Cancer
Cancer is a group of more than 100 diseases characterised by the uncontrolled growth and spread of abnormal cells in the body. It is one of the leading causes of death worldwide — affecting millions of people across every country, culture and age group. When the body's normal cell regulation breaks down, cells begin to divide uncontrollably, ignore signals to stop growing and may eventually invade surrounding tissues and spread to other parts of the body — a process known as metastasis. Cancer can arise in virtually any tissue or organ of the human body — giving rise to a vast range of cancer types, each with its own biology, behaviour, treatment and prognosis.
Overview
In a healthy human body, cells grow, divide and die in a carefully regulated, orderly process. This regulation is controlled by a complex network of genes, proteins and signalling pathways that tell cells when to grow, when to divide and when to die. Cancer begins when this regulation fails — typically due to mutations (changes) in the DNA of a single cell. Over time, these mutations accumulate, and the affected cell gains the ability to divide uncontrollably, evade the immune system and ultimately spread to other parts of the body.
Cancer is not one disease — it is many. More than 100 distinct types of cancer have been identified — classified according to the type of cell or tissue from which they originate. Each type of cancer has its own unique molecular profile, clinical behaviour and response to treatment — making cancer one of the most complex and challenging groups of diseases in medicine.
How Cancer Develops
Cancer develops through a multi-step process involving the accumulation of genetic and epigenetic changes in cells:
Initiation
Cancer begins when a cell acquires a mutation — a change in its DNA — that gives it a growth advantage over normal cells. This can be caused by environmental factors (such as tobacco, radiation or certain chemicals), infectious agents (such as certain viruses), inherited genetic mutations or random errors in DNA replication.
Promotion
The initiated cell begins to divide more rapidly than normal — producing a growing population of abnormal cells. At this stage, the changes are still relatively limited and the cells may not yet be fully cancerous.
Progression
As the abnormal cells continue to divide, they accumulate additional mutations — gradually acquiring more aggressive characteristics including the ability to invade surrounding tissues, form new blood vessels (angiogenesis) and spread to distant sites (metastasis). This is the stage at which a tumour becomes fully malignant.
Metastasis
Metastasis — the spread of cancer from its original site to other parts of the body — is the process responsible for the vast majority of cancer deaths. Cancer cells can enter the bloodstream or lymphatic system, travel to distant organs and establish new tumours at secondary sites — making the disease far more difficult to treat.
Types of Cancer
Cancer is classified according to the type of cell or tissue from which it originates:
Carcinomas
Carcinomas are cancers that arise from epithelial cells — the cells that line the surfaces of organs and tissues. They are the most common type of cancer — accounting for the majority of breast, lung, colorectal, prostate, stomach, liver and cervical cancers.
Sarcomas
Sarcomas are cancers that arise from connective tissues — including bone, muscle, fat, blood vessels and cartilage. They are relatively rare but can be highly aggressive.
Leukaemias
Leukaemias are cancers of the blood — arising in the bone marrow and affecting the production of blood cells. They are characterised by the overproduction of abnormal white blood cells.
Lymphomas
Lymphomas are cancers of the lymphatic system — including Hodgkin lymphoma and non-Hodgkin lymphoma. They arise from lymphocytes — a type of white blood cell — and can affect lymph nodes, the spleen and other lymphatic tissues.
Brain and Central Nervous System Cancers
Cancers of the brain and central nervous system include gliomas, meningiomas and glioblastomas — among the most difficult cancers to treat due to their location and biology.
Other Types
Other major cancer types include:
- Breast Cancer — One of the most common cancers worldwide, affecting both women and men
- Lung Cancer — The leading cause of cancer death globally
- Colorectal Cancer — Affecting the colon and rectum
- Prostate Cancer — The most common cancer in men in many countries
- Cervical and Ovarian Cancer — Affecting the female reproductive system
- Liver Cancer — Often associated with hepatitis infection and cirrhosis
- Pancreatic Cancer — One of the most difficult cancers to detect and treat
- Skin Cancer — Including melanoma and non-melanoma skin cancers
Causes and Risk Factors
Cancer arises from a complex interaction of genetic, environmental and lifestyle factors:
Genetic Factors
Some cancers are caused by inherited gene mutations — including mutations in BRCA1 and BRCA2 (associated with breast and ovarian cancer) and mutations in genes such as APC (associated with colorectal cancer). People with a family history of certain cancers may have an elevated risk.
