Indications defined by the American Academy of Dermatology (AAD) include basal cell carcinomas (BCC) and squamous cell carcinomas (SCC) of the "mask area of the face," cheeks, and forehead (Connolly, J Am Acad Dermatol, 2012).
- The decision to choose the Mohs technique versus intraoperative histopathologic examination is multifactorial, including patient preference, surgeon comfort, location of the lesion, availability of a Mohs surgeon, and availability of a pathologist to perform frozen section evaluation.
- The Mohs technique allows for assessment of circumferential skin and deep tumor margins in a horizontal plane.
- Excision of periocular BCC and SCC, and monitoring of surgical margins, might require more than the horizontal orientation afforded by the Mohs technique, necessitating additional histopathologic assessment for 3D orientation of tumor planes.
- For example, tumors that invade the orbit require additional histopathology to assess the degree of orbital invasion.
- Lid margin basal cell and squamous cell carcinoma may be assessed by the Mohs technique; alternatively, wedge excision might be preferred, with histopathologic assessment of the surgical margins on either side of the lesion and at the base of the specimen.
- Medial canthal tumors can ideally be studied by the Mohs technique.
- Deep invasion beyond the surface of the skin requires histopathologic evaluation beyond the Mohs technique; specifically, if the tumor extends into vital structures and surgical resection with local anesthetic is not possible, Mohs micrographic resection is an unacceptable treatment option (Nehal, Elsevier, 2014).
Lentigo maligna and malignant melanoma in-situ, which can be removed by the Mohs technique according to AAD guidelines, require permanent histopathology because frozen section processing ruptures melanocytes.
Malignancies which are more difficult to eradicate locally, such as leiomyosarcoma, apocrine/eccrine carcinoma, Merkel cell carcinoma, mucinous carcinoma, and sebaceous carcinoma, require wider surgical margins, beyond histopathologically confirmed tumor free margin, and the Mohs technique might be inappropriate for these tumors.
Contraindications to the Mohs technique include periocular malignant melanoma, which requires permanent sections to ensure complete resection, and orbital tumors.