Anticancer Drugs — MCQs

Anticancer Drugs Indian Medical PG Practice Questions and MCQs

Question 221: Which of the following is an antimetabolite?

A. Cyclosporine
B. Methotrexate (Correct Answer)
C. Etoposide
D. Vinblastine

Explanation: **Explanation:** **1. Why Methotrexate is correct:** Methotrexate is a classic **antimetabolite** that acts as a structural analogue of folic acid. It competitively inhibits the enzyme **Dihydrofolate Reductase (DHFR)**. This inhibition prevents the conversion of dihydrofolate to tetrahydrofolate (THF), which is essential for the synthesis of thymidylate and purines. By disrupting DNA and RNA synthesis, it primarily acts during the **S-phase** of the cell cycle. **2. Why the other options are incorrect:** * **Cyclosporine (A):** This is an **immunosuppressant** (calcineurin inhibitor), not a cytotoxic anticancer drug. It is primarily used to prevent graft rejection and in autoimmune diseases. * **Etoposide (C):** This is a plant derivative (epipodophyllotoxin) that acts as a **Topoisomerase II inhibitor**, leading to DNA strand breaks. * **Vinblastine (D):** This is a **Vinca alkaloid** that acts as a microtubule inhibitor. It binds to tubulin and prevents polymerization, causing mitotic arrest in the **M-phase**. **Clinical Pearls for NEET-PG:** * **Rescue Therapy:** Leucovorin (folinic acid) is used as "Leucovorin Rescue" to bypass DHFR inhibition and protect normal cells from methotrexate toxicity. * **Adverse Effects:** Methotrexate can cause myelosuppression, mucositis, and hepatotoxicity (cirrhosis with long-term use). * **Antimetabolite Sub-groups:** Remember other antimetabolites include Purine analogues (6-MP, 6-TG) and Pyrimidine analogues (5-FU, Cytarabine). * **Resistance:** Resistance to Methotrexate often occurs due to decreased drug uptake or increased DHFR enzyme production.

Question 222: What is the mechanism of action of imatinib mesylate?

A. Increases the metabolism of P-glycoprotein.
B. Blocks the action of P-glycoprotein.
C. Blocks the action of the chimeric fusion protein BCR-ABL. (Correct Answer)
D. Non-competitive inhibition of the ATP binding site.

Explanation: **Explanation:** **1. Why Option C is Correct:** Imatinib mesylate is a revolutionary targeted therapy known as a **selective tyrosine kinase inhibitor (TKI)**. It specifically targets the **BCR-ABL** tyrosine kinase, a chimeric fusion protein resulting from the **Philadelphia chromosome (t[9;22])**. In Chronic Myeloid Leukemia (CML), this protein is constitutively active, leading to uncontrolled cell proliferation. Imatinib works by acting as a **competitive inhibitor at the ATP-binding site** of the BCR-ABL enzyme, preventing the phosphorylation of substrates and effectively "turning off" the oncogenic signal. **2. Why Other Options are Incorrect:** * **Options A & B:** P-glycoprotein (P-gp) is an efflux pump associated with multi-drug resistance (MDR) in cancer cells. While Imatinib is a substrate for P-gp (which can lead to drug resistance), its primary therapeutic mechanism of action is not the modulation of this protein. * **Option D:** Imatinib is a **competitive** inhibitor, not a non-competitive one. It competes directly with ATP for the binding pocket on the kinase domain. **3. NEET-PG High-Yield Clinical Pearls:** * **Drug of Choice (DOC):** Imatinib is the first-line treatment for **Chronic Myeloid Leukemia (CML)** and **Gastrointestinal Stromal Tumors (GIST)**. * **GIST Mechanism:** In GIST, it inhibits the **c-KIT (CD117)** tyrosine kinase. * **Other Targets:** It also inhibits the Platelet-Derived Growth Factor Receptor (**PDGFR**). * **Side Effects:** The most characteristic side effect is **periorbital edema** (fluid retention). Others include nausea, muscle cramps, and diarrhea. * **Resistance:** Resistance often develops due to point mutations in the BCR-ABL kinase domain (e.g., **T315I mutation**), which may require second-generation TKIs like **Dasatinib** or **Nilotinib**.

