Mohs Micrographic Surgery: From Layers to Reconstruction (eBook)

1Mohs Micrographic Surgery

Abstract

The two major goals of Mohs micrographic surgery (MMS) are to provide the highest possible cure rate for the treatment of cutaneous malignancies while also ensuring that the malignancy is removed in the most conservative or tissue-sparing manner possible. While these two tenets of this procedure seem straightforward, there is a considerable amount of attention to detail and process quality that is required to provide the service patients expect from MMS. In this chapter, we outline processes and techniques that will lead to successful, reproducible execution of the MMS.

Keywords: Mohs surgery, micrographic surgery, skin cancer treatment, tissue sparing, complete circumferential peripheral and deep margin assessment, initial Mohs stages/layers, subsequent Mohs stages/layers, process improvement

1.1 Before the First Stage

Nicholas Golda and George Hruza

1.1.1 Tumor Selection

Mohs micrographic surgery (MMS) is best suited for the treatment of malignancies that grow in a contiguous manner, meaning that they grow in a manner where the entirety of the tumor is part of a singular mass with no part being physically separated from the primary site of growth. Properly trained providers most commonly use MMS for the treatment of all subtypes of basal cell carcinoma (BCC) and cutaneous squamous cell carcinoma (cSCC), but the procedure is also commonly used for nearly all cutaneous adnexal malignancies—dermatofibrosarcoma protuberans (DFSP), cutaneous leiomyosarcoma, extramammary Paget’s disease (EMPD), atypical fibroxanthoma (AFX), melanoma in situ (MMIS), and, in some cases, for invasive melanoma, Merkel cell carcinoma (MCC), and other far less common cutaneous malignancies.1 The unifying feature of all malignancies treated successfully with MMS is that these tumors are contiguous, thereby allowing the surgeon to detect the totality of the microscopic, often subclinical, extent of the tumor while properly carrying out the procedure.1

Selection of the most appropriate treatment is very important for producing the best results for the patient. While MMS may be utilized for nearly all forms of cutaneous malignancy, it is important to be discerning with respect to which malignancies are treated with the procedure as there are several other alternatives for the treatment of skin cancer beyond MMS, each with its own merits and drawbacks. MMS, while not a more aggressive or arduous procedure for the patient when compared with a standard excision, is a labor-intensive procedure for the physician and the MMS team, often consisting of several individuals in addition to the physician including nurses and histotechnicians. Acknowledging this, MMS is often reserved for malignancies with any of the following features:

•Malignancies in which there is risk of disfigurement or functional loss, such as those on the head and neck, hands, feet, and genitalia.

•Malignancies that have recurred or have been incompletely treated with other treatment modalities.

•Malignancies in immunosuppressed patients, particularly for cSCC in chronic lymphocytic leukemia (CLL) and solid organ transplant patients.

•Large malignancies in any body site.

•Malignancies in patients in whom the tumor border is poorly defined, often due to severe background actinic damage or subclinical tumor growth that may occur, for example, in infiltrating tumors.

•Malignancies exhibiting aggressive growth features clinically and histologically.

•Malignancies in sites where healing is challenging and a maximally conservative technique will reduce the burden of wound healing for the patient, such as in previously irradiated fields and on the legs in patients with peripheral vascular disease or diabetes.

In an effort to create a decision aid for determining which malignancies are appropriate for treatment with MMS, the American Academy of Dermatology convened a task force to develop MMS Appropriate Use Criteria (AUC). The AUC is a publicly available guideline intended to assist physicians with medical decision-making. As a decision aid, it is not intended to replace the judgment of a treating physician in consultation with their patients. Further, it is not intended to establish a standard of care for the treatment of skin cancer as not all tumors deemed appropriate by this system must be treated with MMS, and, conversely, there are situations where the system may deem MMS inappropriate for a particular tumor, while the treating physician, taking into account additional clinical information not accounted for in the AUC, may make the decision to treat with MMS. It should also be noted that the AUC criteria are in constant evolution and are influenced not only by considerations of what is best for the patient but also by economic forces in the health care system at large.

When selecting the most appropriate treatment for skin cancer, it is important to also recognize that a skin biopsy, particularly because of its superficial nature, can misrepresent the true nature of a skin cancer. It has been shown that while carrying out definitive treatment for skin cancer, the skin biopsy underrepresented the aggressive nature of a skin cancer in up to 33% of cases, while tumors were revealed to be less aggressive than the biopsy in 17% of cases.2 Further, tumors that are not amenable to completion of treatment under local anesthesia will be challenging to complete in the outpatient setting with MMS, but MMS can be used in many of these cases as a component of multidisciplinary care for particularly advanced skin cancers such as those invading bone, foramina of the skull, or the orbit. Therefore, the clinician’s judgment, taking into sum all patient factors including clinical and possible radiologic examination, pathologic correlation with that examination, and a discussion with the patient about their goals for treatment, is still the best tool for selecting a plan for skin cancer management.

1.1.2 Documentation of Site

Cure rates are higher when the procedure is done in the correct location. It seems obvious, but in patients with small lesions or significant background actinic damage, or when anatomically inaccurate verbiage is used to describe the original biopsy site, it can, at times, be difficult to identify the correct site for surgery. Further, patients are often unable to accurately recall the correct site of a biopsy, with one study showing the rate of misidentification of the biopsy site by patients at 16.6%.3 It is therefore important to have a clearly defined process for identifying the correct site for surgery. Utilizing photography from the time of biopsy is a best practice for avoiding wrong site surgery.3 Photographs at the time of a skin biopsy should have the planned biopsy site clearly marked and should be taken from far enough away to include anatomic landmarks that can facilitate localizing the site when surgery is eventually carried out. One HIPAA (Health Insurance Portability and Accountability Act of 1996) compliant and relatively simple way to accomplish biopsy site photography is to take a picture of the marked biopsy site with the patient’s mobile phone and ask them to bring their phone with them to their surgical visit if the biopsy reveals a malignancy requiring further treatment.4,​5

In addition to utilizing photography, or when no photograph of the biopsy site is available, providers can use their clinical judgment to identify the biopsy site with confirmation by the patient using a mirror or a photograph on a tablet. Family who are present with the patient, particularly those who have assisted the patient with wound care for the biopsy site, can also be a resource for confirming the correct location for surgery.

If the correct site cannot be confirmed, the surgeon is left with a few options. First, the procedure can be cancelled with the patient returning to the referring provider for site confirmation or monitoring. Alternatively, a frozen section biopsy can be obtained from the most likely candidate location with definitive treatment being done on the same day if the biopsy confirms a skin malignancy. A frozen section biopsy can be carried out by obtaining a biopsy by any technique the surgeon feels will not adversely affect the subsequent definitive procedure if the biopsy is positive and will yield a cosmetically appropriate wound if the site is found to be free of cancer. The biopsy specimen is then processed by vertical sectioning (rather than the tangential sectioning typical of MMS) through the center of the biopsy specimen, stained, and interpreted to confirm the presence or absence of malignancy.6

Occasionally, there is an obvious biopsy site or obvious residual tumor with adjacent skin that is clinically suspicious for being involved by skin cancer but not definitely involved. In these cases, we...