Question
Classify cancer into its major types — carcinoma, sarcoma, lymphoma, and leukemia. What is the difference between benign and malignant tumours? How do oncogenes and tumour suppressor genes contribute to cancer?
(NEET + CBSE Class 12)
Solution — Step by Step
| Type | Tissue of origin | Examples |
|---|---|---|
| Carcinoma | Epithelial tissue (skin, lining of organs) | Breast cancer, lung cancer, skin cancer |
| Sarcoma | Connective tissue (bone, cartilage, muscle, fat) | Osteosarcoma (bone), liposarcoma (fat) |
| Lymphoma | Lymphatic tissue (lymph nodes) | Hodgkin’s lymphoma, Non-Hodgkin’s lymphoma |
| Leukemia | Blood-forming tissue (bone marrow) | ALL, AML, CLL, CML |
Carcinomas are the most common (~85% of all cancers), because epithelial cells divide frequently and are exposed to carcinogens.
| Feature | Benign | Malignant |
|---|---|---|
| Growth | Slow | Rapid, uncontrolled |
| Spread | Stays localised, enclosed in capsule | Invades nearby tissues, metastasises |
| Danger | Usually not life-threatening | Life-threatening |
| Cells | Well-differentiated, look like normal cells | Poorly differentiated, abnormal |
| Example | Wart, lipoma | Carcinoma, sarcoma |
Metastasis — when cancer cells break away, travel through blood/lymph, and start new tumours elsewhere — is what makes malignant cancer deadly.
Cancer involves two types of gene mutations:
-
Proto-oncogenes (normal genes promoting cell growth) mutate to become oncogenes — they become permanently “ON,” driving uncontrolled division. Think of it as a stuck accelerator.
-
Tumour suppressor genes (like p53 and Rb) normally put brakes on cell division. When they mutate and stop working, cells divide without checkpoints. Think of it as failed brakes.
Cancer typically requires mutations in BOTH types — accelerator stuck ON and brakes failed.
Cancer Type Classification Tree
flowchart TD
A["Cancer — uncontrolled cell growth"] --> B["Benign — localised, non-spreading"]
A --> C["Malignant — invasive, metastatic"]
C --> D["Carcinoma — epithelial origin (85%)"]
C --> E["Sarcoma — connective tissue"]
C --> F["Lymphoma — lymphatic tissue"]
C --> G["Leukemia — blood/bone marrow"]
D --> D1["Breast, lung, skin cancer"]
E --> E1["Bone, cartilage, fat cancer"]
F --> F1["Hodgkin's, Non-Hodgkin's"]
G --> G1["ALL, AML, CLL, CML"]
H["Genetic causes"] --> I["Oncogenes — accelerator stuck ON"]
H --> J["Tumour suppressor mutation — brakes failed"]Why This Works
Cancer classification by tissue type is critical because treatment depends on where the cancer started. Carcinomas respond differently to chemotherapy than sarcomas. Leukemia (blood cancer) does not form solid tumours, so it cannot be surgically removed — it requires chemotherapy.
The “accelerator and brake” analogy for oncogenes and tumour suppressors is the most effective way to understand cancer genetics for NEET.
Common Mistake
Students think all tumours are cancer. A benign tumour (like a wart or uterine fibroid) is NOT cancer — it does not spread. Only malignant tumours are cancer. The defining feature of cancer is metastasis — the ability to spread to distant sites. NEET tests: “What property distinguishes malignant from benign?” Answer: metastasis (not just uncontrolled growth, because benign tumours also grow).