Mohs Micrographic Surgery for Superficially Invasive Squamous Cell Carcinoma
Mohs micrographic surgery (MMS) is the preferred treatment for superficially invasive squamous cell carcinoma, particularly for high-risk tumors and those in anatomically sensitive locations, due to its superior cure rates and tissue conservation. 1
Rationale for Mohs Surgery in Superficially Invasive SCC
- MMS provides complete assessment of all peripheral and deep margins, which is critical for ensuring complete tumor removal and minimizing recurrence risk 1
- MMS is documented to have superior efficacy compared to other treatment modalities, with 5-year recurrence rates of only 3.1% for primary SCC compared to 8.1% for standard excision 1
- Superficially invasive SCC often has subclinical extension beyond visible margins, making complete margin assessment essential 2
- MMS achieves maximum tissue conservation while ensuring complete tumor removal, which is particularly important for cosmetically and functionally sensitive areas 3
Indications for Mohs in Superficially Invasive SCC
MMS is particularly indicated for superficially invasive SCC in the following scenarios:
- High-risk anatomic locations (H-zone of the face, periorbital, perioral, ears) 1
- Tumors with poorly defined clinical margins 1
- Recurrent tumors (MMS shows 10% recurrence rate vs. 23.3% with standard excision) 1
- Tumors requiring tissue conservation for functional or cosmetic outcomes 3
- Tumors with aggressive histologic features or perineural involvement 4
Evidence Supporting Mohs for Superficially Invasive SCC
- A systematic review of literature from 1974 to 2023 demonstrated that MMS consistently exhibits significantly lower risk of recurrence compared to conventional excision for SCC 3
- MMS has demonstrated excellent outcomes for high-risk SCC with only 1.2% local recurrence rate and 2.3% metastasis rate in a large single-center study 4
- For SCC of the lip, MMS has shown 92% disease-free rate at 5 years, with no tumor-related deaths or metastases 5
- Even for superficially invasive SCC, MMS often requires multiple stages for complete clearance, highlighting the importance of comprehensive margin control 2
Alternative Treatment Options
When MMS is unavailable or inappropriate, alternative options include:
- Standard excision with complete circumferential peripheral and deep margin assessment (CCPDMA) using intraoperative frozen section assessment 1
- For low-risk, small (<1 cm), well-differentiated tumors on sun-exposed sites, curettage and electrodesiccation may be considered 1
- Radiation therapy can be considered for non-surgical candidates, typically reserved for patients older than 60 years due to long-term sequelae concerns 1
Important Considerations and Caveats
- The tumor debulk specimen from MMS should be submitted for paraffin sections to document high-risk features when needed 1
- Incomplete surgical excision is associated with worse prognosis; when using standard excision, consider delaying wound repair until negative margins are confirmed 1
- Patients with one high-risk SCC are likely to develop secondary primary SCCs and should be monitored closely 4
- For SCC with perineural invasion involving named nerve trunks, adjuvant radiation therapy may be considered in addition to MMS 4
- Treatment of coexisting actinic cheilitis (for lip SCC) may lower the risk for local recurrence after MMS 5
In conclusion, while multiple treatment options exist for superficially invasive SCC, MMS offers the highest cure rates with maximal tissue conservation, making it the preferred treatment modality, especially for high-risk tumors or those in cosmetically and functionally sensitive areas.