CBSE · Class 12 · Biology · Human Health and DiseasesDefine cancer. Differentiate between benign and malignant tumors. Describe the major causes of cancer (carcinogens), methods used for its detection and diagnosis, and the common treatment modalities.

Definition of Cancer\nCancer is an abnormal, uncontrolled, and continuous division of cells in the body leading to the formation of a mass of tissues called a tumor. Normal cells show a property called contact inhibition (inhibition of cell growth upon contact with adjacent cells), which is lost in cancer cells.

Benign Tumors vs. Malignant Tumors

• Benign Tumors:

  • Remain confined to their original location.
  • Do not spread to other body parts.
  • Cause little damage and grow slowly.

• Malignant Tumors:

  • Consist of proliferating mass of cells called neoplastic cells.
  • Invade and damage surrounding normal tissues.
  • Show metastasis: cancerous cells slough off from the primary site, travel through blood to distant organs, and establish new secondary tumors. Metastasis is the most feared property of malignant tumors.

Causes of Cancer (Carcinogens)\nTransformation of normal cells into cancerous cells is induced by physical, chemical, or biological agents called carcinogens:

1. Physical Agents: Ionizing radiations (X-rays, gamma rays) and non-ionizing radiations (UV rays) damage DNA leading to neoplastic transformation.
2. Chemical Agents: Chemicals present in tobacco smoke (cause lung cancer), dyes, and heavy metals.
3. Biological Agents: Oncogenic viruses carrying viral oncogenes, or activation of cellular oncogenes ($c\text{-onc}$) / proto-oncogenes in normal cells under specific conditions.

Detection and Diagnosis

1. Biopsy and Histopathological Studies: Microscopic examination of thin tissue sections.
2. Blood and Bone Marrow Tests: To detect increased cell counts (e.g., in leukemia).
3. Imaging Techniques: Radiography (X-rays), Computed Tomography (CT scan creates 3D images), and Magnetic Resonance Imaging (MRI uses strong magnetic fields for non-invasive diagnosis).
4. Monoclonal Antibodies: Used to detect cancer-specific antigens.

Treatment Modalities

1. Surgery: Surgical removal of the localized tumor mass.
2. Radiotherapy: Tumor cells are irradiated lethally while taking care of surrounding normal tissues.
3. Chemotherapy: Administration of chemotherapeutic drugs to kill cancer cells (side effects include hair loss and anemia).
4. Immunotherapy: Patients are given biological response modifiers such as $\alpha$-interferon to activate their immune system and destroy tumors.