A 55-year-old man with newly diagnosed gastrointestinal stromal tumor (GIST) harboring a KIT mutation is referred for systemic therapy. What is the drug of choice for first-line treatment?

Question

Accepted Answer

D. Imatinib mesylate. ## KIT-Targeted Therapy in GIST

**Key Point:** Imatinib mesylate is the first-line tyrosine kinase inhibitor for KIT-mutant gastrointestinal stromal tumors (GISTs), both localized and metastatic.

### KIT Oncogene in GIST Pathogenesis
- KIT (CD117) is a receptor tyrosine kinase mutated in ~95% of GISTs
- Mutations (exon 11 > exon 9) cause constitutive kinase activation
- Drives uncontrolled proliferation of interstitial cells of Cajal
- KIT positivity is diagnostic (IHC CD117+)

### Imatinib Mechanism in GIST
1. Selectively inhibits KIT tyrosine kinase
2. Blocks downstream signaling (PI3K/Akt, MAPK)
3. Induces apoptosis in GIST cells
4. Standard dose: 400 mg daily for localized/metastatic disease

**High-Yield:** Imatinib is the only drug proven to improve overall survival in GIST and is indicated for:
- Neoadjuvant therapy (downstaging)
- Adjuvant therapy (high-risk localized GIST)
- Metastatic/unresectable GIST

### Clinical Evidence

| Setting | Benefit of Imatinib |
|---------|--------------------|
| Metastatic GIST | Median OS ~55 months vs. 20 months (historical controls) |
| Adjuvant (high-risk) | 3-year recurrence-free survival improvement |
| Neoadjuvant | Downsizing, improved resectability |

**Clinical Pearl:** Resistance to imatinib develops in ~10–15% of patients, often due to secondary KIT mutations (exon 13, 14, 17). Sunitinib is the second-line option for imatinib-resistant GIST.

### Comparison with Alternatives

| Agent | Role | Limitation |
|-------|------|------------|
| Imatinib | First-line TKI for KIT+ GIST | Resistance in minority; requires monitoring |
| Sunitinib | Second-line (imatinib resistance) | Not first-line; broader spectrum TKI |
| Doxorubicin | Chemotherapy (pre-TKI era) | Ineffective; poor outcomes in GIST |
| 5-FU | Chemotherapy for GI cancers | Not indicated for GIST; lacks KIT targeting |

**Mnemonic:** **KIT-I** = KIT mutations require Imatinib in GIST.

Answer

A. Sunitinib

Answer

B. Doxorubicin

Answer

C. 5-Fluorouracil

A 55-year-old man with newly diagnosed gastrointestinal stromal tumor (GIST) harboring a KIT mutation is referred for systemic therapy. What is the drug of choice for first-line treatment?

Explanation

KIT-Targeted Therapy in GIST

KIT Oncogene in GIST Pathogenesis

Imatinib Mechanism in GIST

Clinical Evidence

Comparison with Alternatives

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A 55-year-old man with newly diagnosed gastrointestinal stromal tumor (GIST) harboring a KIT mutation is referred for systemic therapy. What is the drug of choice for first-line treatment?

Explanation

KIT-Targeted Therapy in GIST

KIT Oncogene in GIST Pathogenesis

Imatinib Mechanism in GIST

Clinical Evidence

Comparison with Alternatives

Practice similar questions

Join our NEET PG community

Setting	Benefit of Imatinib
Metastatic GIST	Median OS ~55 months vs. 20 months (historical controls)
Adjuvant (high-risk)	3-year recurrence-free survival improvement
Neoadjuvant	Downsizing, improved resectability

Agent	Role	Limitation
Imatinib	First-line TKI for KIT+ GIST	Resistance in minority; requires monitoring
Sunitinib	Second-line (imatinib resistance)	Not first-line; broader spectrum TKI
Doxorubicin	Chemotherapy (pre-TKI era)	Ineffective; poor outcomes in GIST
5-FU	Chemotherapy for GI cancers	Not indicated for GIST; lacks KIT targeting