetables and regular exercise, might decrease the risk of developing cancer in general.
Secondary Prevention
Secondary prevention for lung cancer consists of smoking cessation and screening. Secondary chemoprevention focuses on blocking the development of lung cancer in individuals in whom a precancerous lesion has been detected.
References