Question 223: Citrovorum factor is given along with which of the following drugs?

A. Methotrexate
B. Pemetrexed
C. Pyrimethamine
D. Cytosine arabinoside (Correct Answer)

Explanation: **Explanation** **Citrovorum factor**, also known as **Leucovorin** or Folinic acid, is a reduced form of folic acid. Its primary clinical utility is to provide a source of folate that bypasses the enzyme **Dihydrofolate Reductase (DHFR)**. **Why the Options are Challenging:** In clinical practice, Leucovorin is most famously used as **"Leucovorin Rescue"** to prevent toxicity from high-dose **Methotrexate (Option A)**. It is also used to enhance the efficacy of 5-Fluorouracil and to reduce the toxicity of **Pemetrexed (Option B)** and **Pyrimethamine (Option C)**. All three of these drugs interfere with the folate pathway. **The Correct Answer (Context of the Question):** In the context of standard pharmacological teaching and competitive exams like NEET-PG, Citrovorum factor is **NOT** used with **Cytosine arabinoside (Cytarabine)**. Cytarabine is a pyrimidine antimetabolite that inhibits DNA polymerase; it has no interaction with the folate pathway. Therefore, if the question asks which drug it is given with and marks Cytarabine as the "correct" choice in a "Except" style or specific clinical mismatch, it usually indicates a distracter or a specific test-bank error. *Note: In most standard medical literature, Citrovorum factor is indicated for A, B, and C. If this question appeared as "is given with... EXCEPT," then D would be the correct answer.* **Incorrect Options Breakdown:** * **Methotrexate:** Inhibits DHFR. Leucovorin bypasses this block to protect normal cells (Rescue). * **Pemetrexed:** A multi-targeted antifolate; Leucovorin/Folic acid is mandatory to reduce hematologic and GI toxicity. * **Pyrimethamine:** An antiprotozoal that inhibits DHFR; Leucovorin is given to prevent megaloblastic anemia. **High-Yield Clinical Pearls:** 1. **Leucovorin Rescue:** Started 24 hours after Methotrexate to prevent bone marrow suppression. 2. **5-FU Interaction:** Unlike with Methotrexate, Leucovorin **increases** the toxicity and efficacy of 5-FU by stabilizing the binding of dUMP to thymidylate synthase. 3. **Levoleucovorin:** The active L-isomer of leucovorin, requiring half the dose.

Question 224: High dose Methotrexate is used for the treatment of which of the following conditions?

A. Osteosarcoma (Correct Answer)
B. Rhabdomyosarcoma
C. Retinoblastoma
D. Ewing's sarcoma

Explanation: **Explanation:** **Methotrexate (MTX)** is a folate antagonist that inhibits the enzyme **dihydrofolate reductase (DHFR)**, leading to a depletion of intracellular folate pools and inhibition of DNA synthesis. **Why Osteosarcoma is correct:** High-dose Methotrexate (HDMTX), typically defined as doses >500 mg/m², is a cornerstone in the treatment of **Osteosarcoma**. Because osteosarcoma cells often have poor drug uptake or high levels of DHFR, massive doses are required to create a concentration gradient sufficient to bypass resistance mechanisms. This regimen necessitates **Leucovorin Rescue** (Folinic acid) to protect healthy cells from lethal hematological and GI toxicity. **Why other options are incorrect:** * **Rhabdomyosarcoma:** Primarily treated with the **VAC regimen** (Vincristine, Actinomycin-D, and Cyclophosphamide). * **Retinoblastoma:** Management usually involves local therapy or systemic chemotherapy using **VEC** (Vincristine, Etoposide, and Carboplatin). * **Ewing’s Sarcoma:** The standard protocol is the **VDC/IE regimen** (Vincristine, Doxorubicin, Cyclophosphamide alternating with Ifosfamide and Etoposide). **High-Yield Clinical Pearls for NEET-PG:** 1. **Leucovorin Rescue:** Must be started 24 hours after MTX to provide an alternative source of reduced folate for normal cells. 2. **Hydration & Alkalinization:** To prevent **nephrotoxicity** (MTX precipitates in acidic urine), patients must be hydrated and given sodium bicarbonate to keep urine pH >7.0. 3. **Glucarpidase:** An enzyme used as an antidote for MTX toxicity in patients with renal failure. 4. **Resistance:** Occurs via decreased polyglutamation, decreased uptake (reduced folate carrier), or gene amplification of DHFR.

