Definition of Cancer

Cancer is a  large group of diseases that can start in almost any organ or tissue of the body when abnormal cells grow uncontrollably go beyond their usual boundaries to invade adjoining parts of the body and/or spread to other organs. This disease can originate in any part of the human body. Under normal circumstances, body cells undergo a process called cell division, where they grow and multiply to produce new cells when needed by the body. Cellular growth occurs in the nucleus through a unit called DNA. DNA is organized into separate units called genes within a cell, each of which contains a set of instructions that regulate the cell’s functions, including its growth and division. These instructions are essential for maintaining cellular homeostasis and preventing uncontrolled growth.


The Etiology of Cancer Cell Development

Alterations in the DNA of an individual cell or a cluster of healthy cells result in the cessation of their regular functioning and the emergence of abnormal or impaired growth. These modifications can occur either spontaneously during an individual’s lifetime, be inherited from previous generations, or be triggered by various environmental mutagenic agents. Consequently, the formation of anomalous cells leads to the development of tumors, which can either be cancerous or non-cancerous.

The Difference Between Cancer Cells and Normal Cells

Cancer cells and normal cells display differences at various levels. While some disparities are well-known, others have recently been discovered and are less familiar. The following table illustrates the differences between these two cell types:

Attributes Normal Cell Cancer Cell
Cell growth rate
Healthy cells undergo a regulated process of growth and division to replenish damaged or expired cells.
Cancer cells frequently exhibit rapid growth and a lack of differentiation, resulting in the formation of tumor masses.
Cellular longevity
Regular cells go through a process of maturation, have a typical lifespan, and undergo programmed cell death when they become old or encounter damage.
Cancerous cells exhibit an irregular lifespan and have the potential to proliferate uncontrollably, frequently metastasizing to other regions of the body.
Cell-to-cell communication
Normal cells exhibit a response to these signals and refrain from growing in the absence of necessity.
Cancerous cells exhibit a lack of response to signals from neighboring cells that typically indicate an overgrowth of cells.
Cell appearance
Normal cells have a regular shape
Cancer cells have an irregular shape.
Cellular repair
Normal cells either repair themselves or die when they are damaged or old.
Cancer cells do not repair or die.
Ability to metastasize (spread)
Normal cells stay in the area of the body where they belong.
Cancer cells have the ability to detach, and migrate to different regions of the body via the lymphatic system and bloodstream.
Immune escape
Damaged normal cells are identified and eliminated by the immune system.
Cancer cells possess the ability to deceive the immune system of the body sufficiently, leading to their transformation into a tumor.
Normal cells release certain substances that induce them to adhere to one another, forming a cohesive unit.
Due to their inability to produce certain substances, cancer cells have the tendency to spread to neighboring areas or even distant regions of the body via the bloodstream or lymphatic system.
Blood supply
Normal cells undergo angiogenesis as a natural part of their growth and development, as well as when there is a requirement for tissue repair due to damage.
Cancer cells stimulate angiogenesis even in the absence of growth necessity. Consequently, blood vessels proliferate irrespective of the cellular requirements, perpetually nourishing the tumor.

Lung Cancer

Cancer is a medical condition characterized by the uncontrolled multiplication of abnormal cells that can infiltrate and affect nearby tissues. This disease disrupts the normal regulation and balance of cell growth, leading to the excessive proliferation and division of cells, which eventually forms a mass known as a tumor. In the case of lung cancer, this abnormal pattern of cell growth occurs in the lung tissue. Lung cancer is the second most prevalent type of cancer worldwide. This disease arises when cancerous cells in the lung tissue start to divide uncontrollably, causing a reduction in the individual’s respiratory capacity. Typically, clinical symptoms manifest as the disease progresses or spreads to other parts of the body (metastasizes).

Risk Factors in Lung Cancer

There are various factors that can lead to the development of lung cancer, including smoking, secondhand smoker, inhalation of radon gas, asbestos, an unhealthy diet, radiation therapy, and exposure to other environmental or occupational substances. Additionally, family history can also play a role in the development of this disease.

Types of Lung Cancer

Lung cancer has the potential to impact various regions within the lung. However, in a broader sense, the term “lung cancer” is commonly used to refer to two primary types that exhibit distinct growth and spreading patterns and can be identified through microscopic examination. These two types are Small Cell Lung Carcinoma (SCLC) and Non-Small Cell Lung Carcinoma (NSCLC).

Non-Small Cell Lung Carcinoma (NSCLC)

Approximately 80% to 85% of lung cancers are classified as Non-Small Cell Lung Cancer (NSCLC). NSCLC encompasses various subtypes, namely adenocarcinoma, squamous cell carcinoma, and large cell carcinoma. These subgroups originate from distinct lung cell types, yet their treatment and prognosis often exhibit similarities.


Adenocarcinoma, the most prevalent form of Non-Small Cell Lung Cancer (NSCLC), originates from cells that typically produce substances like mucus. This particular type of lung cancer is primarily found in individuals who smoke or have a history of smoking, as well as Asians and those under the age of 45.

