A 58-year-old Indian man with metastatic renal cell carcinoma (clear-cell type) is initiated on sunitinib, a multi-targeted tyrosine kinase inhibitor. After 2 weeks of therapy, he develops severe hypertension (BP 165/105 mmHg), and after 6 weeks, he complains of hand-foot skin reaction with painful erythema and blistering on his palms and soles. Which of the following best explains the mechanism underlying the hand-foot skin reaction?

Explanation

## Hand-Foot Skin Reaction (HFSR) with Multi-Targeted TKIs **Key Point:** Hand-foot skin reaction is a class effect of multi-targeted tyrosine kinase inhibitors (sunitinib, sorafenib, regorafenib) and results from inhibition of VEGFR and PDGFR in the microvasculature of acral skin. ### Pathophysiology of HFSR 1. **VEGFR/PDGFR inhibition in dermal vasculature:** - Sunitinib blocks VEGFR-1, VEGFR-2, VEGFR-3, and PDGFR-α/β - These receptors are critical for endothelial cell survival and vascular integrity 2. **Endothelial dysfunction:** - Loss of VEGF-mediated survival signals → endothelial cell apoptosis - Increased vascular permeability - Microthrombi formation in dermal capillaries 3. **Acral predilection:** - Palms and soles have high metabolic demand and pressure - Increased shear stress on already-compromised capillaries - Sweat gland ducts concentrate the drug 4. **Clinical result:** - Erythema, edema, blistering, desquamation - Typically occurs 2–6 weeks after initiation - Painful and can be dose-limiting **High-Yield:** HFSR is **NOT** an allergic or immune-mediated reaction—it is a direct vascular toxicity from TKI activity. This is why it responds to dose reduction or interruption, not immunosuppression. ### Clinical Management - Dose reduction or treatment interruption - Supportive care: emollients, keratolytic agents (urea, salicylic acid) - Avoid pressure on affected areas (soft footwear) - Topical corticosteroids for inflammation - Rarely, complete cessation if severe ### Hypertension with Sunitinib Sunitinib also causes hypertension through: - VEGFR inhibition → loss of endothelial NO production - Increased systemic vascular resistance - Fluid retention **Clinical Pearl:** Baseline and regular BP monitoring is essential. Antihypertensive agents (ACE inhibitor or calcium channel blocker) are often needed concurrently. | Feature | HFSR with TKI | Allergic Dermatitis | Immune Complex Disease | |---------|---------------|-------------------|------------------------| | Onset | 2–6 weeks | Hours to days | Variable, often systemic | | Distribution | Acral (palms/soles) | Generalized or contact-based | Often symmetric, may include face | | Histology | Vascular injury, endothelial apoptosis | Lymphocytic infiltrate | IgG/C3 deposition at DEJ | | Response to dose reduction | Yes | No | No | | Rechallenge risk | Lower with dose adjustment | High recurrence | High recurrence | [cite:KD Tripathi 8e Ch 51; Harrison 21e Ch 397]