Everything about Lung Cancer totally explained
Lung cancer is a
disease of uncontrolled
cell growth in
tissues of the
lung. This growth may lead to
metastasis, invasion of adjacent tissue and infiltration beyond the lungs. The vast majority of primary lung cancers are
carcinomas of the lung, derived from
epithelial cells. Lung
cancer, the most common cause of cancer-related death in men and the second most common in women, is responsible for worldwide
annually. In the UK, it's the most common site of fatal cancer in both men and women. The most common
symptoms are shortness of breath, coughing (including
coughing up blood), and weight loss.
The main types of lung cancer are
small cell lung carcinoma and
non-small cell lung carcinoma. This distinction is important because the treatment varies; non-small cell lung carcinoma (NSCLC) is sometimes treated with
surgery, while small cell lung carcinoma (SCLC) usually responds better to
chemotherapy and radiation.
radon gas, including
second-hand smoke.
Lung cancer may be seen on
chest x-ray and
computed tomography (CT scan). The
diagnosis is confirmed with a
biopsy. This is usually performed via
bronchoscopy or CT-guided biopsy. Treatment and
prognosis depend upon the
histological type of cancer, the
stage (degree of spread), and the patient's
performance status. Possible treatments include surgery, chemotherapy, and
radiotherapy. With treatment, the five-year
survival rate is 14%.
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Sarcoma
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| Unspecified lung cancer
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The vast majority of lung cancers are
carcinomas—malignancies that arise from
epithelial cells. There are two main types of lung carcinoma, categorized by the size and appearance of the malignant cells seen by a
histopathologist under a
microscope:
non-small cell (80.4%) and
small-cell (16.8%) lung carcinoma. This classification, based on
histological criteria, has important implications for clinical management and prognosis of the disease.
Non-small cell lung carcinoma (NSCLC)
The non-small cell lung carcinomas are grouped together because their prognosis and management are similar. There are three main sub-types:
squamous cell lung carcinoma,
adenocarcinoma and large cell lung carcinoma.
Sub-types of non-small cell lung cancer>
| 0.1 |
| Adenoid cystic carcinoma |
0.04 |
| Other specified adenocarcinoma |
1.1 |
| Large cell carcinoma |
10.7 |
| Giant cell and spindle cell carcinoma |
0.4 |
| Other/unspecified non-small cell lung carcinoma |
8.9 |
Accounting for 31.1% of lung cancers,
Adenocarcinoma accounts for 29.4% of lung cancers. A subtype of adenocarcinoma, the
bronchioloalveolar carcinoma, is more common in female never-smokers, and may have different responses to treatment.
Accounting for 10.7% of lung cancers, It is often poorly
differentiated and tends to
metastasize early. While initially more sensitive to chemotherapy, it ultimately carries a worse prognosis and is often metastatic at presentation. Small cell lung cancers are divided into Limited stage and Extensive stage disease. This type of lung cancer is strongly associated with smoking.
Metastatic cancers
The lung is a common place for
metastasis from tumors in other parts of the body. These cancers are identified by the site of origin, thus a breast cancer metastasis to the lung is still known as breast cancer. They often have a characteristic round appearance on chest x-ray. Primary lung cancers themselves most commonly metastasize to the
adrenal glands, liver, brain, and bone. Small cell lung carcinoma is classified as
limited stage if it's confined to one half of the chest and within the scope of a single
radiotherapy field. Otherwise it's
extensive stage.
Signs and symptoms
Symptoms that suggest lung cancer include:
If the cancer grows in the
airway, it may obstruct airflow, causing
breathing difficulties. This can lead to accumulation of secretions behind the blockage, predisposing the patient to
pneumonia. Many lung cancers have a rich blood supply. The surface of the cancer may be fragile, leading to bleeding from the cancer into the airway. This blood may subsequently be coughed up.
