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Comprehensive Overview of Cancer: Types, Causes, Diagnosis, and Treatment

specially made for NEET students. Detailed presentation covering cancer biology, tumor types, metastasis, carcinogens, diagnostic methods, and treatment options including surgery, radiotherapy, and chemotherapy.

Health & Medicine◦
CANCER
INTRODUCTION • Cancer is a disease in which normal body cells lose control over their growth and division, resulting in the formation of an abnormal mass of cells called a tumor or neoplasm. These cells continue to divide uncontrollably, invade nearby tissues, and may spread to distant organs through blood or lymph (metastasis). • Normally, cell division is tightly regulated by genes controlling the cell cycle, DNA repair, and programmed cell death (apoptosis). Mutations in these genes cause uncontrolled proliferation, leading to cancer.
CONTACT INHIBITION • Contact inhibition is the property of normal cells by which they stop dividing after coming into contact with neighboring cells. • It regulates cell proliferation and maintains normal tissue architecture. • In cancer, mutations in growth-regulating genes cause loss of contact inhibition. • Consequently, cancer cells ignore inhibitory signals, continue dividing uncontrollably, form tumors, invade surrounding tissues, and may metastasize to distant organs. • Therefore, loss of contact inhibition is a characteristic feature and an important hallmark of cancer.
Types of Tumors (Neoplasms) 1. Benign Tumor (Benign Neoplasm) • A benign neoplasm is a non-cancerous tumor that remains localized and does not invade surrounding tissues. Characteristics • Slow-growing. • Cells are well-differentiated and resemble normal cells. • Usually enclosed by a fibrous capsule. • Do not invade adjacent tissues. • Do not metastasize (do not spread to distant organs). • Surgical removal is usually curative. • Rarely recur after complete removal. • Examples: Lipoma, Fibroma, Adenoma, Papilloma.
Types of Tumors (Neoplasms) 2. Malignant Tumor (Malignant Neoplasm) • A malignant neoplasm is a cancerous tumor characterized by uncontrolled cell proliferation, invasion of surrounding tissues, and the ability to metastasize. Characteristics • Rapid and uncontrolled growth. • Cells are poorly differentiated (anaplastic) and appear abnormal. • Usually not encapsulated. • Invade and destroy surrounding tissues. • Can metastasize through the bloodstream, lymphatic vessels, or body cavities to form secondary tumors. • High chance of recurrence after treatment. • Potentially life-threatening if untreated. • Examples: Carcinoma, Sarcoma, Leukemia, Lymphoma, Melanoma.
Metastasis Metastasis is the process by which malignant (cancerous) cells spread from the primary tumor to distant parts of the body through the blood, lymphatic vessels, or body cavities, forming secondary tumors. It is the most important feature of malignant neoplasms and the leading cause of cancer-related deaths. Steps of Metastasis • Local invasion – Cancer cells invade surrounding normal tissues. • Intravasation – Cancer cells enter blood or lymphatic vessels. • Circulation – Cells travel through the bloodstream or lymph. • Extravasation – Cells leave the vessels and enter distant tissues. • Colonization – Cells multiply and form a secondary (metastatic) tumor. Flow: Primary Tumor → Local Invasion → Blood/Lymph → Distant Organ → Secondary Tumor (Metastasis)
Causes of Cancer – Carcinogenic Agents • Carcinogenic Agents A carcinogen is any physical, chemical, or biological agent capable of causing permanent genetic damage that leads to the transformation of a normal cell into a cancer cell. Continuous exposure to carcinogens increases the risk of mutations, resulting in uncontrolled cell proliferation and the development of cancer. Based on their nature, carcinogens are classified into physical, chemical, and biological carcinogens.
1. Physical Carcinogens A. Ionizing Radiation Ionizing radiation possesses sufficient energy to damage cellular DNA and is one of the most important physical carcinogens. Common sources include X-rays, gamma rays, alpha particles, beta particles, neutrons, and radon gas. Exposure may occur during medical imaging, radiotherapy, nuclear accidents, or occupational settings. Long-term or excessive exposure increases the risk of several malignancies, particularly acute leukemia, thyroid carcinoma, breast carcinoma, lung carcinoma, and bone sarcoma.
1. Physical Carcinogens B. Ultraviolet (UV) Radiation Ultraviolet radiation from sunlight is another important physical carcinogen. It is classified into UVA, UVB, and UVC. Among these, UVB is the most carcinogenic because it is primarily responsible for DNA damage in skin cells. Excessive exposure to sunlight, especially without adequate protection, significantly increases the risk of basal cell carcinoma, squamous cell carcinoma, and malignant melanoma.
1. Physical Carcinogens C. Chronic Physical Irritation Long-standing physical irritation and repeated tissue injury can increase the risk of cancer by promoting continuous cell regeneration. Examples include chronic ulcers, old burn scars (Marjolin ulcer), chronic osteomyelitis sinus tracts, gallstones, and long-standing inflammatory lesions. Persistent irritation over many years may eventually result in malignant transformation.
2. Chemical Carcinogens • Chemical carcinogens are substances capable of inducing cancer after prolonged exposure. They may act directly or require metabolic activation within the body. Most human cancers are associated with environmental or occupational exposure to chemical carcinogens.
3. Biological Carcinogens • Biological carcinogens include viruses, bacteria, and parasites that contribute to cancer development through chronic infection and long- term cellular damage.
