Histologic pitfalls in the Mohs technique

Review on the Role of Paraffin-embedded Margin-controlled Mohs Micrographic Surgery to Treat Skin Tumors

Paraffin-embedded margin-controlled Mohs micrographic surgery (PMMS) includes various procedures such as slow Mohs or deferred Mohs technique, the Muffin and Tübingen techniques, and staged margin excision, or the spaghetti technique. PMMS is a variation of conventional Mohs micrographic surgery (MMS) that allows histopathological examination with delayed margin control. PMMS requires minimum training and may be adopted by any hospital. The setback is that PMMS can require procedures across multiple days. PMMS lowers the rate of recurrence of basal cell carcinoma vs wide local excision in high-risk basal cell carcinoma, and improves the rates of recurrence and survival in lentigo maligna. PMMS can be very useful in high-risk squamous cell carcinoma treatment. Finally, it is a promising technique to treat infrequent skin neoplasms, such as dermatofibrosarcoma protuberans, or extramammary Paget's disease, among others. In this article, we present a literature narrative review on PMMS, describing techniques and indications, and highlighting long-term outcomes.

Review on the Role of Paraffin-embedded Margin-controlled Mohs Micrographic Surgery to Treat Skin Tumors

Paraffin-embedded margin-controlled Mohs micrographic surgery (PMMS) includes various procedures such as slow Mohs or deferred Mohs technique, the Muffin and Tübingen techniques, and staged margin excision, or the spaghetti technique. PMMS is a variation of conventional Mohs micrographic surgery (MMS) that allows histopathological examination with delayed margin control. PMMS requires minimum training and may be adopted by any hospital. The setback is that PMMS can require procedures across multiple days. PMMS lowers the rate of recurrence of basal cell carcinoma vs wide local excision in high-risk basal cell carcinoma, and improves the rates of recurrence and survival in lentigo maligna. PMMS can be very useful in high-risk squamous cell carcinoma treatment. Finally, it is a promising technique to treat infrequent skin neoplasms, such as dermatofibrosarcoma protuberans, or extramammary Paget's disease, among others. In this article, we present a literature narrative review on PMMS, describing techniques and indications, and highlighting long-term outcomes.

Cutaneous squamous cell carcinoma characterized by MALDI mass spectrometry imaging in combination with machine learning

Cutaneous squamous cell carcinoma (SCC) is an increasingly prevalent global health concern. Current diagnostic and surgical methods are reliable, but they require considerable resources and do not provide metabolomic insight. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) enables detailed, spatially resolved metabolomic analysis of tissue samples. Integrated with machine learning, MALDI-MSI could yield detailed information pertaining to the metabolic alterations characteristic for SCC. These insights have the potential to enhance SCC diagnosis and therapy, improving patient outcomes while tackling the growing disease burden. This study employs MALDI-MSI data, labelled according to histology, to train a supervised machine learning model (logistic regression) for the recognition and delineation of SCC. The model, based on data acquired from discrete tumor sections (n = 25) from a mouse model of SCC, achieved a predictive accuracy of 92.3% during cross-validation on the labelled data. A pathologist unacquainted with the dataset and tasked with evaluating the predictive power of the model in the unlabelled regions, agreed with the model prediction for over 99% of the tissue areas. These findings highlight the potential value of integrating MALDI-MSI with machine learning to characterize and delineate SCC, suggesting a promising direction for the advancement of mass spectrometry techniques in the clinical diagnosis of SCC and related keratinocyte carcinomas.

Rapid clearing and imaging of Mohs and melanoma surgical margins using a low-cost tissue processor

Tissue clearing methods render biological tissues transparent while maintaining tissue structure, enabling visualization of entire tissues. Recent developments in tissue clearing have predominantly emphasized preserving intrinsic fluorescent proteins or aqueous-based tissue clearing and so typically involve complex procedures and long processing times. The utilization of tissue clearing protocols in standard of care histology settings has been less well explored, and protocols for rapid clearing of human tissue specimens are limited. This study presents a novel rapid clearing protocol and demonstrates a low-cost tissue processor for high volume rapid tissue clearing that can be intergraded into standard histology workflow. We demonstrate rapid clearing in dermatological specimens, including both nonmelanoma and melanoma excisions.