Depending on the type of tumor, so-called
paraneoplastic phenomena may initially attract attention to the disease. In lung cancer, these phenomena may include
Lambert-Eaton myasthenic syndrome (muscle weakness due to
auto-antibodies),
hypercalcemia or
syndrome of inappropriate antidiuretic hormone (SIADH). Tumors in the top (apex) of the lung, known as
Pancoast tumors, may invade the local part of the
sympathetic nervous system, leading to changed sweating patterns and eye muscle problems (a combination known as
Horner's syndrome), as well as muscle weakness in the hands due to invasion of the
brachial plexus.
Many of the symptoms of lung cancer (
bone pain,
fever,
weight loss) are nonspecific; in the elderly, these may be attributed to
comorbid illness. Among male smokers, the lifetime risk of developing lung cancer is 17.2%. Among female smokers, the risk is 11.6%. This risk is significantly lower in non-smokers: 1.3% in men and 1.4% in women. Cigarette smoke contains over 60 known carcinogens including
radioisotopes from the
radon decay sequence,
nitrosamine, and
benzopyrene. Additionally, nicotine appears to depress the immune response to malignant growths in exposed tissue. The length of time a person smokes as well as the amount smoked increases the person's chance of developing lung cancer. If a person stops smoking, this chance steadily decreases as damage to the lungs is repaired and contaminant particles are gradually removed. Across the developed world, almost 90% of lung cancer deaths are caused by smoking. In addition, there's evidence that lung cancer in never-smokers has a better prognosis than in smokers, and that patients who smoke at the time of diagnosis have shorter survival than those who have quit.
Passive smoking—the inhalation of smoke from another's smoking—is a cause of lung cancer in non-smokers. Studies from the U.S., Europe, the UK, and Australia have consistently shown a significant increase in
relative risk among those exposed to passive smoke. Recent investigation of
sidestream smoke suggests it's more dangerous than direct smoke inhalation.
Radon gas
Radon is a colorless and odorless
gas generated by the breakdown of radioactive
radium, which in turn is the decay product of
uranium, found in the earth's
crust. The radiation decay products
ionize genetic material, causing mutations that sometimes turn cancerous. Radon exposure is the second major cause of lung cancer after smoking. Radon gas levels vary by locality and the composition of the underlying soil and rocks. For example, in areas such as
Cornwall in the UK (which has
granite as substrata), radon gas is a major problem, and buildings have to be force-ventilated with fans to lower radon gas concentrations. The
United States Environmental Protection Agency (EPA) estimates that one in 15 homes in the U.S. has radon levels above the recommended guideline of 4
picocuries per liter (pCi/L) (148
Bq/
m³).
Iowa has the highest average radon concentration in the United States; studies performed there have demonstrated a 50% increased lung cancer risk with prolonged radon exposure above the EPA's action level of 4 pCi/L.
Asbestos
Asbestos can cause a variety of lung diseases, including lung cancer. There is a
synergistic effect between tobacco smoking and asbestos in the formation of lung cancer. In the UK, asbestos accounts for 2–3% of male lung cancer deaths. Asbestos can also cause cancer of the
pleura, called
mesothelioma (which is different from lung cancer).
Viruses
Viruses are known to cause lung cancer in animals and recent evidence suggests similar potential in humans. Implicated viruses include
human papillomavirus,
JC virus,
simian virus 40 (SV40),
BK virus and
cytomegalovirus. These viruses may affect the
cell cycle and inhibit
apoptosis, allowing uncontrolled cell division.
Pathophysiology
oncogenes or inactivation of
tumor suppressor genes. Oncogenes are
genes that are believed to make people more susceptible to cancer.
Proto-oncogenes are believed to turn into oncogenes when exposed to particular carcinogens.
Mutations in the
K-ras proto-oncogene are responsible for 20–30% of non-small cell lung cancers.
