LITERATURE UPDATE


Exogenous artefacts can interfere with accurate histologic tissue evaluation on frozen sections during Mohs micrographic surgery. Mohs surgeons should be aware of these anomalies to avoid potential misdiagnoses


models trained on permanent pathology is by applying them to frozen sections and fine-tune based on weaknesses. The aim of this study is to qualitatively evaluate a deep learning model trained on permanent pathology to classify squamous cell carcinoma on Mohs surgery frozen sections to learn model shortcomings and inform retraining and fine-tuning.


The authors trained a model for classification of tumour on 746 skin biopsy slides and tested it on 15 Mohs surgery frozen sections. The authors estimated performance metrics and compared the regions of interest generated by the model with the original H&E slides. The model achieved an AUC-ROC of 0.985 and 0.796 for tumour classification in permanent pathology and in frozen sections, respectively. Regions of interest for frozen sections with scarce tumour areas were inaccurate, focusing on normal tissue for slides classified as false negative, or highlighting structures different from tumour (eg, inflammation, muscle, and nerves) for slides classified as true positive.


In conclusion, deep anatomical


structures more commonly present in Mohs frozen pathology might represent data out-of-distribution for models trained on permanent pathology, potentially leading to inadequate model outputs.


Mohs micrographic surgery in the surgical treatment paradigm of melanoma in situ and invasive melanoma: A clinical review of treatment efficacy and ongoing controversies Shah P, Trepanowski N, Grant-Kels JM, LeBoeuf M. J Am Acad Dermatol. 2024 Sep; 91 (3): 499-507. doi: 10.1016/j. jaad.2024.05.024.


Mohs micrographic surgery (MMS) for treatment of melanoma offers several advantages over wide local excision (WLE), including complete histologic margin evaluation, same-day resection and closure, and sparing of healthy tissue in critical anatomic sites. Recently, a large volume of clinical data demonstrating efficacy in MMS


treatment of melanoma was published, leading to emerging patient safety considerations of incurred treatment costs, risk of tumour upstaging, and failure of care coordination for sentinel lymph node biopsy (SLNB). MMS offers a safe, effective, and value-based treatment both for melanoma in situ (MIS) and invasive melanoma (IM), particularly with immunohistochemistry use on frozen sections. Compared to wide local excision, MMS treatment demonstrates similar or improved outcomes for local tumour recurrence, melanoma-specific survival, and overall survival at long- term follow-up. Tumour upstaging risk is low, and if present, alteration to clinical management is minimal. Discussion of SLNB for eligible head and neck IM cases should be done prior to MMS. Though challenging, successful multidisciplinary coordination of SLNB with MMS has been demonstrated. Herein, the authors provide a detailed


clinical review of evidence for MMS treatment of cutaneous melanoma and offer recommendations to address current controversies surrounding the evolving paradigm of surgical management for both MIS and invasive melanoma.


Concordance between a Mohs surgeon and a dermatopathologist in evaluating Mohs cryosections Atilla S, Gököz Ö, Özer S, Elçin G. J Eur Acad Dermatol Venereol. 2021 Nov; 35 (11): 2219-2224. doi: 10.1111/jdv.17574.


Mohs micrographic surgery is the gold standard treatment for high-risk non- melanoma skin cancers. The success of Mohs relies on accurate histopathologic evaluation. Due to law restrictions in some European countries, Mohs surgeons are not permitted to report on histopathology; therefore, a pathologist evaluates the frozen sections. This study aims to retrospectively assess the concordance between the certified Mohs surgeon and the pathologist in evaluating the Mohs slides that were intraoperatively evaluated by the pathologist. Frozen section slides of a total of 237 Mohs cases between 2013 and 2020


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were examined by the blinded Mohs surgeon, and the tumours were marked on copy maps. The copy maps and the original maps were compared, and the non-concordant cases were re-evaluated together by the Mohs surgeon and the dermatopathologist. The concordance rate was calculated, and the inter-rater agreement was statistically analysed using Cohen’s Kappa coefficient. The authors report a high concordance rate (97.9%) and inter-rater agreement (0.96) between Mohs surgeon and dermatopathologist in evaluating Mohs slides.


In conclusion, as a newly settled


centre, the results presented are in alignment with experienced centres where the Mohs surgeon evaluates the slides and performs the surgery.


Histologic Hitchhikers: A Review of Common Exogenous Artifacts Encountered During Mohs Micrographic Surgery


Lam C, Shamloul N, Samaan C, Ken K, Ioffreda M. Dermatol Surg. 2024 Oct 1; 50 (10): 898-903.


doi: 10.1097/DSS.0000000000004233.


Exogenous artefacts can interfere with accurate histologic tissue evaluation on frozen sections during Mohs micrographic surgery (MMS). Mohs surgeons should be aware of these anomalies to avoid potential misdiagnoses. This study reviews exogenous artifacts encountered in frozen tissue pathology during MMS. A literature search was conducted in PubMed to identify studies reporting on exogenous artefacts encountered during MMS and a list of previously described exogenous artefacts was compiled. A retrospective examination of frozen histology slides from recent Mohs cases at the authors’ institution was performed to obtain illustrative examples of these artefacts, supplemented by formalin-fixed paraffin-embedded samples when frozen examples could not be found. Exogenous artefacts represent


foreign bodies that have been externally introduced into the skin or artefacts resulting from other external factors. If frozen section evaluation is inaccurate, overdiagnosis can occur during MMS, resulting in unnecessary layers, larger margins, and more complex reconstructions. These exogenous tissue changes can mimic inflammatory processes and melanocytic or keratinocyte malignancies on histopathology.


In conclusion, exogenous artefacts


are common findings during margin assessment in Mohs micrographic surgery.


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