Mohs Surgery

by Verónica Ruiz

MOHS SURGERY: What does it consist of and when is it appropiate to perfom it?

I would like to thank Dr Garces for the opportunity to work with him, being able to start my Mohs surgery training.


What is Mohs surgery?

Mohs micrographic surgery (MMS) was developed by the American surgeon Frederik Mohs in the 1930’s to remove skin tumors so that the entire margins of the part removed under the microscope could be studied.

It is a surgical technique designed for the specific treatment of certain types of skin cancer and in certain body locations, especially on the face.

Is is based on 2 main fundamentals:

  1. Complete tumor exeresis, usually performed in a single procedure, in 1 or several stages.
  2. Microscopic confirmation of the margins of the tumor part removed during the surgery, so that the surgeon and/or pathologist can assess the precise location of possible tumor cases.

” To practice Mohs surgery it is necessary to be familiar with surgical technique and to have knowledge about histopathology and tumor biology; for these reasons, the dermatologist is in a privileged position to be able to perform this technique correctly”.   


What does this technique consist of?

In most cases, MMS is performed in an outpatient basis under local anesthesia, without the need for hospital admission; however, in certain cases, such as complex tumors, or at the request of the patient, general anesthesia will be required.

The 3 fundamental steps in performing the correct technique are:

  • Excision by tangential cut (with the scalpel at 45º) of cutaneous tumors in planes or layers and in successive stages.
  • With this, it is possible to control all the surgical margins (both in the periphery and in depth) of the piece in question, until the entire tumor is eliminated. Processing of the entire excised sample using specific instruments, which allows the piece to be treated appropriately for further study. 
  • Microscopic examination of the processed tissue.

At the end of each stage we will know if the tumor has been completely removed or if there is a persistence of tumor, in which case it will be necessary to carry out a new stage and so on until the tumor removal is complete.

“Mohs surgery allows the study of the entire excised sample in stages until complete tumor excision is achieved, which is achieved, in most cases, in a single intervention and under local anesthesia”.


What benefits or advantages does Mohs surgery provide compared to conventional surgery?

The CMM has some main advantages that are the following:

  • Achieve maximum efficiency (98%-99%) in the removal and complete cure of the tumor, with the aim of minimizing the rate of recurrence and / or tumor persistence.
  • Preserve as much healthy tissue as possible, especially in those anatomical areas where it is essential to maintain a good functional and cosmetic result, such as the face, thus obtaining potentially smaller scars.


What patients are candidates for CMM?

Most of the tumors treated with MSCs fall within the category of non-melanoma skin cancer, the most frequent being basal cell carcinoma and superficial forms dermatofibrosarcom a protuberans;  However some cases of squamous cell carcinomas, and microcystic adnexal carcinoma among others, which can also be successfully treated by CMM.

The main circumstances that we must take into account when correctly indicated a MMS are the tumor location, the characteristics of the tumor (such as the tumor type and the tumor margins) and those related to the patient itself (for example, previous treatments on that specific tumor).

MMS should be considered in the following situations:
  1. Basal cell carcinomas of the facial region and superficial forms of dermatofibrosarcoma protuberans.
  2. Tumors located in other areas, apart from the face, where it is necessary to preserve local functionality / aesthetics such as the nail unit, fingers, genitalia and perianal area.
  3. Poorly delimited tumor margins.
  4. Persistent and / or recurrent tumors after previous treatments.
If Mohs surgery has the best cure rate for non-melanoma skin cancer, why aren’t all skin cancers eliminated with Mohs surgery?

Multiple treatments are available for skin cancer, including topical chemotherapy creams, photodynamic therapy, conventional surgery and radiation therapy. Each tumor and context are different, but by making an adequate selection of treatment for each situation, the healing rates are very high.

“The proper selection of the treatment for each tumor and each patient represents the key to therapeutic success”.

Final summary:

The MMS is a specific technique for the treatment of certain tumor types that allows maximum therapeutic efficiency (close to 100%) to be achieved while preserving as much healthy tissue as possible. Sometimes the choice between having MBC versus other alternative therapies is difficult to make, so your specialist can assist you in evaluating your injury, and help you decide if MBC is right for you.



  • Robert S Stern. Cost effectiveness of Mohs micrographic surgery. J Invest Dermatol 2013 May;133(5):1129-31.
  • Kyle A. Prickett; Michael L. Ramsey. Mohs Micrographic Surgery. StatPearls Publishing; 2020 Jan.
  • Emily P Tierney, C William Hanke. Cost effectiveness of Mohs micrographic surgery: review of the literature. J Drugs Dermatol 2009 Oct;8(10):914-22.