Chromosomal damage can lead to
loss of heterozygosity. This can cause inactivation of tumor suppressor genes. Damage to chromosomes 3p, 5q, 13q and 17p are particularly common in small cell lung carcinoma. The
TP53 tumor suppressor gene, located on chromosome 17p, is often affected.
Several
genetic polymorphisms are associated with lung cancer. These include polymorphisms in
genes coding for
interleukin-1,
cytochrome P450,
apoptosis promoters such as
caspase-8, and DNA repair molecules such as
XRCC1. People with these polymorphisms are more likely to develop lung cancer after exposure to
carcinogens.
Diagnosis
Performing a
chest x-ray is the first step if a patient reports symptoms that may be suggestive of lung cancer. This may reveal an obvious mass, widening of the
mediastinum (suggestive of spread to
lymph nodes there),
atelectasis (collapse), consolidation (
pneumonia), or
pleural effusion. If there are no x-ray findings but the suspicion is high (such as a heavy smoker with blood-stained sputum),
bronchoscopy and/or a
CT scan may provide the necessary information. Bronchoscopy or CT-guided
biopsy is often used to identify the tumor type.
Policy interventions to decrease
passive smoking in public areas such as restaurants and workplaces have become more common in many Western countries, with California taking a lead in banning smoking in public establishments in 1998. Ireland played a similar role in Europe in 2004, followed by Italy and Norway in 2005, Scotland as well as several others in 2006, England in 2007, and France in 2008. New Zealand has banned smoking in public places as of 2004. The state of
Bhutan has had a complete smoking ban since 2005. In many countries, pressure groups are campaigning for similar bans. In 2007,
Chandigarh became the first city in
India to become 'smoke-free'.
Arguments cited against such bans are
criminalisation of smoking, increased risk of
smuggling and the risk that such a ban can't be enforced.
A 2008 study performed in over 75,000 middle-aged and elderly people demonstrated that the long-term use of supplemental multivitamins, such as vitamin C, vitamin E, and folate didn't reduce the risk of lung cancer. To the contrary, the study indicates that the long term intake of high doses of vitamin E supplements may even increase the risk of lung cancer.
Screening
Screening refers to the use of
medical tests to detect disease in asymptomatic people. Possible screening tests for lung cancer include
chest x-ray or
computed tomography (CT) of the chest. So far, screening programs for lung cancer have not demonstrated any clear benefit.
Randomized controlled trials are underway in this area to see if decreased long-term mortality can be directly observed from CT screening.
Treatment
Treatment for lung cancer depends on the cancer's specific cell type, how far it has
spread, and the patient's
performance status. Common treatments include
surgery,
chemotherapy, and
radiation therapy. Surgery is usually only an option in non-small cell lung carcinoma limited to one lung, up to stage IIIA. This is assessed with medical imaging (
computed tomography,
positron emission tomography). A sufficient pre-operative respiratory reserve must be present to allow adequate lung function after the tissue is removed.
Procedures include
wedge resection (removal of part of a lobe), segmentectomy (removal of an anatomic division of a particular lobe of the lung),
lobectomy (one lobe), bilobectomy (two lobes) or
pneumonectomy (whole lung). In patients with adequate respiratory reserve, lobectomy is the preferred option, as this minimizes the chance of local recurrence. If the patient doesn't have enough functional lung for this, wedge resection may be performed. Radioactive
iodine brachytherapy at the margins of wedge excision may reduce recurrence to that of lobectomy.
Chemotherapy
Small cell lung carcinoma is treated primarily with chemotherapy and radiation, as surgery has no demonstrable influence on survival. Primary chemotherapy is also given in metastatic non-small cell lung carcinoma.
The combination regimen depends on the tumor type. Non-small cell lung carcinoma is often treated with
cisplatin or
carboplatin, in combination with
gemcitabine,
paclitaxel,
docetaxel,
etoposide or
vinorelbine. In small cell lung carcinoma, cisplatin and etoposide are most commonly used. Combinations with carboplatin, gemcitabine, paclitaxel, vinorelbine,
topotecan and
irinotecan are also used.