Typically, adenocarcinoma develops in the outer regions of the lungs, starting from the periphery and extending beneath the bronchial lining in glandular cells responsible for secretion.

Squamous Cell Carcinoma

Lung squamous cell carcinoma is the second most prevalent form of lung cancer following lung adenocarcinoma and exhibits a comparatively slower growth rate when compared to other lung cancer variants. Typically originating in the bronchi, which serves as conduits for air to reach the lungs, this particular cancer type shares a common association with smoking, akin to other forms of cancer.

Large Cell Carcinoma

Large cell carcinoma has the potential to manifest in any part of the lung, predominantly in the outer regions, and has a tendency to proliferate rapidly and spread more aggressively than other forms of lung cancer. This variant of lung cancer poses a greater challenge in terms of treatment compared to other types. The cancer cells in this type of carcinoma are notably larger in size, making them discernible when viewed under a microscope.

Small Cell Lung Cancer (SCLC)

Small Cell Lung Cancer (SCLC) accounts for approximately 15 to 20% of all lung cancers and exhibits a more aggressive growth and metastatic potential compared to Non-Small Cell Lung cancer (NSCLC). The heightened propensity of SCLC to spread to other parts of the body enhances its responsiveness to chemotherapy. Nevertheless, it is important to note that SCLC is generally less amenable to complete cure when compared to NSCLC. In certain instances, lung cancer tumors may encompass a combination of both NSCLC and SCLC subtypes.

Benign Lung Cancer

A pulmonary nodule is a compact and circular formation resulting from the anomalous proliferation of cells encompassing the healthy lung tissues. The identification and management of benign tumors can be accomplished through the examination of chest X-rays and CT scans. Benign lung tumor cells do not metastasize to distant body regions and pose minimal risk to one’s life. However, it is important to acknowledge that benign tumors may occasionally transform into malignant and cancerous growths over time. Consequently, it is imperative to administer appropriate treatment for benign tumors as well.

Causes of Benign Lung Tumors

Benign lung tumors are commonly characterized by an unclear etiology. However, they are frequently attributed to various factors, including:

  1. Infectious inflammations such as tuberculosis, lung abscess, infectious fungi, and pneumonia.
  2. Non-infectious inflammations like rheumatoid arthritis, Wegener’s granulomatosis, and sarcoidosis, as well as congenital anomalies like lung cysts or other abnormalities in the lungs.

What is Metastatic Lung Cancer?

Advanced or metastatic cancer refers to the progression of cancer originating from one lung to subsequently affect the other lung and various other regions within the body.

Stages of Lung Cancer

The determination of the stages of lung cancer is based on the extent of its spread and intensity. To determine the stage of cancer, diagnostic tests such as MRI, CT scan, and PET scan are utilized. The staging of lung cancer is crucial for doctors to devise an effective treatment plan.

Hidden Stage: Lung cancer remains undetectable on imaging scans, yet malignant cells can be found in the sputum and potentially disseminated to various regions within the body.

Stage 0:   The presence of abnormal cells is limited to the superficial layers of the airway lining cells.

Stage 1:    The tumor in the lung is smaller than 5 cm and has not yet spread to other areas of the body.

Stage 2:   The tumor is either smaller than 5 cm and has spread to the lymph nodes of the lung, or smaller than 7 cm and has only affected nearby tissues without involving the lymph nodes.

Stage 3:   The cancer has disseminated to additional regions of the lung, encompassing tissues, and lymph nodes.

Stage 4:  At this advanced stage, the cancer has metastasized and propagated to various areas of the body, including the bone or brain.

Lung Cancer Symptoms

In the initial stages of lung cancer, individuals may not exhibit any symptoms. The manifestation of lung cancer symptoms differs based on the origin of its spread within the lung, resembling some extent symptoms associated with a respiratory infection.

  1. Persistent coughing or the presence of blood in sputum that persists or deteriorates
  2. Chest pain that is exacerbated by deep breaths, coughing
  3. Change in voice and experiencing hoarseness
  4. Frequent occurrences of lung infections, such as bronchitis and pneumonia
  5. Swelling of lymph nodes in the chest area
  6. Loss of appetite and weight
  7. Feeling fatigued and lacking energy
  8. Difficulty in swallowing food
  9. Shortness of breath and wheezing

If left untreated, the patients may experience more pronounced symptoms, including but not limited to:

  1. Bone pain
  2. Changes in the nervous system, such as headaches, weakness or numbness in an arm or leg, dizziness, balance issues, or seizures due to the spread of cancer to the brain
  3. Developing jaundice, which is characterized by the yellowing of the skin and eyes, following the spread of the cancer to the liver
  4. Swelling of lymph nodes (a collection of immune system cells), such as the lymph nodes in the neck or above the collarbone

Lung Cancer Prevention

Lung cancer is predominantly caused by smoking, as evidenced by statistics and surveys which indicate that over 90 percent of lung cancer patients are tobacco users, particularly cigarette smokers. While genetic and hereditary factors may also contribute to the development of lung cancer, there is no definitive method for preventing the disease. However, it is possible to mitigate the risk of lung cancer by adopting certain lifestyle habits such as engaging in regular exercise, consuming a diet that is rich in vegetables, and abstaining from smoking.

