Mohs Surgery for Basal Cell vs. Squamous Cell Carcinoma: What’s the Difference?

Skin cancer is the most common form of cancer in the United States, with millions of cases diagnosed annually. Among the various types, basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) are the two most prevalent forms of non-melanoma skin cancers. One of the most effective treatments for these types of cancer is Mohs micrographic surgery — a specialized surgical technique that allows for the precise removal of cancerous tissue while preserving as much healthy tissue as possible.

Mohs surgery is widely regarded as the gold standard for treating BCC and SCC, particularly in areas where cosmetic and functional outcomes are critical. However, the approach to using Mohs can vary depending on the tumor type. In this blog post, we will explore how Mohs surgery is used for BCC and SCC by examining the nature of each cancer, the surgical nuances involved, and what patients can expect before, during, and after treatment.

What is Mohs Surgery?

Mohs surgery, named after Dr. Frederic Mohs who developed the technique in the 1930s, involves the sequential removal and microscopic examination of thin layers of skin. After each layer is removed, it is immediately examined under a microscope to determine if any cancer cells remain. If so, another layer is removed from the precise area where the cancer persists. This process continues until no cancer cells are detected.

Key benefits of Mohs surgery include:

• High cure rate: Per the American Academy of Dermatology, Mohs surgery offers a cure rate of up to 99% for primary BCCs and 97% for recurrent BCCs. For SCCs, the cure rate ranges between 94% to 97% for primary tumors.
• Tissue preservation: By removing only cancerous tissue and sparing healthy tissue, Mohs provides the best cosmetic and functional outcomes — especially important for areas like the nose, ears, lips, and eyelids.
• Real-time pathology: Immediate microscopic evaluation reduces the likelihood of cancer recurrence and eliminates the need for multiple procedures.
• Outpatient procedure: It is performed under local anesthesia, minimizing recovery time and risks associated with general anesthesia.

Understanding Basal Cell Carcinoma (BCC)

According to a study by the National Institutes of Health (NIH), basal cell carcinoma is the most common type of skin cancer, accounting for approximately 80% of all non-melanoma skin cancers. It originates in the basal cells of the epidermis, which are responsible for producing new skin cells.

Characteristics of BCC:

• Slow-growing: BCC grows gradually and rarely metastasizes to distant parts of the body.
• Locally invasive: If left untreated for a prolonged period, it can cause significant local damage to skin, bone, and surrounding tissues.
• Appearance: Often appears as a pearly or waxy bump, sometimes with visible blood vessels or ulceration. Other forms may be flat and scaly.
• Common locations: Face, ears, neck, scalp, shoulders, and back—areas frequently exposed to the sun that may have had sunburns in the past.

When Mohs surgery is recommended for BCC:

• When the tumor is recurrent.
• Located in a cosmetically or functionally sensitive area (e.g., around the eyes, nose, lips, or ears).
• When the tumor is large, has ill-defined borders, or displays aggressive histologic subtypes (e.g., morpheaform, infiltrative).

Understanding Squamous Cell Carcinoma (SCC)

According to the Skin Cancer Foundation, squamous cell carcinoma is the second most common skin cancer, making up about 20% of non-melanoma skin cancers. SCC arises from the squamous cells that make up the outer layer of the skin (the epidermis).

Characteristics of SCC:

• Faster-growing: SCC tends to grow more quickly than BCC.
• Higher metastatic risk: Unlike BCC, SCC has a greater potential to spread to lymph nodes or internal organs, especially when found on the lips, ears, or in immunocompromised individuals.
• Appearance: Often appears as a scaly red patch, open sore, thickened skin, or wart-like growth that may crust or bleed.
• Common locations: Face, ears, neck, scalp, hands, arms, and legs — areas of chronic sun exposure.

When Mohs surgery is recommended for SCC:

• High-risk location or large tumors.
• Aggressive histological features (e.g., poorly differentiated cells, perineural invasion).
• Recurrent tumors or those in immunosuppressed patients (e.g., organ transplant recipients or those taking immunosuppressive medications).
• Tumors with unclear borders or history of incomplete excision.

How Mohs Surgery Differs for BCC vs. SCC

While the Mohs surgical technique remains the same for both cancers, the approach may differ based on the behavior of the tumor.

