Does a squamous cell carcinoma in situ on the frontal scalp require Mohs surgery?

Squamous Cell Carcinoma In Situ on the Frontal Scalp: Mohs Surgery is NOT Necessary

For squamous cell carcinoma in situ (SCCIS) on the frontal scalp, Mohs surgery is not required and multiple alternative treatments are more appropriate, including photodynamic therapy, curettage with cautery, topical 5-fluorouracil, or standard excision with 4-6 mm margins. 1

Why Mohs is Overutilization for SCCIS

• SCCIS is a superficial, indolent, low-risk tumor that rarely progresses to invasive disease after definitive treatment, making the tissue-sparing precision of Mohs surgery unnecessary 2
• The evidence base for Mohs in SCCIS is weak, carrying only a Level D recommendation (expert opinion only) from the British Association of Dermatologists 1
• Most primary SCCIS in non-immunosuppressed patients should be scored as inappropriate or uncertain for Mohs surgery, as multiple other efficacious treatments exist 2
• The scalp location alone does not justify Mohs for in situ disease, as the high-risk location criteria apply primarily to invasive squamous cell carcinoma 3

Preferred Treatment Options for Scalp SCCIS

First-Line: Photodynamic Therapy (PDT)

• PDT has the highest level of evidence (Level A recommendation) with complete clearance rates of 88-100% at 3 months 1
• PDT offers superior cosmesis compared to cryotherapy and 5-fluorouracil, particularly advantageous for cosmetically sensitive areas like the frontal scalp 1

Second-Line: Curettage with Cautery

• Simple, inexpensive, safe, and effective (Level C recommendation), preferable to cryotherapy in terms of pain, healing, and recurrence rate 1
• Appropriate for small (<1 cm), well-differentiated, primary, slow-growing lesions on sun-exposed sites 1
• Requires repeating the curettage-cautery cycle 1-2 times for adequate treatment 1

Third-Line: Topical 5-Fluorouracil 5%

• Practical for large lesions (Level B recommendation), especially useful when multiple lesions are present 1

Fourth-Line: Standard Excision

• Standard excision with 4-6 mm margins is adequate for well-defined lesions <2 cm 1
• Surgical excision has the lowest recurrence rate at 0.8% in retrospective studies 4

Critical Caveats

When Curettage is Contraindicated

• Do NOT use curettage on terminal hair-bearing skin (scalp, beard, pubic, axillary regions) due to potential follicular extension of tumor 3
• This is a major pitfall: the frontal scalp is hair-bearing, which technically excludes curettage as an option unless the area is completely bald 3
• Curettage has no histologic margin control, making it impossible to confirm complete tumor removal 1

When to Consider Mohs

The British Association of Dermatologists recommends Mohs for SCCIS only in these specific scenarios:

• Digital SCCIS (fingers/toes) where tissue conservation is critical 1
• Some cases of genital SCCIS 1
• Recurrent disease after failed initial treatment 5
• Poorly defined clinical margins where tumor extent is unclear 5

Practical Algorithm for Frontal Scalp SCCIS

1. If the lesion is small (<2 cm), well-defined, and the patient is not immunosuppressed: Consider PDT as first choice for best cosmetic outcome 1

2. If the area is completely bald (no hair follicles): Curettage with cautery is acceptable 3, 1

3. If the area has hair follicles present: Avoid curettage; use PDT, topical 5-FU, or excision 3

4. If the lesion is large or multiple: Topical 5-fluorouracil 5% cream 1

5. If definitive histologic confirmation of clearance is desired: Standard excision with 4-6 mm margins and postoperative margin assessment 1

6. Reserve Mohs only for: Recurrent disease after failed treatment or if margins are truly impossible to define clinically 1, 5