An Australian Mohs external quality assurance program

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Peck, Martyn
Yiasemides, Eleni
Badrick, Tony
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Background: Mohs micrographic surgery (MMS) has been shown to be an effective treatment for non‐melanoma skin cancer.1 Squamous cell carcinoma (SCC) and basal cell carcinoma (BCC) are the most common type of skin cancers worldwide with an increasing incidence in both men and women. Treating SCC and BCC, together make up the greatest cost of cancer treatment in Australia: an estimated total of $AU345 million per year.

MMS provides distinct advantages over traditional excisional surgery. It offers tissue‐sparing treatment of cutaneous neoplasms with a higher cure rate; 99% for primary BCC and 97% for primary SCC,2 and has been shown to be cost‐effective compared to traditional excisional surgery.3-5

The MMS technique involves mapping and staining the excised tissue and a specialised tissue sectioning process that enables visualisation of virtually all tissue margins and the precise localisation of any residual tumour. If any residual tumour is detected, the above process is repeated until the margin is tumour‐free. The resulting defect is then ready for repair as appropriate for the particular site. A key component of Mohs surgery is that the Mohs surgeon removing the tumour also examines the histological slides, thus eliminating the communication errors that can occur in a multidisciplinary laboratory approach.

Therefore, the success rate of this procedure is dependent on the accurate microscopic evaluation of carefully mapped specimens. The Mohs surgeon must be able to translate abnormal findings on the tissue map into appropriate sequential tumour removal.6 A critical component of the technique is the surgeon's skill in interpreting histological specimens, and yet few studies have analysed Mohs surgeons’ capacity to read frozen sections.7

A small number of published studies have investigated the concordance of Mohs surgeons’ interpretation of frozen sections with that of dermatopathologists. The published concordance rates have been very high, i.e. above 95%.7-9 Nevertheless, no formal external quality assurance program (EQA) assessing the Mohs surgeon's diagnostic accuracy of interpreting frozen section existed in Australia previously.

In 2012 the Mohs surgeon group was formed as a specialist subgroup of the Australasian College of Dermatologists (ACD). Part of the group's aim was to establish formal EQA for diagnostic Mohs frozen sections to maintain acceptable standards for the histological diagnostic capabilities of its Mohs surgeon members. In addition to maintaining standards, the group also aimed to have an educational and continued professional development aspect as well as to create a teaching library of Mohs frozen section slides.

The American College of Mohs Surgeons (ACMS) has successfully run a diagnostic quality control exam on a frozen section dermatopathology program. Initially this was run annually at the ACMS annual scientific meeting, with physical slides and microscopes set up for members to undertake the program. In 2014 the ACMS ran their program for the first time as entirely computer based with virtual images.

At its 2014 Annual Advisory Committee meeting the ACD Mohs surgeon group decided to establish its own diagnostic frozen section program. Hence, it was decided that an external and independent quality assurance program would be set up in conjunction with the well‐established Royal College of Pathologists Australia Quality Assurance Program (RCPAQAP). This alliance aimed to create an independent assessment of the proficiency testing in a professional and truly unbiased manner. In addition, the alliance allowed for a cost‐effective program that would be completely computer based from its inception, i.e. the pilot Mohs module for the purpose of EQA.

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Australasian Journal of Dermatology

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Peck, M; Yiasemides, E; Badrick, T, An Australian Mohs external quality assurance program, Australasian Journal of Dermatology, 2018, 59 (2), pp. E138-E142