AIM Concept Integration
3rd Year MBBS
Multisystem
3rd Year MBBS
Multisystem
Topic 19 — Anticancer Pharmacology and Principles of Cancer Chemotherapy
Connect the major drug mechanisms, treatment strategies, resistance patterns and characteristic toxicities for rapid revision.
1. THE TOPIC IN ONE CONNECTED FLOW
Anticancer therapy works by attacking processes that malignant cells need for continued growth. Cytotoxic drugs mainly interfere with DNA synthesis, DNA integrity or mitosis, while hormonal drugs reduce growth signals in hormone-dependent tumors. The same mechanisms that damage cancer cells also explain resistance, toxicity and the need for carefully planned treatment combinations.
Malignant Cell Proliferation
Rapid DNA synthesis and repeated cell division
→
Drug Target
DNA, nucleotide synthesis, microtubules or hormone signaling
→
Cellular Effect
DNA damage, blocked nucleotide formation or failed mitosis
→
Tumor Response
Reduced proliferation and increased malignant-cell death
→
Treatment Outcome
Tumor shrinkage, remission or suppression of residual disease
Cytotoxic pathway
Alkylating agents / cisplatin → DNA cross-linking → impaired replication
Antimetabolites → reduced nucleotide synthesis → S-phase inhibition
Vinca alkaloids → microtubule inhibition → mitotic arrest
Antimetabolites → reduced nucleotide synthesis → S-phase inhibition
Vinca alkaloids → microtubule inhibition → mitotic arrest
Hormonal pathway
Tamoxifen → estrogen receptor blockade → reduced breast-tumor stimulation
Flutamide / goserelin → reduced androgen effect → reduced prostate-tumor stimulation
Flutamide / goserelin → reduced androgen effect → reduced prostate-tumor stimulation
Important parallel outcome:
Normal rapidly dividing tissues are also injured
→
myelosuppression, mucositis, alopecia and gonadal toxicity
Normal rapidly dividing tissues are also injured
→
myelosuppression, mucositis, alopecia and gonadal toxicity
2. KEY CLINICAL CONNECTIONS
Resistance During Chemotherapy
Increased P-glycoprotein expression
→
increased drug efflux
→
reduced intracellular concentration
→
multidrug resistance.
→
increased drug efflux
→
reduced intracellular concentration
→
multidrug resistance.
Toxicity and Rescue
Methotrexate toxicity → leucovorin rescue
Cyclophosphamide → acrolein → hemorrhagic cystitis → mesna
Doxorubicin → cardiac free-radical injury → dexrazoxane
Cyclophosphamide → acrolein → hemorrhagic cystitis → mesna
Doxorubicin → cardiac free-radical injury → dexrazoxane
Timing of Chemotherapy
Before surgery → neoadjuvant → reduce tumor size
After surgery → adjuvant → destroy microscopic residual cells
After remission → maintenance → reduce relapse
After surgery → adjuvant → destroy microscopic residual cells
After remission → maintenance → reduce relapse
3. AIM HIGH-YIELD INTEGRATION REVIEW
⭐ Cell cycle-specific drugs act mainly in defined phases: antimetabolites → S phase, vinca alkaloids → M phase, bleomycin → mainly G2 phase.
⭐ Alkylating agents and cisplatin damage DNA → replication fails; cyclophosphamide additionally forms acrolein → bladder injury.
Methotrexate → dihydrofolate reductase inhibition → reduced tetrahydrofolate → impaired purine and thymidylate synthesis → reduced DNA synthesis.
6-Mercaptopurine / azathioprine + allopurinol → reduced xanthine oxidase-mediated breakdown → increased toxicity, especially bone marrow suppression.
⭐ Anthracyclines → DNA intercalation + topoisomerase II inhibition + free radicals → effective cytotoxicity but risk of cardiomyopathy.
Bleomycin → DNA strand breaks → pulmonary toxicity; relatively little marrow suppression helps distinguish it from many cytotoxic drugs.
Hormonal therapy targets tumor growth signals: tamoxifen → ER-positive breast cancer; flutamide and goserelin → androgen-dependent prostate cancer.
⭐ Combination chemotherapy uses drugs with different mechanisms → greater tumor-cell killing + reduced emergence of resistant clones, while overlapping toxicity must be limited.
AIM Exam Trap:
Vincristine and vinblastine both inhibit microtubule formation, but vincristine → prominent neurotoxicity, whereas vinblastine → prominent bone marrow suppression.
Vincristine and vinblastine both inhibit microtubule formation, but vincristine → prominent neurotoxicity, whereas vinblastine → prominent bone marrow suppression.