Tumor behavior:

• BCC grows slowly and locally, allowing for a conservative approach.
• SCC can invade deeper and has a greater risk of metastasis, sometimes requiring deeper surgical margins.

Tissue removal approach:

• BCC: Surgeons often start with narrower margins, especially if the tumor is small or well-defined. Tumors with aggressive histologic features (such as infiltrative) may require wider margins to clear.
• SCC: May necessitate wider initial margins, particularly if the tumor is high-risk or poorly defined.

Microscopic evaluation:

• Both tumors can be identified via microscopic examination. If any tumor cells are seen at the surgical margin, another layer of tissue is removed.

Recurrence risk management:

• BCC: Lower recurrence risk post-Mohs, especially for primary tumors.
• SCC: Success rate of Mohs is high with low-risk SCC. It may require closer follow-up additional imaging or adjuvant therapy if aggressive features are present (though usually this is not required).

Adjunct considerations:

• Skin cancer in immunocompromised patients (e.g., transplant recipients) sometimes warrants multidisciplinary care. These patients are typically seen for frequent follow up for surveillance of new skin cancers or recurrence.

Key Differences in BCC vs. SCC

What to Expect During Mohs Surgery (For Either Type)

Patients undergoing Mohs surgery for either BCC or SCC can expect a structured and efficient experience.

1. Consultation and mapping:

• The surgeon will review your biopsy, medical history, and examine the lesion.
• The treatment area will be marked and photographed for surgical planning.

2. Step-by-step surgical process:

• Step 1: Local anesthesia is administered.
• Step 2: The visible tumor is removed along with a thin margin of surrounding tissue.
• Step 3: The tissue is mapped, color-coded, frozen and processed to make microscope slides for immediate microscopic examination.
• Step 4: If cancer cells remain, the surgeon removes another layer only in the affected area, repeating the process until margins are clear.

3. Time commitment and stages:

• Most procedures last 2 to 4 hours, though it can take longer if multiple stages are required.
• On average, 1 to 3 stages are needed to achieve complete tumor clearance.

4. Reconstructive options:

• After clearance, the wound is repaired via sutures via primary closure, skin graft, or a skin flap, depending on size and location.
• In some cases, reconstruction is done the same day, while in complex cases, a referral to a plastic surgeon may be made (this is typically planned in advance).

Recovery and Follow-up

Post-procedure care:

• Keep the wound clean and dry for 24 to 48 hours.
• Apply prescribed ointments and change dressings as instructed.
• Mild discomfort, swelling, or bruising is common and typically resolves within a week.
• Learn more about Mohs surgery recovery

Scar care and long-term outcomes:

• As with any surgery, scarring is possible but often minimal due to tissue-sparing technique.
• Over-the-counter silicone gel or prescribed treatments can improve cosmetic appearance.
• In most cases, aesthetic outcomes are superior to traditional excision.

Importance of ongoing surveillance:

• Patients with a history of skin cancer are at increased risk for future lesions.
• Performing monthly self-skin checks as well as routine full-body professional skin exams (every 6 to 12 months) are critical, especially for SCC patients, who may require more frequent monitoring.
• Sun protection and regular self-exams are also essential.

Mohs surgery remains a cornerstone treatment for both basal cell and squamous cell carcinomas, with tailored strategies based on the type, location, and behavior of the tumor. While BCC typically prioritizes tissue conservation due to its low metastatic risk, SCC sometimes demands a more aggressive approach given its potential for spread and recurrence.

Early detection and timely treatment are crucial to achieving the best outcomes. Patients should always consult with a board-certified Mohs surgeon, especially when dealing with high-risk or cosmetically sensitive skin cancers.

Whether you are facing BCC or SCC, understanding your treatment options — and the differences between them — can help you make informed decisions for your skin health and overall well-being.

Jessica “Nikki” Dietert, MD is a board-certified dermatologist ad fellowship-trained Mohs surgeon at Westlake Dermatology. She then earned her medical degree at The University of Texas Southwestern Medical School in Dallas before completing a residency at The University of Texas at Houston/M.D. Anderson Cancer Center, where she served as chief resident in her final year. She then finished training with a fellowship in Mohs micrographic surgery at Washington University in St. Louis.

Disclaimer: The contents of the Westlake Dermatology website, including text, graphics, and images, are for informational purposes only and are not intended to substitute for direct medical advice from your physician or other qualified professional.