Adjuvant chemotherapy for NSCLC
Adjuvant chemotherapy refers to the use of chemotherapy after surgery to improve the outcome. During surgery, samples are taken from the
lymph nodes. If these samples contain cancer, then the patient has stage II or III disease. In this situation, adjuvant chemotherapy may improve survival by up to 15%. Standard practice is to offer platinum-based chemotherapy (including either cisplatin or carboplatin).
Adjuvant chemotherapy for patients with stage IB cancer is controversial as clinical trials have not clearly demonstrated a survival benefit. Trials of preoperative chemotherapy (
neoadjuvant chemotherapy) in resectable non-small cell lung carcinoma have been inconclusive.
Radiotherapy
Radiotherapy is often given together with chemotherapy, and may be used with curative intent in patients with non-small cell lung carcinoma who are not eligible for surgery. This form of high intensity radiotherapy is called
radical radiotherapy. A refinement of this technique is continuous hyperfractionated accelerated radiotherapy (CHART), where a high dose of radiotherapy is given in a short time period. The use of adjuvant thoracic radiotherapy following curative intent surgery for non-small cell lung carcinoma isn't well established and controversial. Benefits, if any, may only be limited to those in whom the tumor has spread to the
mediastinal lymph nodes.
For both non-small cell lung carcinoma and small cell lung carcinoma patients, smaller doses of radiation to the chest may be used for symptom control (
palliative radiotherapy). Unlike other treatments, it's possible to deliver palliative radiotherapy without confirming the
histological diagnosis of lung cancer.
Patients with limited stage small cell lung carcinoma are usually given prophylactic cranial irradiation (PCI). This is a type of radiotherapy to the brain, used to reduce the risk of
metastasis. More recently, PCI has also been shown to be beneficial in those with extensive small cell lung cancer. In patients whose cancer has improved following a course of
chemotherapy, PCI has been shown to reduce the cumulative risk of brain
metastases within one year from 40.4% to 14.6%.
Recent improvements in targeting and imaging have led to the development of extracranial stereotactic radiation in the treatment of early-stage lung cancer. In this form of radiation therapy, very high doses are delivered in a small number of sessions using stereotactic targeting techniques. Its use is primarily in patients who are not surgical candidates due to medical
comorbidities.
Interventional radiology
Radiofrequency ablation should currently be considered an investigational technique in the treatment of bronchogenic carcinoma. It is done by inserting a small heat probe into the tumor to kill the tumor cells.
Targeted therapy
In recent years, various molecular targeted therapies have been developed for the treatment of advanced lung cancer.
Gefitinib (Iressa) is one such drug, which targets the
tyrosine kinase domain of the
epidermal growth factor receptor (EGF-R) which is expressed in many cases of non-small cell lung carcinoma. It wasn't shown to increase survival, although females, Asians, non-smokers and those with
bronchioloalveolar carcinoma appear to derive the most benefit from gefitinib. and has recently been approved by the FDA for second-line treatment of advanced non-small cell lung carcinoma. Similar to gefitinib, it appeared to work best in females, Asians, non-smokers and those with bronchioloalveolar carcinoma.
The
angiogenesis inhibitor bevacizumab (in combination with
paclitaxel and
carboplatin) improves the survival of patients with advanced non-small cell lung carcinoma. However this increases the risk of lung bleeding, particularly in patients with
squamous cell carcinoma.
Advances in cytotoxic drugs,
pharmacogenetics and targeted drug design show promise. A number of targeted agents are at the early stages of clinical research, such as
cyclo-oxygenase-2 inhibitors, the
apoptosis promoter
exisulind,
proteasome inhibitors,
bexarotene and vaccines. Future areas of research include
ras proto-oncogene inhibition,
phosphoinositide 3-kinase inhibition,
histone deacetylase inhibition, and
tumor suppressor gene replacement.