Question 225: Imatinib mesylate is used in the treatment of which of the following conditions?

A. Gastrointestinal stromal tumor (GIST) (Correct Answer)
B. Seminoma
C. MALT lymphoma
D. Zollinger-Ellison syndrome

Explanation: **Explanation:** **Imatinib mesylate** is a revolutionary targeted therapy that acts as a selective **tyrosine kinase inhibitor**. Its primary mechanism involves inhibiting the BCR-ABL fusion protein (the product of the Philadelphia chromosome), as well as the **c-KIT (CD117)** and PDGFR tyrosine kinases. 1. **Why Option A is Correct:** **Gastrointestinal Stromal Tumors (GIST)** are characterized by the overexpression of the **c-KIT receptor tyrosine kinase**. Imatinib binds to the ATP-binding site of the c-KIT enzyme, inhibiting downstream signaling that leads to tumor cell proliferation. It is the first-line medical treatment for unresectable or metastatic GIST. 2. **Analysis of Incorrect Options:** * **B. Seminoma:** While some seminomas express c-KIT, the standard of care remains surgery followed by radiotherapy or platinum-based chemotherapy (BEP regimen), not Imatinib. * **C. MALT Lymphoma:** This is a B-cell lymphoma often associated with *H. pylori* infection. Treatment involves antibiotic eradication of *H. pylori* or rituximab-based immunotherapy. * **D. Zollinger-Ellison Syndrome:** This is a gastrin-secreting neuroendocrine tumor. Management involves Proton Pump Inhibitors (PPIs) and surgical resection, not tyrosine kinase inhibitors. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Imatinib is the DOC for **Chronic Myeloid Leukemia (CML)**. * **Mechanism:** Competitive inhibition of the ATP-binding site. * **Side Effects:** The most characteristic side effect is **periorbital edema** (fluid retention). * **Resistance:** Resistance to Imatinib in CML often occurs due to mutations in the BCR-ABL kinase domain (e.g., T315I mutation), where **Ponatinib** is used.

Question 226: What is the primary effect of tamoxifen?

A. Increased risk of endometrial carcinoma (Correct Answer)
B. Decreased risk of ovarian cancer
C. Causes cardiotoxicity
D. Increased risk of osteoporosis

Explanation: **Explanation:** Tamoxifen is a **Selective Estrogen Receptor Modulator (SERM)**. Its primary mechanism involves acting as a competitive antagonist at estrogen receptors in breast tissue, making it a cornerstone in the treatment of hormone receptor-positive breast cancer. **1. Why Option A is correct:** The "selective" nature of Tamoxifen means it acts as an **agonist** (estrogen-like effect) in certain tissues, specifically the **uterus** and bone. By stimulating the estrogen receptors in the endometrium, it promotes endometrial hyperplasia, which significantly increases the risk of **endometrial carcinoma**. This is a classic high-yield association for medical exams. **2. Why the other options are incorrect:** * **Option B:** Tamoxifen does not significantly decrease the risk of ovarian cancer; its primary protective role is in breast tissue. * **Option C:** Cardiotoxicity is a hallmark side effect of **Anthracyclines** (e.g., Doxorubicin) and **Trastuzumab**, not Tamoxifen. Tamoxifen is actually associated with a slightly increased risk of thromboembolism (DVT/PE). * **Option D:** Because Tamoxifen acts as an **agonist in bone**, it increases bone mineral density and actually **decreases the risk of osteoporosis** in postmenopausal women. **NEET-PG High-Yield Pearls:** * **Drug of Choice:** Tamoxifen is the DOC for breast cancer in **premenopausal** women. (Aromatase inhibitors are preferred in postmenopausal women). * **Side Effects:** Hot flashes (most common), venous thromboembolism, and endometrial cancer. * **Raloxifene:** Another SERM that is an antagonist in both breast and uterus; therefore, it does **not** increase the risk of endometrial cancer but is used primarily for osteoporosis.

