Frozen-Section Tissue Processing in Mohs Surgery

Intraoperative margin assessment for basal cell carcinoma with deep learning and histologic tumor mapping to surgical site

Successful treatment of solid cancers relies on complete surgical excision of the tumor either for definitive treatment or before adjuvant therapy. Intraoperative and postoperative radial sectioning, the most common form of margin assessment, can lead to incomplete excision and increase the risk of recurrence and repeat procedures. Mohs Micrographic Surgery is associated with complete removal of basal cell and squamous cell carcinoma through real-time margin assessment of 100% of the peripheral and deep margins. Real-time assessment in many tumor types is constrained by tissue size, complexity, and specimen processing / assessment time during general anesthesia. We developed an artificial intelligence platform to reduce the tissue preprocessing and histological assessment time through automated grossing recommendations, mapping and orientation of tumor to the surgical specimen. Using basal cell carcinoma as a model system, results demonstrate that this approach can address surgical laboratory efficiency bottlenecks for rapid and complete intraoperative margin assessment.

An international survey characterizing Mohs tissue processing techniques and Mohs margin thresholds: how close is too close?

BACKGROUND

From practice, we identified heterogeneity in Mohs micrographic surgery (MMS) specimen tissue processing techniques and specifications, and in the Mohs surgeons' assessment of MMS specimen histological tumour clearance.

AIM

By surveying an international cohort of Mohs surgeons, we determined to characterize variation in margin threshold assessment (number of wafers/sections free of tumour to declare tumour clearance).

METHODS

An online questionnaire was distributed to Mohs surgeons in the UK, European countries, Australia and New Zealand, assessing the background demographics of the surgeons and the technical factors involved in MMS tissue processing and posing three MMS scenarios to define margin thresholds.

RESULTS

In total, 114 consultant/attending-level Mohs surgeons responded, giving a response rate of 33.5% from 20 countries (including UK nations). The first scenario posed was a 20-mm cheek basal cell carcinoma (BCC) excised by MMS with a fully complete first wafer (7 μm) clear of tumour and the second wafer (after trimming interval of 50 μm) demonstrating a small dermal focus of nodular BCC; of the 58 surgeons, 16 (27.6%) would not take another stage. With a follow-up question, 16 of the 58 (27.6%) surgeons specified wanting three clear sections to declare tumour clearance. When the same scenario had a change to a 20-mm infiltrative BCC, 84.2% (48 of 57 surgeons) required a second MMS stage, with a follow-up question clarifying that a third (19 of 57) wanted three clear sections to determine clearance. For a well-differentiated 15-mm squamous cell carcinoma with the same factors there was no majority consensus, with the same proportion of surgeons (22.6%; 12 of 53) calling tumour clearance after one, two and three clear section(s) respectively. For MMS specimen processing specifications, routine sections/wafers of 5-10 μm were reported by 77.4% of respondents (48 of 62) and for trimming interval values, 78.6% (48 of 61) specified a range between 20 and 200 μm.

CONCLUSION

By surveying international Mohs surgeons, we highlight surgeon background characteristics, peer-compare assessment of margin thresholds for tumour clearance across three scenarios, and delineate tissue processing and intraoperative approaches.

A review of the evidence for Mohs micrographic surgery in the treatment of basal cell carcinoma

MMS is considered the gold standard treatment for basal cell carcinoma (BCC) particularly for sites with a high-risk of incomplete excision such as the central face, tumours with an aggressive growth pattern and consequent unpredictable sub-clinical extension and recurrent tumours. However, the process is more time consuming and the magnitude of benefit is uncertain. This article aims to provide a more complete picture of current evidence, including a review of cosmetic outcomes, tissue sparing ability and cost-effectiveness of MMS. Whilst robust evidence is lacking, there is a large volume of observational data supporting a low recurrence rate after MMS. The risk of incomplete excision and higher recurrence rate of standard excision favours the use of MMS at high-risk sites. There is some low certainty evidence that MMS results in a smaller defect size than SE and that incomplete excision with SE results in larger defects. Larger defects may affect cosmetic outcome but there is no direct evidence that MMS improves cosmetic outcome compared to SE. There is conflicting evidence regarding the cost of MMS in comparison to SE with some studies recognising MMS as less expensive than SE and others more which may reflect the healthcare setting. A multi-centre 10 year RCT comparing MMS and SE in the treatment of high-risk BCC would be desirable, but is unlikely to be feasible or ethical. Collection of robust registry data capturing both MMS and SE outcomes would provide additional long-term outcomes.

A review of Mohs Micrographic Surgery for skin cancer: Part 1 - melanoma and rare skin cancers

Mohs micrographic surgery is a precise and effective method commonly used to treat high risk basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) on the head and neck. Whilst the majority of evidence for Mohs relates to keratinocyte cancers, there is published evidence for other types of skin cancer. This review aims to discuss the evidence for using MMS to treat six different types of skin cancer, including melanoma, lentigo maligna, dermatofibrosarcoma protuberans, atypical fibroxanthoma, microcystic adnexal carcinoma and pleomorphic dermal sarcoma, particularly in the context of survival rates and cancer recurrence. These cancers were chosen as there was sufficient literature for inclusion and given MMS is most useful when cancers are contiguous, rather than for cancers with marked metastatic potential such as angiosarcoma or merkel cell carcinoma. We searched Medline, Pubmed and Embase using the keywords: 'melanoma', 'mohs micrographic surgery', 'lentigo maligna', 'dermatofibrosarcoma protuberans', 'atypical fibroxanthoma', 'microcystic adnexal carcinoma' and 'pleomorphic dermal sarcoma' along with their appropriate synonyms, to identify the relevant English-language articles from the year 2000 onwards given that literature for Mohs on non-keratinocyte is sparse prior to this date. A MeaSurement Tool to Assess systematic Reviews (AMSTAR) was used to assess the validity of systematic reviews. Further high-quality, multi-centre randomised trials are necessary to establish the indications and efficacy of MMS for rarer cancers, particularly for AFX and PDS, where limited studies were identified.

