Procedures: Skin Cancer Treatment

Skin cancer treatment with Mohs surgery

What is Mohs surgery?

Mohs surgery or Mohs micrographic surgery is the gold-standard and most precise technique available for removal of most skin cancers and has the highest cure rate (98-99%). It treats skin cancers on the face where it is critical to remove the minimum amount of tissue for cosmetic and functional reasons and to ensure no tumor is left behind.

Mohs Treatment Seattle


Mostly, it is a technique that allows the doctor to test the edges of the excision on the day of the surgery, while you wait. It will enable the doctor to remove the narrowest possible margin of healthy skin around the tumor, keeping the surgery site as small as possible.

Mohs micrographic surgery was named after its inventor, Dr. Frederick Mohs, an American dermatologist, and surgeon. A Mohs surgeon requires many years of medical and specialized training and, as such there is currently a shortage of MOHS surgeons in the Pacific Northwest, making Dr. Jenkin of Seattle Dermatology Associates of Seattle one of the top, leading, and the premier choice for personalized, full-service dermatology care.


What is the difference between Mohs surgery and standard excision?

Skin Cancer Treatment

In standard excision, the tissue sample is sent off for histological processing while the incision is closed. The processing takes many days during which cross sections (or vertical sections) are created at various distances through the sample and are microscopically assessed by a pathologist. The pathologist looks for skin cancer at the margins of each section, but these are only a fraction of the actual excision margin.

In Mohs surgery, the histological processing takes place on the day of surgery, and the incision is only closed after it has been confirmed that entire cancer has been successfully removed. The excision margin is examined by an embedding technique that allows horizontal sections to be cut involving all the low and radial excision margins. If any tumor is visible in these parts, it means that the excision is incomplete and the patient requires a further Mohs stage.

A mapping process and color coding system is used during Mohs surgery to precisely localize any remaining cancer, and tissue is only removed if it contains cancer. This method preserves healthy tissue.

Mohs surgery yields higher clearance rates than standard excision, and smaller incisions — therefore better cosmetic results.


The Steps Involved in Mohs surgery - Mohs surgery is a single day procedure under local anesthesia which includes the following steps:

Step 1: The visible tumor plus a small margin is outlined using a skin marker, and a reference map or grid is drawn on the patient (often using temporary sutures).
Step 2: The area is excised at the radial margins.
Step 3: Haemostasis is obtained, and the incision is temporarily dressed.
Step 4: The excised tissue sample is divided into two or more sections that are color-coded using special tissue dyes.
Step 5: A mapping process ensures that a residual tumor seen under the microscope can later be matched to the exact location of the patient using a paper-based map or digital photographs and image processing software.
Step 6: Our specialized biomedical scientists embed and freeze the tissue in a cryostat to create horizontal sections of the entire excision margin.
Step 7: The Mohs surgeon examines the microscopic sections for remaining cancer.

Any remaining cancer is drawn on the map or digital image:

The process is repeated until the patient is tumor free.
The incision is closed, see incision closure topic for an overview of techniques.


Types of skin cancer which are best treated with Mohs surgery:

Mohs surgery is the first choice of treatment for high-risk basal cell carcinoma and squamous cell carcinoma. One reason to perform Mohs is to minimize the risk of incomplete excision. Mohs reduces financial burdens to the patient helping avoid extensive and costly re-excisions later.


Mohs surgery has the most significant benefit for a tumor at
high risk of incomplete excisions, including:

Recurring: Recurrent or incompletely excised tumor
Regrowth: Tumor arising in skin previously exposed to radiotherapy.
Large Tumors: Large tumor, especially in the head and neck area.
Irregular Tumors: Tumors that have oddly defined borders
Basel Cell Growth: Basal cell carcinoma with an aggressive growth pattern on histology (infiltrative, micronodular or with perineural invasion)
Squamous Cells: Squamous cell carcinoma at higher risk of metastasis.

Important to know:

Mohs may also be appropriate when a significant reconstruction is needed to close the incision or with tumor removal procedures located in cosmetically sensitive areas.

In 2012, a joint effort by various medical organizations in the USA led to the development of appropriate use criteria for Mohs surgery. These requirements may be used as guidance when considering Mohs surgery although they may not apply in all jurisdictions.


Mohs for other skin cancer types:

Plenty of evidence supports that Mohs is the best form of surgery for high-risk basal cell carcinoma and squamous cell carcinoma. Large clinical trials comparing Mohs to standard excision for remaining types of skin cancer are lacking.


Dermatology Associates of Seattle accurately identifies tumors.

In Mohs surgery, tumor cells require accurate identification by microscopic examination of frozen sections which can be challenging in some skin cancers, including:

Atypical Fibroxanthoma: (AFX) is a tumor that occurs primarily in older individuals after the skin of the head and neck has been damaged significantly by sun exposure and/or therapeutic radiation.
Dermatofibrosarcoma Protuberans: (DFSP) is a rare tumor. It is a rare neoplasm of the dermis layer of the skin, and is classified as a sarcoma. There is only about one case per million per year. DFSP is a fibrosarcoma, more precisely a cutaneous soft tissue sarcoma.
Microcystic Adnexal Carcinoma: (MAC) is a rare, malignant appendage tumor commonly classified as a low-grade sweat gland carcinoma that typically occurs on the head and neck, particularly the central face. Microcystic adnexal carcinoma shows aggressive local invasion but has little metastatic potential.
Melanoma in Situ: (in situ) In Stage 0 melanoma, the malignant tumor is still confined to the upper layers of the skin (epidermis). This means that the cancer cells are only in the outer layer of the skin and have not grown any deeper. The term for this is in situ, which means “in place” in Latin.
Extramammary Paget Disease: (EMPD), also extramammary Paget disease, is a rare, slow-growing, usually noninvasive intraepithelial (in the skin) adenocarcinoma outside the mammary gland and includes Paget's disease of the vulva and the extremely rare Paget's disease of the penis.
Skin Cancer Removal

Said tumors require variations of Mohs surgery to be implemented following the standardized principles of Mohs surgery (use of microscopic margin control, horizontal embedding, and mapping and color coding of tissue) but use paraffin-embedded sections versus frozen sections.


This procedure allows the use of immunohistochemical markers to help identify tumor cells. Plenty of evidence supports that Mohs is the best form of surgery for high-risk basal cell carcinoma and squamous cell carcinoma. Large clinical trials comparing Mohs to standard excision for remaining types of skin cancer are lacking.

Is Mohs surgery cost-effective?

Mohs surgery leads to fewer tumor recurrences compared to standard excision of basal cell carcinoma and squamous cell carcinoma. Average recurrence rates for Mohs surgery statistics reports show 1–5%, depending on the type of tumor and length of follow-up.


Clinical trials with 8-10 year check-ups, recurrence rates show:

Carcinoma Removal: 4.4% for Mohs, 12.2% for standard excision of high risk primary basal cell carcinoma removal.
Basal Cell Carcinoma: 3.9% for Mohs surgery and 13.5% for conventional excision for high risk recurrent basal cell carcinoma
Long-term Cost Savings: Studies show that Mohs is a much more cost-effective treatment than standard procedures.
Success Ratio: The main reason for Mohs long-term savings in cost is due to it requiring fewer costly operations for recurrent tumors compared to standard excision.

Seattle Skin Cancer Experts

The first step is consultation:

Given that every situation and personal status is different, it's difficult knowing which is the best first step to take. Understanding how every skin condition differs, we recommend any patients seeking Mohs surgery to set up a consultation with Dr. Jenkin by calling us direct at:
(206) 267-2100.


Online Consultation Request