Question 227: Thalidomide is used in which of the following conditions?

A. Multiple myeloma (Correct Answer)
B. Squamous cell carcinoma
C. Basal cell carcinoma
D. Nasopharyngeal carcinoma

Explanation: **Explanation:** **Thalidomide** is a potent immunomodulatory and anti-angiogenic drug. Its primary mechanism in oncology involves inhibiting **Tumor Necrosis Factor-alpha (TNF-α)**, reducing IL-6 levels, and inhibiting vascular endothelial growth factor (VEGF), which prevents the blood supply to tumor cells. 1. **Why Multiple Myeloma is Correct:** Multiple myeloma (MM) cells are highly dependent on the bone marrow microenvironment and cytokines like IL-6 for survival. Thalidomide (and its derivatives, Lenalidomide and Pomalidomide) disrupts this environment and induces apoptosis in malignant plasma cells. It is a cornerstone of treatment for both newly diagnosed and relapsed/refractory MM, often used in combination with dexamethasone and bortezomib. 2. **Why Other Options are Incorrect:** * **Squamous, Basal, and Nasopharyngeal Carcinomas:** These are solid tumors of epithelial origin. The standard of care for these typically involves surgery, radiotherapy, or cytotoxic chemotherapeutic agents (like Cisplatin or 5-Fluorouracil) and targeted therapies (like Cetuximab). Thalidomide has not shown significant clinical efficacy in these specific malignancies. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Action:** Binds to the protein **Cereblon**, part of an E3 ubiquitin ligase complex, leading to the degradation of transcription factors (IKZF1/3) essential for myeloma cell survival. * **Teratogenicity:** Infamously causes **Phocomelia** (seal-like limbs). It is a Category X drug and requires strict contraceptive measures (STEPS program). * **Other Uses:** Erythema Nodosum Leprosum (ENL), HIV-associated wasting, and Aphthous ulcers. * **Side Effects:** Peripheral neuropathy, sedation, and increased risk of venous thromboembolism (VTE).

Question 228: What is the primary treatment for Chronic Myeloid Leukemia (CML)?

A. Vincristine
B. Imatinib (Correct Answer)
C. Cyclophosphamide
D. Methotrexate

Explanation: **Explanation:** **Correct Answer: B. Imatinib** The hallmark of Chronic Myeloid Leukemia (CML) is the **Philadelphia chromosome [t(9;22)]**, which creates the **BCR-ABL fusion gene**. This gene encodes a constitutively active **Tyrosine Kinase** protein that drives uncontrolled cellular proliferation. **Imatinib** is a 2-phenylaminopyrimidine derivative that acts as a selective **Tyrosine Kinase Inhibitor (TKI)**. It works by binding to the ATP-binding site of the BCR-ABL enzyme, effectively "turning off" the proliferative signal. It is the first-line standard of care for CML. **Incorrect Options:** * **A. Vincristine:** A Vinca alkaloid that inhibits microtubule polymerization (M-phase specific). It is primarily used in Acute Lymphoblastic Leukemia (ALL) and lymphomas, not as a primary treatment for CML. * **C. Cyclophosphamide:** An alkylating agent (nitrogen mustard) that causes DNA cross-linking. While used in many regimens (like CHOP for lymphoma), it is not a targeted therapy for CML. * **D. Methotrexate:** An antimetabolite that inhibits Dihydrofolate Reductase (DHFR). It is used in various cancers and autoimmune conditions but does not target the molecular driver of CML. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Resistance:** The most common cause of Imatinib resistance is a point mutation in the BCR-ABL kinase domain (specifically the **T315I mutation**). * **Next-Gen TKIs:** Dasatinib and Nilotinib are used if Imatinib fails. **Ponatinib** is specifically used for the T315I mutation. * **Side Effects:** Imatinib is known for causing **periorbital edema** and fluid retention. * **Monitoring:** Treatment response is monitored via Quantitative RT-PCR for BCR-ABL transcripts.

Question 229: Which of the following agents inhibits microtubule formation?

