Mohs Micrographic Surgery

Appropriate Use Criteria

In 2012, there was a multi-society collaboration to develop appropriate use criteria (AUC) for MMS . A panel of Mohs surgeons and medical dermatologists analyzed 270 clinical scenarios in which the tumor locations ( Fig. 150.2 ), sizes, and histologic features varied as did whether or not the tumor was recurrent. The purpose of the Mohs surgery AUC was to provide guidance in the rational use of MMS and to identify tumors (e.g. actinic keratoses, superficial BCCs on the trunk) that did not require MMS treatment . The Mohs surgery AUC are available via a dedicated website ( www.aad.org/education/appropriate-use-criteria/mohs-surgery-auc ) as well as the Mohs AUC app. Additionally, one can refer to NCCN guidelines for the treatment of cutaneous malignancies .

Cost-Effective Care

With the escalating cost of medical care, it is important to be attentive to the appropriate use of therapies and knowledgeable regarding the evidence upon which they are based. The studies on the cost effectiveness of MMS have produced variable results and conclusions, depending on the study location and methods . However, application of the Mohs surgery AUC should lead to greater cost-effectiveness. When standard excision with FFPE sections and immediate repair is compared with MMS, the cost differential is comparable or slightly less expensive with the former (standard excision with immediate repair). However, MMS is considered a cost-effective skin cancer treatment when the following factors are taken into account: the physical location of the surgical procedure (office-based versus ambulatory surgery center), the manner in which the specimen is processed (frozen versus permanent), the type of reconstruction (primary/second intention versus flap/graft) based on the size of the defect due to tissue-sparing versus wide local excision, and the need for additional surgery for tumor recurrences .

Basal Cell Carcinoma

For primary BCCs, cure rates of 87% to 95% can be obtained with superficial ablative therapies and excision, especially on the trunk and extremities. In the meta-analysis by Rowe et al. , the 5-year cure rate for primary BCC treated with MMS was 99%, as compared to 90% to 93% using standard treatments ( Table 150.3 ). For recurrent BCC treated with MMS, the 5-year cure rate was 90–94% as compared to 80% for standard treatments (surgical excision, radiotherapy, cryotherapy, electrodesiccation and curettage) .

In addition, MMS provides superior cure rates for high-risk BCCs, including those that are large in size (>2 cm) or have aggressive histologic subtypes or perineural invasion . For example, large BCCs have generally been present for long periods of time and are at greater risk for recurrence, especially if treated with standard methods. When large lesions are present in cosmetically important areas, the sparing of normal tissue is also a critical advantage of MMS. Lastly, basosquamous cell carcinoma, a hybrid between basal and squamous cell carcinoma, has a high risk of local recurrence and is also well managed with MMS .

Squamous Cell Carcinoma

When compared with other treatments, MMS offers the highest cure rates for patients with high-risk primary or recurrent SCCs. The local recurrence rates, based on a retrospective review of MMS versus non-MMS modalities for primary SCC, are outlined in Table 150.3 .

MMS is indicated for management of SCCs with one or more risk factors for recurrence or metastasis (see Table 150.1 ). These indications include large SCCs (>2 cm), recurrent tumors, incompletely excised SCCs, and tumors with ill-defined clinical margins, rapid growth, an aggressive histologic subtype, and/or perineural invasion ( Fig. 150.3 ), as well as SCCs arising in chronic scar tissue . The latter, termed Marjolin ulcers, can behave aggressively, and a multidisciplinary approach with regional node assessment and reconstruction may be necessary in these patients. Numerous, rapidly arising SCCs may affect immunosuppressed solid organ and hematopoietic stem cell transplant recipients or individuals with chronic lymphocytic leukemia, and MMS is well suited for the management of these neoplasms.

In addition, SCC arising in high-risk anatomic sites may be managed with MMS. For example, tumors of the lip have a high propensity for recurrence and metastasis, and cure rates as high as 92% have been obtained with MMS . MMS is also well suited for SCCs occurring in anogenital areas and on the digits, where tissue conservation is important. When compared with conventional methods, MMS for the treatment of penile SCC offers comparable survival rates. Prior to MMS, SCCs involving the nail unit were often treated with amputation or radiation. MMS provides an excellent choice for treatment of periungual and subungual SCC without osseous involvement, with cure rates of up to 96% .

Erythroplasia of Queyrat

Erythroplasia of Queyrat (EQ) is a term for SCC in situ confined to mucosal epithelium. In men, an erythematous thin plaque is typically seen on the inner surface of the foreskin, glans penis, and/or coronal sulcus (see Chs 73 & 108 ). Of note, EQ is seen primarily in uncircumcised men. In women, mucosal SCC in situ favors the labia minora and the vestibule. Oncogenic human papillomaviruses often play an etiologic role, and immunosuppressed individuals (e.g. HIV-infected) are at greater risk for developing anogenital SCC in situ .

MMS is an effective treatment for EQ, with a 5-year cure rate of 90% . When excising EQ of the glans penis, Mohs layers should be very thin in order to minimize entry into and resection of the corpus spongiosum and cavernosum. If either is entered, achieving hemostasis can be challenging. EQ can often extend into the urethra and differentiation of SCC in situ from transitional epithelium is often difficult on frozen sections. With deep extension along the urethra, collaboration with a urologist and completion of the surgery under general anesthesia are recommended.

Keratoacanthoma

Keratoacanthoma (KA) may be considered a well-differentiated SCC with specific histologic features. KAs classically grow quickly and then spontaneously involute; however, there are exceptions and metastasis has been reported, implying that the tumor was actually an SCC. Also, microscopically, some KAs may be difficult to distinguish from an SCC. As a result, nowadays, most KAs are considered to be well-differentiated SCCs and are managed with excisional surgery or MMS. MMS may be particularly beneficial for large lesions, as well as those occurring in anatomically sensitive areas. In one study, a 2-year cure rate of 97.5% was observed for KAs treated via MMS (see Table 150.2 ) .

Verrucous Carcinoma

Verrucous carcinoma is considered a variant of SCC, and it can be triggered by the human papillomavirus. It occurs most commonly in the oral cavity, on the plantar surface of the foot, or on the penis (see Ch. 108 ). While generally considered a low-grade carcinoma, there are reports of metastasis. Because the tumors are usually localized, MMS is an excellent treatment option. Histopathologic interpretation of frozen sections can be challenging because the tumor cells are very well differentiated and lack nuclear atypia, making distinction from epithelial hyperplasia, verruca vulgaris, or condyloma acuminatum difficult.

Lentigo Maligna

Since lentigo maligna (melanoma in situ of sun-damaged skin) may be a clinically and histologically ill-defined tumor, it has a high local recurrence rate with standard wide-excisional surgery. Although frozen section histology of lentigo maligna can be challenging, MMS offers the possibility of complete margin examination and tissue sparing. Immunohistochemical (IHC) staining of frozen sections (see below) may improve diagnostic accuracy . Because of the challenge of detecting atypical melanocytes in frozen sections, some surgeons employ techniques such as wide excision Mohs surgery, “slow” Mohs staged excision (utilizing FFPE sections), and geometric staged excision (see Variations) .