OVERVIEW

Seated in the chest cavity around each side of the heart is an organ called the Lung.

This organ is responsible for the delivering of oxygen to the blood by capturing it from the atmosphere. It also in return pull out of carbon dioxide from the blood and send it out of the body. Cancer of the lung is one of the most common cancers in the world. Though other factors like; air pollutants and radiations can increase the possibility of having lung cancer, Smoking of tobacco is the most common factor known to cause lung cancer. Smoking for a very long time, smoking a lot of cigarettes in a person’s lifetime increases the risk of developing lung cancer.

DEFINITION

Abnormal growth of cells and the ability of the abnormal cells in the lung to spread or invade other tissues is called lung cancer. Simply, lung cancer is cancer that begins in the cells of the lungs. This abnormal growth in the lungs is most commonly from the cells that cover the glandular tissues of the lung. This cancer type is called Adenocarcinoma.

TYPES OF LUNG CANCER 

Lung cancer is classified into different types. These classifications are explained below;

1. CLASSIFICATION BASED ON APPEARANCE OF CANCER CELLS UNDER MICROSCOPE.

When cancer cells are observed under microscope histological differences are made. Due to this lung cancers are mainly grouped into ;

A.NON SMALL CELL CARCINOMA (NSCC)

This type of lung cancer is the most common of all lung cancers diagnosed. They are normally of epithelial cells origin. About  80% of lung cancer cases diagnosed in the USA  are this type of cancers. Based on the specific Kind of cells found under the microscope NSCC  is grouped into three main forms.

1.ADENOCARCINOMA; This kind of cancer occurs in both smokers and non-smokers. In the case of non-smokers, women are the most affected. Adenocarcinoma is the most common type of non-small cell carcinomas. In the USA it ranks about 40% of lung cancer cases. It normally develops in the respiratory bronchioles (smaller airways ) and the outer borders of the lung. It mostly originates from the epithelial cells of mucus secretory (glandular-like) tissues of the lung. This type of cancer can spread to nearby tissues or even distant organs. Examples are; Adenocarcinoma in situ(Bronchioloalveolar carcinoma); which does not invade nor spread.

.Minimally Invasive Adenocarcinoma; which can invade to a very lesser extent.

.Invasive Adenocarcinoma; which invades and spread to other tissues.

2.SQUAMOUS CELL CARCINOMA; This is the second most common type of NSCC.It makes up about 25% of lung cancer cases. It is mostly caused by cigarette smoking and affects men mostly than women. It normally originates from the lower part of the conducting system of the respiratory tract bronchi. It becomes large and forms cavities in the lungs. The cancerous cells can grow bigger and invade neighbouring tissues and may even spread to other distant organs.

3.LARGE CELL CARCINOMAS; As the name depicts, these cancer is known by very large cell size. The cells have broad cytoplasmic size relative to their nucleus size. It forms about 5 % to 10% of all NSCC. The cells can grow faster and can invade nearby structures or spread to distant body parts. They are mostly undifferentiated cells.

B.SMALL CELL CARCINOMA (SCC)

This type of cancer is characterized by small cells under a microscope . It makes about 15% of lung cancer cases and it’s mostly related to tobacco smoking. It is very aggressive and it easily invades nearby tissues and spreads to distant organs. Due to the flat nature of these cells with their small cytoplasmic demarcations, they are called Oat cell carcinoma. This kind of cancer has a very poor prognosis due to its early malignancy. Small cell carcinomas can be in two stages based on the extent of invasion or spread.

1. Limited Stage; Cancer Cells remain at one side of the chest in one lung and surrounding lymph nodes.

2.Extensive Stage; Cancer Cells affect both sides of the chest with both lungs and spread to distant organs.

 Furthermore, small cell carcinoma is also called neuroendocrine cancer. This is because these small cancerous cells contain secretory granules which respond to neuronal stimulation and produce hormones ectopic hormones. When these hormones affect human metabolism negatively it is known as a paraneoplastic   syndrome.

 

C.COMBINED OR MIXED SMALL CELL CARCINOMA

This type is a rare type of lung cancer in which cells observed have both non-small cells and small cells mixed together. A histological finding of any of the types of non-small cell carcinoma mixed up with small cell carcinoma after a sample observation is known as combined small cell carcinoma.

 D.OTHERS

1.CARCINOID TUMORS; These are non-aggressive neoplastic growths normally of bronchial origin. They can produce hormones which can affect body metabolism. These tumours are very rare and are not caused by the smoking of cigarettes or other tobacco products.