A. Paclitaxel
B. Vincristine (Correct Answer)
C. Etoposide
D. Irinotecan

Explanation: **Explanation:** The correct answer is **Vincristine**. This question tests your understanding of drugs acting on the mitotic spindle (M-phase of the cell cycle). **1. Why Vincristine is Correct:** Vincristine belongs to the **Vinca Alkaloids** (derived from *Catharanthus roseus*). Its mechanism of action involves binding to **tubulin dimers**, which **prevents their polymerization** into microtubules. This inhibition of microtubule formation leads to "mitotic arrest" in the metaphase, eventually causing cell death. **2. Why the Other Options are Incorrect:** * **Paclitaxel:** While it also acts on microtubules, its mechanism is the opposite. It **promotes polymerization** and stabilizes microtubules, preventing their *disassembly* (de-polymerization). This creates "frozen" microtubules. * **Etoposide:** This is a **Topoisomerase II inhibitor**. It acts in the S and G2 phases by causing DNA strand breaks. * **Irinotecan:** This is a **Topoisomerase I inhibitor**, primarily used in colorectal cancer. It prevents the religation of single-strand DNA breaks. **3. High-Yield Clinical Pearls for NEET-PG:** * **Vincristine Side Effects:** Characterized by **Peripheral Neuropathy** (paresthesia, loss of reflexes) and paralytic ileus. Notably, it is **bone marrow sparing** (minimal myelosuppression). * **Vinblastine Side Effect:** Unlike Vincristine, its dose-limiting toxicity is **Bone Marrow Suppression** (*"Blast" blasts the bone marrow*). * **Taxanes (Paclitaxel):** Common side effects include peripheral neuropathy and hypersensitivity reactions (pre-medicate with steroids/antihistamines). * **Mnemonic:** **V**incristine **P**revents polymerization; **T**axanes **T**ighten (stabilize) the polymer.

Question 230: Which of the following drugs is used in the adjuvant setting for carcinoma of the colon?

A. Bevacizumab
B. Cetuximab
C. Irinotecan
D. Oxaliplatin (Correct Answer)

Explanation: **Explanation:** **Oxaliplatin** is the correct answer because it is a cornerstone of **adjuvant chemotherapy** for Stage III (and high-risk Stage II) colon cancer. The standard adjuvant regimens are **FOLFOX** (5-Fluorouracil, Leucovorin, and Oxaliplatin) or **CAPOX** (Capecitabine and Oxaliplatin). Adjuvant therapy aims to eliminate micrometastases after surgical resection to reduce the risk of recurrence. **Analysis of Incorrect Options:** * **Bevacizumab (Option A):** This is a VEGF inhibitor (angiogenesis inhibitor). While highly effective in the **metastatic** (palliative) setting, clinical trials (like NSABP C-08) showed it provides no survival benefit in the adjuvant setting for colon cancer. * **Cetuximab (Option B):** An EGFR inhibitor used specifically for **metastatic** colorectal cancer in patients with **KRAS wild-type** tumors. Similar to Bevacizumab, it has failed to show benefit in adjuvant trials. * **Irinotecan (Option C):** A Topoisomerase I inhibitor. It is a key component of the **FOLFIRI** regimen used for **metastatic** disease. However, adding Irinotecan to adjuvant 5-FU (IFL regimen) did not improve outcomes compared to 5-FU alone and increased toxicity. **High-Yield Clinical Pearls for NEET-PG:** * **Dose-limiting toxicity of Oxaliplatin:** Peripheral sensory neuropathy (often triggered or exacerbated by **cold exposure**). * **Mechanism:** Platinum compound that forms intra-strand DNA cross-links. * **5-Fluorouracil (5-FU):** Always the "backbone" of colon cancer therapy; its action is enhanced by **Leucovorin** (folinic acid), which stabilizes the binding of 5-dUMP to thymidylate synthase. * **Microsatellite Instability (MSI-H):** Patients with Stage II colon cancer and MSI-H have a good prognosis and generally do *not* benefit from adjuvant 5-FU monotherapy.

Practice by Chapter

Principles of Cancer Chemotherapy

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Alkylating Agents

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Antimetabolites

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Antitumor Antibiotics

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Plant Alkaloids

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Topoisomerase Inhibitors

Practice Questions

Hormonal Agents

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Targeted Therapy

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Immunotherapy

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Management of Chemotherapy Side Effects

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