Mohs micrographic surgery (MMS) is named after Frederick Mohs, who pioneered this technique. His original chemosurgery procedure has been modified to a fresh frozen tissue technique.
In Australia the Australian College of Dermatologists (ACD) maintains the register of physicians who can claim the Mohs Medicare item number. The ACD is responsible for training, accreditation and ongoing professional requirements to remain on the Mohs register. The ACD also sets Appropriate Use Criteria for the Mohs surgery and Clinical Benchmarks, which have been adopted by Medicare. It is undertaken in several specialised centres in Australia and is primarily used in a tertiary referral setting for difficult-to-treat tumours.
Mohs surgery is usually performed under local anaesthetic. Following excision of the tumour, almost the entire peripheral and deep margins of the excised tissue are examined by frozen section (see Figure 1). In contrast, standard sectioning used by pathologists may examine only 0.1–1.0% of the surgical margin.
The MMS technique, through a combination of specialised tissue processing and mapping ,allows precise localisation of residual tumour. It aims to ensure complete tumour clearance while maximising normal tissue conservation and function. The technique is based on the principle of contiguous tumour growth. Previous treatment by breaking up a tumour can limit its effectiveness. Furthermore, the suitability of a tumour for frozen section analysis is an important part of case selection.
An advantage of MMS is that the proceduralist removing the tumour also examines the histological slides, thus eliminating the communication errors that can occur in a multidisciplinary approach.
The procedure requires specialised equipment and staff. Each excision takes 5–30 minutes and the processing and reading of stained frozen sections takes from 15 minutes to one hour. The total procedure may take up to several hours depending on the size and complexity of the specimen. The technique requires specific training and expertise, both for the MMS proceduralist and also for the assisting technicians.
Mohs surgery is becoming increasingly available and therefore it is important that medical practitioners treating skin cancer know about it. It is a highly specialised technique required for a small number of tumours that fit specific criteria, the decision to offer MMS should be by a medical practitioner experienced in skin cancer diagnosis and management who has a clear understanding of the technique and its value.
Overview of evidence (non-systematic literature review)
The criteria for choosing Mohs over other techniques include scenarios where a clear advantage in tumour cure are present and/or where the tissue sparing capacity of the technique would be significant.
A systematic review and meta-analysis reported a significantly reduction in 5-year recurrence rate with MMS compared with standard excision for recurrent high-risk facial basal cell carcinoma (BCC). The study was unable to make a conclusion for other types of BCC and SCC.
A RCT conducted over 10 years in the Netherlands compared MMS with standard excision for primary and recurrent facial BCC. The final analysis showed a lower 10‐year recurrence rate with MMS for high risk facial BCC when compared with standard excision. However, the difference in recurrence rates was only statistically significant for recurrent tumours. A high proportion of recurrences occurred after more than 5 years’ follow-up. The study findings emphasise the long follow-up required for some facial BCCs. More research is required in this area, particularly with regard to high-risk primary facial BCCs.
There are no RCTs comparing MMS and wide excision for the treatment of SCC to date. There is lower level evidence (2a and 2b) which supports the use of MMS for the treatment of SCC.
- MMS achieves a superior cure rate than wide excision for high-risk recurrent BCC of the face
- MMS and wide excision achieve similar cure rates for primary BCC of the face
- MMS and wide excision achieve similar cure rates for the management of cSCC of the face.
Available data support the argument that, across a variety of clinical scenarios for BCC excision, MMS may reduce the defect area compared with wide excision. Whether this is important in a clinical scenario is unknown. Smaller defects do not always lead to easier reconstruction or repair.
PP 7.8.1. Mohs micrographic surgery may also be considered as an alternative to wide surgical excision in the following types of basal cell carcinoma:
- Surgical treatment – Introduction
- Considerations before selecting a surgical treatment modality
- Optimal primary excision techniques
- Optimal surgical technique for the treatment of basal cell carcinoma
- Considerations when planning surgical treatment for cutaneous squamous cell carcinoma
- Post-surgical care, interpretation of the pathology report and follow-up
- Protocol to manage incompletely resected basal cell carcinoma
- Management protocol for rapidly growing tumours
- Surgical management of advanced cutaneous squamous cell carcinoma
- Surgical treatment – Health system implications and discussion
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