Detection and Diagnosis of Cancer 1. Biopsy and Histopathological Studies (Gold Standard) A biopsy is the removal of a small piece of tissue from a suspected tumor for microscopic examination. It is the gold standard for confirming cancer because it provides a definitive diagnosis. The tissue is processed, stained (usually with Hematoxylin and Eosin (H&E)), and examined under a microscope by a pathologist. Types of Biopsy • Incisional biopsy – Removal of a part of the tumor. • Excisional biopsy – Removal of the entire tumor. • Needle biopsy – Tissue obtained using a fine or core needle. • Endoscopic biopsy – Tissue collected during endoscopy.
2. Blood and Bone Marrow Tests A. Blood Tests • Blood tests help detect abnormalities associated with cancer and monitor disease progression. B. Bone Marrow Examination • Bone marrow aspiration and biopsy are performed to diagnose cancers affecting the bone marrow. Used for • Leukemia • Lymphoma • Multiple myeloma • Myelodysplastic syndromes The sample is examined microscopically for abnormal blood-forming cells.
3. Imaging Techniques • Imaging studies help determine the site, size, extent, and spread (metastasis) of cancer. A. X-ray • X-rays use ionizing radiation to visualize internal organs. Uses • Detect lung tumors • Detect bone tumors • Identify chest abnormalities B. Computed Tomography (CT Scan) • CT scan combines multiple X-ray images to produce detailed cross-sectional images. Uses • Determine tumor size • Detect lymph node involvement • Assess metastasis • Evaluate cancers of the brain, chest, abdomen, and pelvis
C. Magnetic Resonance Imaging (MRI) • MRI uses a strong magnetic field and radio waves to produce detailed images of soft tissues. Uses • Brain tumors • Spinal cord tumors • Soft tissue tumors • Liver tumors • Pelvic cancers
4. Detection Using Antibodies Against Cancer-Specific Antigens (Immunodiagnosis) • Cancer cells express tumor-associated antigens (TAAs) or tumor-specific antigens (TSAs) that can be detected using monoclonal antibodies. • These antibodies bind specifically to cancer cells, helping identify and classify tumors.
5. Techniques of Molecular Biology • Modern molecular biology techniques detect genetic mutations, chromosomal abnormalities, and altered gene expression, allowing early diagnosis and personalized treatment. A. Polymerase Chain Reaction (PCR) • PCR amplifies small amounts of DNA, making it possible to detect cancer-related genetic mutations. Uses • Detect inherited cancer mutations • Detect minimal residual disease • Identify oncogenic viruses B. Fluorescence In Situ Hybridization (FISH) • FISH uses fluorescent DNA probes to identify chromosomal abnormalities. Detects • Gene amplification • Gene deletion • Chromosomal translocation • Example: HER2 gene amplification in breast cancer.
C. DNA Sequencing / Next-Generation Sequencing (NGS) • DNA sequencing identifies mutations in cancer-related genes. • Uses • Mutation analysis • Precision medicine • Personalized cancer therapy D. Cytogenetic Analysis (Karyotyping) • Examines chromosome number and structure. Detects • Philadelphia chromosome (CML) • Chromosomal translocations • Deletions • Duplications E. Flow Cytometry • Flow cytometry identifies abnormal cells using fluorescent antibodies. Used for • Leukemia • Lymphoma • Multiple myeloma
Treatment of Cancer 1. Surgery • Surgery is the physical removal of the tumor and surrounding normal tissue. It is the oldest and most effective treatment for localized solid tumors. Advantages • Best treatment for localized cancers. • Immediate removal of cancer. • Can provide complete cure in early-stage cancers. Limitations • Not effective for metastatic cancers. • Risk of bleeding, infection, and anesthesia-related complications.
Treatment of Cancer 2. Radiation Therapy (Radiotherapy) • Radiation therapy uses high-energy ionizing radiation to destroy cancer cells by damaging their DNA and preventing cell division. Types A. External Beam Radiotherapy (EBRT) • Radiation is delivered from a machine outside the body. B. Internal Radiotherapy (Brachytherapy) • Radioactive material is placed inside or near the tumor. Advantages • Preserves organs. • Can treat tumors inaccessible to surgery. • Effective when combined with surgery or chemotherapy.
Treatment of Cancer 3. Chemotherapy • Chemotherapy is the use of anticancer (cytotoxic) drugs to destroy rapidly dividing cancer cells throughout the body. Common Drug Classes • Alkylating agents • Antimetabolites • Antitumor antibiotics • Mitotic inhibitors • Platinum compounds Advantages • Treats cancer cells throughout the body. • Effective against metastatic disease. • Can be combined with surgery and radiotherapy.
Treatment of Cancer 4. Immunotherapy • Immunotherapy is the treatment that stimulates or enhances the body's immune system to recognize and destroy cancer cells. • Unlike chemotherapy, immunotherapy specifically targets cancer cells by activating immune responses. Types A. Monoclonal Antibodies (mAbs) Laboratory-produced antibodies bind to specific antigens on cancer cells. B. Immune Checkpoint Inhibitors • These drugs block inhibitory proteins that prevent T cells from attacking cancer cells. C. CAR-T Cell Therapy • The patient's T cells are genetically modified to recognize cancer cells and then reinfused into the body.