AIM • STEP 10
Student Memory Support
Topic 17 — Molecular Basis of Cancer and Carcinogenesis
3rd Year MBBS • Multisystem • High-yield memory reinforcement and last-minute revision
1. High-Yield Flashcards
Tap each question to reveal the answer.
What is a proto-oncogene?
A normal cellular gene that promotes regulated growth, proliferation or survival.
What is an oncogene?
An abnormally activated growth-promoting gene derived from a proto-oncogene.
What is an oncoprotein?
The abnormal protein product of an activated oncogene that promotes growth or survival.
Which major genetic lesions can activate or disrupt cancer-related genes?
Point mutation, chromosomal translocation, gene amplification, deletion and abnormal chromosome structure or number.
How does gene amplification promote carcinogenesis?
It increases gene copy number, causing excessive production of a growth-promoting protein.
What is the main protective role of p53 after DNA damage?
It arrests the cell cycle for repair and promotes senescence or apoptosis if damage is irreparable.
What is meant by sustained proliferative signaling?
Cancer cells maintain growth signals that allow continued cell division despite normal regulatory controls.
What is tumor heterogeneity?
The presence of genetically and biologically different subclones within the same tumor.
What is initiation in chemical carcinogenesis?
Permanent, heritable DNA damage produced by a carcinogenic agent.
What is promotion in carcinogenesis?
Stimulation of proliferation of previously initiated cells without directly producing the initiating mutation.
How do indirect-acting chemical carcinogens become carcinogenic?
They undergo metabolic activation to form reactive electrophilic metabolites that damage DNA.
What characteristic DNA injury is associated with ultraviolet radiation?
Pyrimidine dimer formation.
How does ionizing radiation promote cancer?
It produces DNA strand breaks directly and through reactive oxygen species.
How do high-risk HPV proteins promote malignant transformation?
E6 impairs p53 function and E7 interferes with RB-mediated growth control.
How can Helicobacter pylori contribute to gastric cancer?
Chronic gastritis causes repeated injury and regeneration, promoting accumulation of genetic abnormalities.
Which bacterium is associated with gastric MALT lymphoma through chronic antigenic stimulation?
Helicobacter pylori.
What is the immediate priority in management of an acutely poisoned patient?
Stabilization of airway, breathing and circulation before toxin-specific management.
2. Mnemonics
Mnemonic Title: Major Genetic Targets in Cancer
GRAD
Meaning: Growth-promoting proto-oncogenes, growth Restraining tumor suppressors, Apoptosis-regulating genes, DNA repair genes.
Mnemonic Title: Proto-Oncogene Activation
PAG
Meaning: Point mutation, gene Amplification, chromosomal translocation affecting a Growth-promoting gene.
Mnemonic Title: Immediate Poisoning Priorities
ABC
Meaning: Airway → Breathing → Circulation before detailed toxin identification.
3. Memory Tables
Direct-Acting vs Indirect-Acting Chemical Carcinogens
| Feature | Direct-Acting | Indirect-Acting |
|---|---|---|
| Metabolic activation | Not required | Required |
| Reactive form | Original compound | Reactive metabolite |
| Core effect | Direct DNA injury | Metabolism → DNA injury |
Initiation vs Promotion
| Feature | Initiation | Promotion |
|---|---|---|
| Main event | Permanent DNA damage | Expansion of initiated cells |
| Direct mutagenic effect | Present | Not required |
| Memory clue | Creates the altered clone | Expands the altered clone |
4. Rapid Revision Points — Last-Minute Revision
- Cancer is a multistep genetic disease involving accumulated abnormalities in growth and survival pathways.
- Proto-oncogene activation produces a gain of growth-promoting function.
- Tumor suppressor loss removes normal restraints on proliferation.
- DNA repair defects promote genomic instability by allowing mutations to accumulate.
- p53 gives damaged cells time to repair DNA and removes severely damaged cells by apoptosis or senescence.
- Tumor heterogeneity results from progressive genetic changes in different subclones.
- Direct carcinogens act without metabolic activation; procarcinogens require conversion to reactive metabolites.
- UV radiation produces pyrimidine DNA lesions; ionizing radiation causes strand breaks and reactive oxygen injury.
- High-risk HPV promotes carcinogenesis through E6–p53 and E7–RB pathway disruption.
- HBV, HCV and H. pylori can promote cancer through persistent injury, inflammation and repeated regeneration.
- In suspected poisoning, life-threatening physiological problems are treated before exact toxin identification.
KMU Exam Trap: Initiation produces permanent genetic damage; promotion mainly increases proliferation of already initiated cells.
5. Clinical Memory Hooks
Breast carcinoma with excessive HER2 receptor production
→
gene amplification causing excessive growth signaling
→
gene amplification causing excessive growth signaling
High-risk HPV infection with cervical neoplasia
→
E6 impairs p53 and E7 interferes with RB
→
E6 impairs p53 and E7 interferes with RB
Long-standing hepatitis with later hepatocellular carcinoma
→
chronic injury and repeated regeneration promote genetic damage
→
chronic injury and repeated regeneration promote genetic damage
Chronic H. pylori infection with gastric MALT lymphoma
→
prolonged antigenic stimulation of B cells
→
prolonged antigenic stimulation of B cells
Unconscious patient after unknown ingestion
→
stabilize ABC and check immediately reversible problems before toxin-specific treatment
→
stabilize ABC and check immediately reversible problems before toxin-specific treatment
6. Starred High-Yield Exam Points
- ⭐ Proto-oncogene activation is a gain-of-function event; oncogenes produce growth-promoting oncoproteins.
- ⭐ p53 responds to DNA damage by cell-cycle arrest, repair, senescence or apoptosis.
- ⭐ Initiation = permanent heritable DNA injury; promotion = proliferation of initiated cells.
- ⭐ Indirect carcinogens require metabolic activation to reactive electrophilic metabolites capable of damaging DNA.
- ⭐ High-risk HPV: E6 impairs p53; E7 interferes with RB-mediated growth control.
- ⭐ H. pylori contributes to gastric adenocarcinoma through chronic inflammation and to MALT lymphoma through chronic B-cell stimulation.
- ⭐ Suspected poisoning: airway, breathing and circulation take priority over exact poison identification.