Environmental and Lifestyle Factors
- Tobacco — The single largest preventable cause of cancer — responsible for lung, throat, mouth, oesophagus, stomach, kidney and bladder cancers
- Alcohol — Associated with cancers of the liver, breast, colorectum and oesophagus
- Radiation — Ultraviolet radiation from the sun increases the risk of skin cancer; ionising radiation increases the risk of leukaemia and other cancers
- Diet and Obesity — A diet high in processed foods and red meat and low in fruits and vegetables is associated with increased cancer risk; obesity is a significant risk factor for multiple cancers
- Physical Inactivity — Associated with increased risk of colon, breast and endometrial cancers
- Occupational Exposures — Exposure to carcinogens such as asbestos, benzene, formaldehyde and certain chemicals in the workplace
Infectious Agents
- Human Papillomavirus (HPV) — Causes cervical cancer and other cancers
- Hepatitis B and C — Associated with liver cancer
- Helicobacter pylori — Associated with stomach cancer
- Epstein-Barr Virus — Associated with certain lymphomas
Symptoms
Cancer symptoms vary widely depending on the type and location of the cancer. Common warning signs include:
- Unexplained weight loss
- Fatigue and weakness
- Persistent pain
- Skin changes — including new or changing moles
- Changes in bowel or bladder habits
- Unusual bleeding or discharge
- A lump or thickening in the breast or elsewhere
- Difficulty swallowing
- Persistent cough or hoarseness
Early detection is critical — many cancers are highly treatable when detected at an early stage.
Diagnosis
Cancer is diagnosed through a range of methods including:
- Biopsy — The removal and examination of a tissue sample — the definitive method for diagnosing cancer
- Imaging — X-ray, CT scan, MRI, PET scan and ultrasound — used to detect tumours and assess their extent
- Blood Tests — Including tumour markers such as PSA (for prostate cancer) and CA-125 (for ovarian cancer)
- Endoscopy — Direct visualisation of internal organs using a camera
- Genetic Testing — Identifying inherited gene mutations that increase cancer risk
Treatment
Cancer treatment has advanced dramatically in recent decades — with a growing range of effective therapies:
Surgery
Surgical removal of tumours remains one of the most important cancer treatments — particularly for solid tumours that have not spread to other parts of the body.
Chemotherapy
Chemotherapy uses drugs that kill rapidly dividing cells — affecting cancer cells throughout the body. It is used to treat many types of cancer and is often used in combination with other treatments.
Radiation Therapy
High-energy radiation is used to damage the DNA of cancer cells — preventing them from dividing. It can be delivered externally or internally (brachytherapy).
Targeted Therapy
Targeted therapies are drugs designed to attack specific molecular targets in cancer cells — such as specific proteins or gene mutations — with greater precision than conventional chemotherapy.
Immunotherapy
Immunotherapy harnesses the body's own immune system to recognise and destroy cancer cells. It includes immune checkpoint inhibitors, CAR-T cell therapy and cancer vaccines — and has transformed the treatment of several cancers.
Hormone Therapy
Hormone therapy blocks or reduces the levels of hormones that fuel certain cancers — particularly breast and prostate cancers.
Bone Marrow Transplant
Used primarily in leukaemia and lymphoma — replacing diseased bone marrow with healthy marrow to restore normal blood cell production.
Cancer in India
India faces a significant and growing cancer burden — with an estimated 1.4 million new cancer cases diagnosed every year. The most common cancers in India include breast cancer, cervical cancer, oral cancer, lung cancer and colorectal cancer. India has a growing network of cancer research and treatment institutions — including the Tata Memorial Centre (Mumbai), All India Institute of Medical Sciences (AIIMS) (New Delhi), Regional Cancer Centres across the country and numerous university research departments.
Indian scientists — supported by ICMR (Indian Council of Medical Research) and UGC (University Grants Commission) fellowships — are making important contributions to global cancer research — both within India and at leading international institutions around the world.
Prevention
Many cancers are preventable through lifestyle changes and vaccination:
- Quit Smoking — The single most important step in cancer prevention
- Limit Alcohol — Reducing alcohol consumption lowers cancer risk
- Maintain a Healthy Weight — Through diet and regular physical activity
- Sun Protection — Using sunscreen and protective clothing to reduce skin cancer risk
- Vaccination — HPV vaccine (prevents cervical cancer); Hepatitis B vaccine (prevents liver cancer)
- Regular Screening — Mammography, colonoscopy, Pap smear and other screening tests for early detection
- Healthy Diet — Rich in fruits, vegetables, whole grains and low in processed and red meat