2.MESOTHELIOMA; These Cancers occur in the cells that line the pleural cavity. It sometimes affects the visceral cover of the lung. These tumours are rare and non-aggressive.

3.SARCOMA; These abnormal cells originate from connective tissues of the lungs. These tissues are; blood vessels, muscles and others. This is also a very rare form of lung cancer.

 

2. CLASSIFICATION BASED ON THE SOURCE OF CANCER CELLS.

This is based on the fact that the cancer cells are of the lung origin or from other distant organs due to metastasis.

A.PRIMARY LUNG CANCER; The cancer cells found in the lung originated from the cells of the lung. The cells can be from the conducting airway, respiratory airway, alveolar and even blood vessels of the lungs.

B.SECONDARY LUNG CANCER; The cancerous cells originate from distant organs like bones, breast, thyroid.The cancerous cells spread to the lung from the organs mentioned above and cause respiratory symptoms like; dyspnea and Chest pain. These cells normally look like round balls (Cannonballs)  on radiological images like; Computed Tomography(CT)  scan.

EPIDEMIOLOGY

In the United States of America, about 162,000 people died out of the lung cancer diagnosed cases of 240,000 in the year 2010. This makes lung cancer the most common cause of cancer death in the USA. Lung cancer is leading cancer in the world based on the frequency of occurrence and death rate

A new lung cancer diagnosis makes up about 12 % of all cancer diagnosis in the world with a mortality rate of about 18%  of all cancer deaths. Lung cancer follows breast cancer as the leading cause of all cancer deaths in women.

High incidences of lung cancer are recorded in Europe, North America, Eastern part of Asia and most of these cases are related to smoking of tobacco.

Men above age 50 with past smoking history or who are still active smokers are likely to develop lung cancer. The incidence and mortality rate of lung cancer is of lesser values in Africa and the southern parts of Asia.

CANCER RESEARCH BUDGET PER YEAR

Lung cancer is an issue of global concern due to its high incidence and mortality rates.Constant research programs are always made in order to reduce the frequency of occurrence and the number of lives claimed by lung cancer through out the world .In the light of this ,the American government allocates funds for cancer research.The estimated amount given to the National Cancer institute  dating from the year 2012 to 2017  for lung cancer is about 1,717.0 billion dollars .The estimated amount for lung cancer research per year is about 280.0 million dollars.

Aside the government support for cancer research programs ,other non governmental organizations help in funding cancer research programs .

CAUSES OF LUNG CANCER

1.Smoking; Longtime tobacco smoking is the most common cause of lung cancer. The ability of tobacco products people smoke to release carcinogens is high that even people who inhale the smoke constantly Secondhand smokers can also get lung cancer. Aside from this, lung cancer cases can occur in people who don’t smoke and are also not second-hand smokers.

 2. Randon gas; It’s a radioactive gas which can cause lung cancer when inspired constantly. Randon gas converts genetic materials into ions and cause mutations.

 3.Other substances; Asbestos, arsenic, chromium which are inhaled constantly in an air polluted environment.

4. Inherited Genetic mutations; Alterations in the genetic makeup of an individual is an underlying risk for developing lung cancer especially when environmental factors are added.

RISK FACTORS OF LUNG CANCER

1.Being a smoker of tobacco products.

2.Constantly inhaling smoke from tobacco products (Second-hand smoking)

3.Exposure and inhalation of randon gas, and other carcinogens.

4.Old age mostly with smokers.

5.Family history of lung cancer.

PATHOPHYSIOLOGY

The mechanism of lung cancer just like most  other cancers are due to alterations in the genes that regulate the cell proliferation and cell death in the human body.This gene alterations result in the deficiency of cell proliferation check points which check for abnormalities of dividing cells and regulate the speed and extent of proliferation.

Smoking causes mutations which is not inherited from parents of an individual.Tobacco smoking introduces carcinogens ,example benzopyrene into the cell wall which bind to genetic materials and cause mutations and cell damage.This kind of mutation is called Induced mutation.This mutation is different for the inherited mutations called Spontaneous mutations.

The result of this is the abnormal growth of cells in the lungs .

CLINICAL MANIFESTATIONS OF LUNG CANCER

A.Early manifestations of cancer

1.A persistent cough that worsens with time.

