Mohs Surgery

Read below to find out more about Mohs surgery.

Mohs Surgery


Mohs micrographic surgery is a specialized surgical procedure used to treat skin cancers, typically of the head and neck. Recurrent or more advanced tumors of the rest of the body are sometimes treated with Mohs surgery as well. The technique offers two main advantages over traditional skin cancer removal treatments:

  • The best cure rate. Mohs surgery for primary basal cell carcinoma, for example, has a 98% cure rate.
  • Tissue sparing. Because Mohs surgery is a tissue sparing surgery, where only the skin with tumor in it is removed, the patient is left with the smallest defect possible. Smaller defects mean smaller scars in the end, after the defect is closed. In traditional excisions, the edges are not checked in "real-time" so safety margins are necessary. This often leads to larger defects and eventually larger scars. On the face, even a couple of millimeters difference in a scar length can make a big cosmetic difference. (See below for more about scars.)

Mohs surgery involves a same-day procedure where an initial "layer" is taken (the clinical tumor) and examined under the microscope for any involvement of the edges while the patient waits. The tissue is mapped in such a way so that if there is tumor at any one edge, the surgeon knows exactly which edge this is and can go back to take another small piece of skin from this edge only (instead of another whole circle around the defect, leaving a larger defect than necessary).


The two most common skin cancers treated with Mohs surgery are basal cell carcinoma and squamous cell carcinoma. The cure rates with Mohs surgery are up to 99% for primary cancers and 95% for recurrent cancers. Other types of skin cancers such as sebaceous carcinoma, atypical fibroxanthoma, dermatofibrosarcoma protuberans and others can also be treated with Mohs surgery.


Dr. Ken K. Lee will perform your Mohs surgery. He has extensive experience and knowledge of this procedure.

Dr. Ken K. Lee specializes in all aspects of dermatologic surgery with a special emphasis on Mohs Micrographic Surgery (a precise technique to remove skin cancers), reconstructive surgery, laser and cosmetic surgery.  He joined Portland Dermatology Clinic in 2010 after serving 12 years on the faculty at Oregon Health and Science University.  During his tenure, he was the Director of Dermatologic Surgery and Associate Professor in the Departments of Dermatology, Surgery, and Otolaryngology/Head & Neck Surgery. 

Dr. Lee received his undergraduate degree from Johns Hopkins University and medical degree from Cornell University.  He completed an internal medicine residency at Stanford University followed by dermatology residency and advanced dermatologic and Mohs Surgery fellowship at Oregon Health and Science University.

Dr. Lee is widely recognized for his expertise on skin cancer, cosmetic, and dermatologic surgery, having presented over 100 lectures at national and international conferences.   A renowned researcher, Dr. Lee was the principle investigator of a cancer research project awarded by the National Cancer Institute/National Institute of Health. Dr. Lee was also was a member of both research projects that led to the FDA approval of BOTOX® and Dysport®.

Dr. Lee has held leadership positions in many organizations including serving on the Boards of Directors for the prestigious organizations American Society for Dermatologic Surgery, American College of Mohs Surgery, and the Association of Academic Dermatologic Surgeons.  He is the principle author of the textbook Color Atlas of Cutaneous Excisions and Repairs and has written numerous research articles and book chapters.  He frequently appears in regional and national media and has been featured as the laser expert in ELLE Magazine.


Mohs surgery is a highly sophisticated procedure performed by a team of medical personnel that includes the surgeon, nurses, and technicians. It is an outpatient procedure performed under local anesthesia. 

On the day of the surgery, the area of the biopsied skin cancer is identified together by you and Dr. Lee. After the region is adequately numbed, the visible cancer is scraped using a curette to better delineate the cancer. A narrow margin is then taken around and underneath with a scalpel so that a disc shaped piece of skin is removed. The blood vessels are sealed using an electrocautery and a pressure dressing is applied. The removed tissue is mapped, oriented and marked with colored ink and submitted to the technicians to process. The specimen is frozen, cut, stained and placed on a glass slide. Dr. Lee then carefully examines the slides under the microscope to look for any residual cancer on the margins. Unlike other types of biopsy and pathology tests where only 1-2% of the cancer margin is visualized, Mohs processing is very unique in that virtually 100% of the cancer margin is visualized. Combining that with the added precision of the surgeon reading the pathology slides gives Mohs surgery the highest cure rate. Each removal and processing of tissue called a “stage” takes approximately 1 hour.

If cancer is visualized under the microscope, the surgeon marks the area on the map. The patient is brought back into the procedure room and additional tissue is precisely removed from the positive region and submitted to the Mohs lab. This process is repeated until the margins are clear of cancer. On the average, it takes two to three “stages” to clear the cancer.

Once the Mohs surgery is complete, you will have a wound/defect which can vary in size but will always be larger than what was seen initially with the naked eye. The second part of the procedure is the repairing this wound. Although Mohs surgery allows for maximal tissue preservation, all surgery results in a scar. Dr. Lee is an experienced reconstructive surgeon and will review the options and recommend the repair that would likely result in the best cosmetic and functional outcome.