Concordance between a Mohs surgeon and a dermatopathologist in evaluating Mohs cryosections

BACKGROUND

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.

OBJECTIVE

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.

MATERIALS AND METHODS

Frozen section slides of a total of 237 Mohs cases between 2013 and 2020 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.

RESULTS

We report a high concordance rate (97.9%) and inter-rater agreement (0.96) between Mohs surgeon and dermatopathologist in evaluating Mohs slides.

CONCLUSION

As a newly settled centre, our results are in alignment with experienced centres where the Mohs surgeon evaluates the slides herself and performs the surgery.

Deep learning automated pathology in ex vivo microscopy

Standard histopathology is currently the gold standard for assessment of margin status in Mohs surgical removal of skin cancer. Ex vivo confocal microscopy (XVM) is potentially faster, less costly and inherently 3D/digital compared to standard histopathology. Despite these advantages, XVM use is not widespread due, in part, to the need for pathologists to retrain to interpret XVM images. We developed artificial intelligence (AI)-driven XVM pathology by implementing algorithms that render intuitive XVM pathology images identical to standard histopathology and produce automated tumor positivity maps. XVM images have fluorescence labeling of cellular and nuclear biology on the background of endogenous (unstained) reflectance contrast as a grounding counter-contrast. XVM images of 26 surgical excision specimens discarded after Mohs micrographic surgery were used to develop an XVM data pipeline with 4 stages: flattening, colorizing, enhancement and automated diagnosis. The first two stages were novel, deterministic image processing algorithms, and the second two were AI algorithms. Diagnostic sensitivity and specificity were calculated for basal cell carcinoma detection as proof of principal for the XVM image processing pipeline. The resulting diagnostic readouts mimicked the appearance of histopathology and found tumor positivity that required first collapsing the confocal stack to a 2D image optimized for cellular fluorescence contrast, then a dark field-to-bright field colorizing transformation, then either an AI image transformation for visual inspection or an AI diagnostic binary image segmentation of tumor obtaining a diagnostic sensitivity and specificity of 88% and 91% respectively. These results show that video-assisted micrographic XVM pathology could feasibly aid margin status determination in micrographic surgery of skin cancer.

Clinical integration of fast Raman spectroscopy for Mohs micrographic surgery of basal cell carcinoma

We present the first clinical integration of a prototype device based on integrated auto-fluorescence imaging and Raman spectroscopy (Fast Raman device) for intra-operative assessment of surgical margins during Mohs micrographic surgery of basal cell carcinoma (BCC). Fresh skin specimens from 112 patients were used to optimise the tissue pre-processing and the Fast Raman algorithms to enable an analysis of complete Mohs layers within 30 minutes. The optimisation allowed >95% of the resection surface area to be investigated (including the deep and epidermal margins). The Fast Raman device was then used to analyse skin layers excised from the most relevant anatomical sites (nose, temple, eyelid, cheek, forehead, eyebrow and lip) and to detect the three main types of BCC (nodular, superficial and infiltrative). These results suggest that the Fast Raman technique is a promising tool to provide an objective diagnosis "tumour clear yes/no" during Mohs surgery of BCC. This clinical integration study is a key step towards a larger scale diagnosis test accuracy study to reliably determine the sensitivity and specificity in a clinical setting.

Mohs micrographic surgery in dermatofibrosarcoma protuberans: Rate and risk factors for recurrence in a prospective cohort study from the Spanish Registry of Mohs Surgery (REGESMOHS) and review of the literature

Characterization of patients, surgery procedures and the risk factors for dermatofibrosarcoma protuberans (DFSP) recurrences is poorly defined. In this study, we aimed to describe the demographics, tumor characteristics and interventions of DFSP treated with Mohs micrographic surgery (MSS) to determine the rate and risk factors for recurrence. Data were collected from REGESMOHS, a nationwide prospective cohort study of patients treated with MMS in Spain. From July 2013 to February 2020, 163 patients with DFSP who underwent MMS were included. DFSP was mostly located on trunk and extremities. Recurrent tumors had deeper tumor invasion and required higher number of MMS stages. Paraffin MMS was the most frequently used technique. Overall recurrence rate was 0.97 cases/100 person-years (95% IC = 0.36-2.57). No differences were found in epidemiological, tumor, surgery characteristics or surgical technique (frozen or paraffin MMS [p = 0.6641]) in terms of recurrence. Median follow-up time was 28.6 months with 414 patient-years of follow-up. In conclusion, we found an overall low recurrence rate of DFSP treated with MMS. None of the studied risk factors, including MMS techniques, was associated with higher risk for recurrence.