2. Coughing up of blood.

3.Wheezing

4.Shortness of breath.

5.Hoarseness(dysphonia)

6.Fatigue

7.Unexplained weight loss

8.Loss of appetite.

B.Complications resulting from invasion and spread of cancer to distant organs; bones, brain, liver

1.Excessive Pain In bones.

2.Jaundice if Cancer spreads to the liver

3.Headache

4.Dizziness

5.Loss of balance.

6.Loss of sensation in the arms and legs.

7.Clubbing of fingers

C.PARANEOPLASTIC. SYNDROME

These manifestations are only caused mostly by small carcinoma. This is due to their ability to secrete hormones which can directly affect the metabolic process in the body. Though some of these effects may be seen in other types of lung cancers they are not paraneoplastic syndromes.

1.Weakness

2.Seizures

3.Retention of fluid

4.Respiratory collapse

5.Coma

6.Vomiting

7.Nausea

8.Thick darkened skin around the neck and armpit.

These are a few of the many manifestations that can be caused by the hormonal secretions of small cell lung carcinoma.

PROGNOSIS

The outcome or survival of lung cancer patients is of topmost importance. Most people diagnosed with lung cancer normally have a survival rate of about 17% dating from 2007 to 2012. But this percentage of survival is dependent on certain key factors. These factors (prognostic factors are )

1.Cancer size.

2.Stage of cancer.

3.Type of cancer

4.General well being (performance status) of the patient .

In developed countries, the outcome of lung cancer is normally good since cancer is detected early. About 70% of people diagnosed with lung cancer survival in England for more than a year. This percentage is greatly reduced in developing countries where the diagnosis is made very late. The percentage of survival in a year in developing countries rank around 14%.

Generally, localized cancers have a good prognostic value of about 53% survival rate within five years. In contrast, Metastatic cancers have 4% five years rate of survival.

Small cell carcinomas which are normally detected at late stages and can not be removed by Surgery has a poor prognosis.

ROUTES OF METASTASIS

1.Direct invasion into nearby tissue.

2.Through blood vessels to distant organs.

3.Through lymphatic vessels.

STAGES OF LUNG CANCER

Lung Cancer staging is done using; Tumor size, Extent of lymph node invasions and metastasis of the cancer cells. The stage of cancer will determine the rate of survival and the type of treatment.

1.Stage 1A and 1B; Cancer Cell is in one lobe of the lung with no lymph node involvement. Size of the tumor is between 2 to 3cm.

 2.Stage 2 A and 2B; Tumor is in one lobe of the lung and has invaded nearby lymph nodes. Tumour size is between 3cm to 7cm.

 3.Stage 3A And 3B; Cancer Cells move to the opposite sides of the chest and affect other distant lymph nodes. Cancer cells still stay in the lung that they began forming from.

 4.Stage 4; Cancer Cells spread to both lobes of the lung and spread to distant organs.

DIAGNOSIS OF LUNG CANCER

1. Sputum examination under a microscope can reveal cancer cells.

2.Tissue biopsy

3.Bronchoscopy to observe the lung closely

4.Imaging techniques;

.Computed tomography (CT)

.Magnetic Resonance Imaging (MRI)

.Chets X-rays.

PREVENTION OF LUNG CANCER

1.Never smoke if you haven’t begun.

2. Quit smoking tobacco products.

3. Stop staying close to people when they are smoking tobacco products (avoid second-hand smoking).

4. Protective wears at work from asbestos and other carcinogens.

5. Exercise regularly.

6. Eat enough fruits and vegetables.

MANAGEMENT OF LUNG CANCER

1.Surgery; It normally works for Non-small cell carcinomas and on few occasions for non-small cell carcinoma if detected early. Some of the procedures are ;

A. Wedge resection; Cancerous cells are removed with a small part of immediate surrounding healthy tissue.

B.Resection of a segment; A large part or segment of the lung tissue is removed.

C.Lobectomy; Removal of the lobe affected by cancer.

D.Pneumonectomy; The two lobes of the lung are removed.

 2. Chemotherapy; Drugs are given before and after surgery to kill cancer cells and prevent recurrences.Example ;leurocristine,methotrexate.

 3.Radiation therapy; Use of amplified energy light rays to kill cancer cells.

 4. Targeted therapy; Drugs target specific characteristics in cancer cells. For Example specific alternations in genes to kill cancer cells. Examples of Drugs; Ceritinib, Afatinib.