Lung Cancer Treatment

  1. Surgery: surgery is often considered as the initial course of action for lung cancer treatment. Individuals with non-metastasized lung cancer are suitable candidates for surgery. The procedure typically entails the removal of a lobe or a significant portion of the lung, known as a lobectomy. In more severe instances, the surgeon may opt to remove the entire lung. However, the decision to proceed with this surgical intervention is contingent upon the overall health status of the individual.
  2. Radiation therapy: radiation therapy involves the use of high-energy beams (radio waves) to eliminate cancer cells, particularly NSCLC tumors, located on the outer regions of the lung. Typically, radiotherapy is administered prior to surgery to decrease the size of the tumor. This treatment modality is most effective in managing cancers that are localized and have not metastasized. The integration of chemotherapy and radiotherapy before and after surgery significantly enhances the efficacy of the treatment. Additionally, radiation therapy can be employed as palliative care to reduce tumor size and alleviate pain.
  3. Chemotherapy: chemotherapy is a treatment method that involves the use of multiple drugs to halt the growth or eliminate cancer cells. These drugs are specifically designed to target cells that are dividing rapidly, making it an effective option for cancer cells that have spread to other parts of the body. Typically, chemotherapy drugs are administered before or after surgery, or in conjunction with other types of medication.
  4. Targeted drug therapy: targeted drug therapy involves the use of drugs that possess specific characteristics tailored to the genetics of cancer cells. These drugs are designed to identify cancer cells by targeting genetic mutations, and unlike chemotherapy, they exclusively impact these cells without causing harm to healthy tissues in the body. Once the targeted therapy drugs locate cancer cells, they can facilitate the immune system in recognizing and combating cancer as a disease itself (immunotherapy), or directly engage with the proteins to eliminate the cancer cells. In the case of direct action, targeted therapy drugs can impede the transmission of messages that promote further growth and spread among cancer cells, or hinder the formation of blood vessels that supply nutrients to the cancerous tumor, thereby depriving the cells of the resources necessary for their growth.

Certain alterations (mutations) in genes have been observed in individuals with NSCLC, which facilitate the growth of cancerous cells in the lungs. These genetic mutations are responsible for the development of lung cancer and can be attributed to various genes such as:

  1. Epidermal Growth Factor Receptor (EGFR)
  2. Anaplastic Lymphoma Kinase (ALK)
  3. Receptor Tyrosine Kinase (ROS)

Genetic mutations are responsible for the unregulated proliferation of normal cells, ultimately resulting in the development of cancer and the formation of tumors. The primary objective of targeted therapy for lung cancer is to halt this progression, thereby impeding the continued growth of cancer cells and tumors. Various forms of targeted therapies are available for the treatment of lung cancer. Each drug utilized in the targeted treatment of lung cancer possesses both a brand name and a specific drug name. Medications employed in the targeted treatment of lung cancer encompass a range of options including:

  1. Afatinib (brand name Giotrif®)
  2. Alcitinib (brand name Alecenta®)
  3. Brigatinib (brand name Alunbrig®)
  4. Ceritinib (brand name Zykadia®)
  5. Crizotinib (brand name Xalkori®)
  6. Erlotinib (brand name Tarceva®)
  7. Gefitinib (brand name Iressa®)
  8. Nintedanib (brand name Vargatef®)
  9. Osimertinib (brand name Tagrisso®)

Tyrosine Kinase Inhibitors (TKIs) are a class of drugs that encompass all of these medications. They function by impeding specific chemical pathways that instruct cancer cells to proliferate, divide, and metastasize.

Gefitinib, Afatinib and Osimertinib are EGFR inhibitors and Afatinib, Alectinib, Crizotinib and Ceritinib are ALK inhibitors. Crizotinib is also a ROS1 inhibitor.

Nintedanib inhibits certain functions of adenocarcinoma cells. Following the initial round of chemotherapy, this medication is administered alongside docetaxel, a chemotherapy drug, to enhance its effectiveness.

Side Effects of Lung Cancer Treatment

The side effects of lung cancer treatment are contingent upon the specific type of treatment administered and encompass the subsequent symptoms:

Chemotherapy Targeted drug therapy Surgery Radiotherapy
Nausea, Vomiting, Diarrhea, Hair loss Fatigue, Mouth ulcers, Loss of sensation, Weakness or tingling (Neuropathy)
Fatigue, Itchy rash, Diarrhea, Nausea, Vomiting, Joint pain, Rare side effects (such as pneumonitis, colitis, hepatitis, etc.)
Shortness of breath, Cough, Pain, Fatigue, difficulty swallowing, dry, itchy or red skin, Nausea, Vomiting, Lung atelectasis, Pneumonia, Cardiac arrhythmia, Bronchopleural fistula
Fatigue, Shortness of breath, Cough, Chest wall pain