Prognosis
tumor size, cell type (
histology), degree of spread
(stage) and
metastases to multiple
lymph nodes, and vascular invasion. For patients with inoperable disease, prognosis is adversely affected by poor
performance status and weight loss of more than 10%. Prognostic factors in small-cell lung cancer include
performance status,
gender, stage of disease, and involvement of the
central nervous system or
liver at the time of
diagnosis.
For non-small cell lung carcinoma, prognosis is generally poor. Following complete surgical resection of stage IA disease, five-year survival is 67%. With stage IB disease, five-year survival is 57%. The 5-year survival rate of patients with stage IV NSCLC is about 1%.
For small cell lung carcinoma, prognosis is also generally poor. The overall five-year survival for patients with SCLC is about 5%.
Epidemiology
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, with the highest rates in Europe and North America. The population segment most likely to develop lung cancer is over-fifties who have a history of smoking. Lung cancer is the second most commonly occurring form of cancer in most western countries, and it's the leading cancer-related cause of death. Although the rate of men dying from lung cancer is declining in western countries, it's actually increasing for women due to the increased takeup of smoking by this group. Among lifetime non-smokers, men have higher age-standardized lung cancer death rates than women.
Not all cases of lung cancer are due to smoking, but the role of
passive smoking is increasingly being recognized as a risk factor for lung cancer, leading to policy interventions to decrease undesired exposure of non-smokers to others' tobacco smoke. Emissions from automobiles, factories and power plants also pose potential risks.
Eastern Europe has the highest lung cancer mortality among men, while northern Europe and the U.S. have the highest mortality among women.Lung cancer incidence is currently less common in developing countries. With increased smoking in developing countries, the incidence is expected to increase in the next few years, notably in China and India.
Lung cancer incidence (by country) has an inverse correlation with
sunlight and
UVB exposure. One possible explanation is a preventative effect of
vitamin D (which is produced in the skin on exposure to sunlight).
History
Lung cancer was extremely rare before the advent of cigarette smoking; it wasn't even recognized as a distinct disease until 1761. Different aspects of lung cancer were described further in 1810. Malignant lung tumors made up only 1% of all cancers seen at autopsy in 1878, but had risen to 10–15% by the early 1900s. Case reports in the medical literature numbered only 374 worldwide in 1912, but a review of autopsies showed that the incidence of lung cancer had increased from 0.3% in 1852 to 5.66% in 1952. In
Germany, in 1929 physician Fritz Lickint recognized the link between smoking and lung cancer, The
British Doctors Study, published in the 1950s, was the first solid
epidemiological evidence of the link between lung cancer and smoking. As a result, in 1964 the
Surgeon General of the United States recommended that smokers should stop smoking.
The connection with
radon gas was first recognized among miners in the
Ore Mountains near
Schneeberg, Saxony.
Silver has been mined there since 1470, and these mines are rich in
uranium, with accompanying
radium and radon gas. Miners developed a disproportionate amount of lung disease, eventually recognized as lung cancer in the 1870s and an estimated 75% of former miners died from lung cancer. Despite this discovery, mining continued into the 1950s due to the
USSR's demand for uranium.
Treatment
The first successful
pneumonectomy for lung cancer was carried out in 1933 and initially, pneumonectomy was the surgical treatment of choice. However, with improvements in
cancer staging and surgical techniques,
lobectomy with
lymph node dissection has now become the treatment of choice.
Palliative
radiotherapy has been used since the 1940s. In 1997, continuous hyperfractionated accelerated radiotherapy (CHART) was seen as an improvement over conventional radical radiotherapy.
With small cell lung carcinoma, initial attempts in the 1960s at surgical resection and radical radiotherapy were unsuccessful. In the 1970s, successful chemotherapy regimens were developed.
Further Information
Get more info on 'Lung Cancer'.
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