What is the recommended treatment for skin cancer using Mohs (Micrographically controlled excision) surgery?

Mohs Micrographic Surgery for Skin Cancer Treatment

Mohs micrographic surgery is the recommended first-line treatment for high-risk skin cancers, providing the highest cure rates while preserving normal tissue through complete circumferential peripheral and deep margin assessment. 1

Indications for Mohs Surgery

Mohs surgery is specifically indicated for:

• High-risk basal cell carcinomas (BCCs) 2
• High-risk squamous cell carcinomas (SCCs) 2, 1
• Recurrent skin cancers 2
• Tumors in cosmetically and functionally sensitive areas (face, hands, genitalia) 3
• Tumors with poorly defined clinical borders 4
• Tumors with aggressive histologic subtypes 2, 4
• Large tumors (>2 cm) 2
• Tumors with perineural invasion 2

Advantages of Mohs Surgery

• Superior cure rates: 5-year recurrence rates of only 1% for primary BCC and 5.6% for recurrent BCC 2
• Complete margin control: Examines 100% of surgical margins, unlike standard excision's "bread-loaf" sampling 4, 5
• Tissue preservation: Removes only tissue containing tumor, maximizing cosmetic and functional outcomes 3, 5
• Same-day results: Allows for immediate reconstruction after tumor clearance 5

Comparative Effectiveness

When comparing treatment modalities for skin cancer:

• Primary BCC: Mohs has 1% recurrence rate vs. 8.1% for standard excision 2
• Primary SCC: Mohs has 3.1% recurrence rate vs. 8.1% for standard excision and 10.0% for radiation therapy 2
• High-risk SCC: Mohs shows significantly lower recurrence rates compared to standard excision:
  • 25.2% vs. 41.7% for tumors ≥2 cm
  • 32.6% vs. 53.6% for poorly-differentiated SCC
  • 0% vs. 47% for neurotropic SCC 2
• Recurrent SCC: Mohs has 10.0% recurrence rate vs. 23.3% for standard excision 2

Treatment Algorithm for Skin Cancer

1. Risk stratification:

   • Low-risk BCC: Small (<2 cm), well-defined, primary tumors in non-critical areas
   • High-risk BCC/SCC: Large (>2 cm), poorly defined borders, aggressive histology, recurrent tumors, or critical anatomic locations

2. Treatment selection:

   • High-risk tumors: Mohs micrographic surgery or resection with complete margin assessment 2
   • Low-risk tumors: Options include:
     • Standard excision with 4-6 mm margins 2
     • Curettage and electrodesiccation (for superficial, well-defined tumors) 2
     • Radiation therapy (for non-surgical candidates) 2, 6

3. Management of positive margins:

   • If positive margins after Mohs: Additional Mohs layers until clear margins
   • If positive margins after standard excision: Re-excision or Mohs surgery 2
   • If further surgery contraindicated: Consider radiation therapy or systemic therapy 2

Important Considerations and Pitfalls

• Avoid curettage and electrodesiccation for high-risk tumors or those extending to specimen base 1
• Delayed reconstruction is advisable when doubt exists about margin clearance 1
• Aggressive histologic patterns (spindle cell, single cell infiltrative) may be poorly visualized with frozen sections, potentially limiting Mohs effectiveness in certain cases 2
• Standard excision with 4-6 mm margins is insufficient when deep margin involvement is present 1
• Positive surgical margins after standard excision significantly increase recurrence risk (26.8% vs. 5.9% with negative margins) 2

Mohs surgery remains the gold standard for treatment of high-risk skin cancers, particularly on the face and other cosmetically sensitive areas, offering superior cure rates while maximizing tissue preservation 6, 7.