Cancer is a collection of related diseases. In all types of cancer, some of the body’s cells begin to divide without stopping and spread into surrounding tissues.
Cancer can start almost anywhere in the human body, which is made up of trillions of cells. Normally, human cells grow and divide to form new cells as the body needs them. When cells grow old or become damaged, they die, and new cells take their place. In cancer, this orderly process breaks down, leading to the uncontrolled growth that characterizes the disease.
The Roots: DNA & Mutations
Cancer is a genetic disease—it is caused by changes to genes that control the way our cells function, especially how they grow and divide. These changes are called mutations.
Types of Genetic Changes
- Inherited Mutations: About 5% to 10% of cancers are caused by harmful genetic changes passed from parent to child. These are called germline mutations.
- Acquired Mutations: Most cancers occur over time due to DNA damage throughout life. This damage can happen because of internal errors during cell division or external factors like tobacco smoke, radiation, and UV rays.
- Driver Mutations: Not all DNA changes cause cancer. "Driver" mutations are the specific changes that push a cell toward becoming cancerous.
How Cancer Spreads (Metastasis)
A cancer that has spread from the place where it first started to another place in the body is called metastatic cancer. The process by which cancer cells spread to other parts of the body is called metastasis.
When observed under a microscope, metastatic cancer cells generally look the same as cells of the original cancer. For example, breast cancer that spreads to the lung is still breast cancer, not lung cancer, and is treated as metastatic breast cancer.
Growth & Survival
Malignant Tumors (Cancerous)
Malignant tumors can invade nearby tissues and spread to distant organs through the blood or lymphatic system.
- Have irregular borders and grow rapidly.
- Can shed cells that travel to other sites (metastasis).
- Often recur after being removed if not all cells are eliminated.
Benign Tumors (Non-Cancerous)
Benign tumors do not spread into nearby tissues or to other parts of the body.
- Usually have smooth, regular borders.
- Generally do not come back once removed.
- While not cancerous, some (like brain tumors) can be dangerous if they press on vital structures.
How Cancers are Named
Cancers are typically named after the organ or tissue where they start. For example, lung cancer starts in the lung. However, they are further classified by the type of cell they began in:
- • Carcinoma: Starts in epithelial cells (lining of organs).
- • Sarcoma: Starts in bone or soft tissues.
- • Leukemia: Starts in blood-forming tissue (bone marrow).
The Global Burden
Cancer is a leading cause of death worldwide, accounting for nearly 10 million deaths in 2020. In India, the burden is increasing due to aging populations and changing lifestyles.
~20M
New Cases Globally (2022)
1 in 9
Indians will develop cancer
30-50%
Cases are Preventable
Main Categories of Cancer
Carcinoma
The most common type (80-90% of cases). Formed by epithelial cells (skin or tissue lining organs like breast, lung, colon). Subtypes include Adenocarcinoma and Squamous Cell Carcinoma.
Sarcoma
Rare cancers forming in bone and soft tissues (muscle, fat, blood vessels, fibrous tissue). Osteosarcoma is the most common bone cancer.
Leukemia
'Liquid cancers' of the bone marrow's blood-forming tissues. They do not form solid tumors but produce abnormal white blood cells that crowd out health ones.
Lymphoma
Cancers of the lymphatic system (immune system). Two main types: Hodgkin lymphoma and Non-Hodgkin lymphoma.
Multiple Myeloma
Cancer of plasma cells (immune cells made in bone marrow). It causes cancer cells to accumulate in bone marrow, crowding out healthy blood cells.
Melanoma
The most dangerous form of skin cancer. It develops in melanocytes (pigment cells). While rare compared to basal/squamous cell carcinoma, it is far more likely to spread.
Brain & Spinal Cord
Tumors of the Central Nervous System. There are many types, often named after the specific cell type they start in (e.g., Astrocytomas).