Types of repairs:

  • Primary Closure: The skin surrounding wound is loosened then closed in straight line using layers of deep and superficial sutures. The incision line will be longer than you may expect as the final length is usually three times as long as the diameter of the wound.
  • Flap: The skin adjacent to the wound is elevated and moved to cover the defect. Flaps are typically used for larger wounds but can also be used for wounds in delicate areas, under tension, and to minimize distortion.
  • Skin graft: Skin from a different area of the body is used to cover the wound. This type of repair can take longer to heal but can provide excellent results.
  • Healing by granulation: The wound is left open and allowed to heal in on its own. Certain areas heal very well by this manner though typically will take the longest to heal.

Click to view a Mohs Surgery diagram of the process.


Watch this video to learn more about the Mohs surgery process. Click to watch a Mohs Surgery video.


Most patients are scheduled directly for Mohs surgery without a preoperative visit. A brief consultation will be done on the day of the procedure. If you would like to see Dr. Lee in consultation prior to your surgery date, we will gladly schedule an appointment upon request.

The surgery is performed under local anesthesia. We suggest that you eat a normal breakfast or lunch, unless otherwise specified. Please bathe or shower and wash your hair to minimize your risk of a surgical site infection.

It is recommended you do no travel or plan to participate in athletic activities for 7-10 days following surgery, please plan accordingly.

It is important that you do NOT take any anti-anxiety medicines, narcotic pain medicines, or similar types of medicines on the day of the surgery. Once you have consulted with Dr. Lee, we can provide you with an anti-anxiety medication. For Mohs surgery, you will be here for several hours, so bring a book, magazine, or laptop. We recommend that you have someone accompany you to give you a ride home. This is a requirement if you receive anti-anxiety medicines.

It is essential that you are able to positively identify the biopsy site on which surgery will be performed. If you cannot, please let us know ahead of time. You may need to go to your referring physician to have the site marked.

Many patients are on blood thinning medications that are prescribed by their physicians. We do not recommend stopping them without explicit permission from the prescribing physician. For those on Coumadin/Warfarin, please make sure that your INR is in the therapeutic range. if approved by your prescribing physician, please discontinue any blood thinning medications one week prior to surgery. Do not discontinue any recommended medications, including aspirin, without permission from your prescribing doctor.

Please stop taking anti-inflammatory medicines (like ibuprofen, Advil, Motrin, Naprosyn, Anacin, and Bufferin), alcohol, vitamin E, ginko biloba, fish oil, and garlic pills at least one week before your surgery. These can increase your risk of bleeding during surgery.

Please bring photo ID and your current insurance card(s) with you to your appointment. If you will be a new patient to Portland Dermatology Clinic, we strongly encourage you to complete our new patient forms through our online Patient Portal prior to your scheduled appointment. Once scheduled, our office will gladly provide you with access. If you would prefer to complete hard copies, let us know and we can mail them prior to your scheduled appointment. You can then bring them competed to your appointment.

View and print a Preparing for Surgery with Dr. Lee handout. If you have questions, please call our office at 503-445-2136.


Most people will experience remarkably little discomfort after surgery. Usually Tylenol is sufficient to control the pain. If you would like a stronger prescription pain medication, we will gladly prescribe this for you.

Bruising and swelling
Bruising and swelling are common following surgery and usually lasts for several days. Applying ice in the first 24 hours helps reduce these symptoms.

The infection rate is very low. A preoperative antibiotic may be recommended to some patients. It is typical to develop some redness along the suture line but if it becomes more extensive or if you develop increasing pain, swelling, drainage, please notify us immediately.

The risk of significant post-operative bleeding is very low. Upon completion of the surgery, a pressure bandage will be placed on the wound. Small number of patients may have some post-operative bleeding as the epinephrine (adrenaline) in the anesthetic wears off. This usually can be stopped with direct pressure for 20 minutes. For any bleeding that is not controlled with pressure, we need to be notified immediately.

At times, the area surrounding your operative site will be numb to the touch. This area of numbness may persist for several months or longer. In some instances it may be permanent. If this occurs, please discuss it with your physician at your follow-up visit.

Although every effort will be made to offer the best possible cosmetic result, you will be left with a scar. The scar will often be longer than what you may have anticipated because cancer that is underneath the surface is larger than what is visible before surgery. The scar may also need to be lengthened to better fit the contours of the skin. Scars can take a few months or longer to heal completely. The scar can be minimized by the proper care of your wound. We will discuss wound care in detail with you and give you wound care information, which will explicitly outline how to take care of whatever type of wound you have.

Activity and Follow-up
You should plan on decreased activity and restrict travel for 1 week, and in some cases longer. This is important in order to minimize the scar from spreading and to reduce the chances of bleeding. In some cases where the wound is on the legs, you may be placed on crutches. You will be asked to follow up in 1 to 2 weeks and may subsequently need more follow ups.


Portland Dermatology Clinic encourages new patients to complete our patient forms electronically through our Patient Portal prior to their scheduled appointment. For access to our secure Patient Portal, please call our office at 503-223-3104. If you are unable to complete the forms electronically, you may print our Surgery Welcome Kit and bring it completed to your surgical appointment. 


Click for Caring for Sutured Wound instructions.

Click for Caring for Open Wound instructions.


Click for FAQs (frequently asked questions) about Mohs surgery.


Most insurance carriers cover the cost of Mohs surgery and reconstruction. Please bring your current insurance cards and photo ID with you to each visit. If prior authorization or referral is required, please contact your insurance company or your primary care physician at least one week prior to your appointment.

Click for our clinic's insurance information and financial policy.

Click for Billing FAQs.

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