Reported Outcome Measures in Mohs Micrographic Surgery in Studies With Defined Techniques for Embedding and Processing of Tissue: A Systematic Review

BACKGROUND

Mohs micrographic surgery (MMS) is a technique that combines surgical excision and histologic evaluation to achieve higher cure rates for skin cancer than traditional surgical excision. Competing performance measures have fostered numerous histologic techniques for MMS.

OBJECTIVE

To analyze differences in primary outcomes in the published literature regarding the technique of tissue processing and embedding during the MMS process.

METHODS

A systematic review was performed of the published literature in MEDLINE, PubMed, Embase, and Cochrane library that included a description of the manipulation of tissue during the grossing and embedding steps of MMS.

RESULTS

Inclusion criteria were met by 61 articles. Of these studies, the cure/recurrence rate was assessed in 1 article (1.6%), tissue conservation was assessed in 47 (77%), time-saving was assessed in 35 (57%), cost-saving was assessed in 6 (10%), and decreased artifact were assessed in 20 (33%).

CONCLUSION

There is a lack of standardization for assessing clinical outcomes in the published literature regarding MMS process techniques. Cure is a critical outcome in studies comparing MMS processing methodologies.

Slice by slice: An Australian state-by-state analysis of Mohs micrographic surgery over 5 years

BACKGROUND

In November 2018, Mohs micrographic surgery (MMS) was restricted to fellows registered with the Australasian College of Dermatologists. Three new item numbers for the provision of MMS were also introduced. We examine the national and state usage of MMS item numbers based on Medicare claim statistics and Mohs surgeons' self-reported data, noting the impact of the pandemic and the usage of individual item numbers.

METHODS

Medicare item number data were obtained from the Medicare Benefits Schedule website for January 2017-December 2021. Self-reported data were collected on an annual basis by the Royal College of Pathologists of Australasia (RCPA) as part of the Quality Assurance Program (QAP) from 2019 onwards. Data were analysed with the Holt-Winters smoothing method for forecasting.

RESULTS

An increasing number of MMS claims were processed each year, with a total of 89,183 for the study period. Since November 2018, 97.7% of procedures have been conducted on the head, neck, genitalia, hand, digits, leg (below the knee) or foot. The provision of services across the country was maintained during the pandemic years of 2020-2021, with an increase in services in Queensland. There were discrepancies between the states for procedures performed in greater than six sections; these constituted more than 35% of claims in Queensland and Western Australia compared to less than 15% in other states. The pandemic impacted certain states more than others, with Victoria and the Northern Territory having significantly fewer presentations than predicted (p < 0.05).

CONCLUSIONS

Overall, the use of MMS in Australia is in keeping with peer-developed guidelines, despite discrepancies between states. Although certain states were more severely affected by the pandemic, MMS is increasingly used in Australia.

Mohs micrographic surgery: a review of indications, technique, outcomes, and considerations

Mohs micrographic surgery is a specialized form of skin cancer surgery that has the highest cure rates for several cutaneous malignancies. Certain skin cancers can have small extensions or “roots” that may be missed if an excised tumor is serially cross-sectioned in a “bread-loaf” fashion, commonly performed on excision specimens. The method of Mohs micrographic surgery is unique in that the dermatologist (Mohs surgeon) acts as both surgeon and pathologist, from the preoperative considerations until the reconstruction. Since Dr. Mohs’s initial work in the 1930s, the practice of Mohs micrographic surgery has become increasingly widespread among the dermatologic surgery community worldwide and is considered the treatment of choice for many common and uncommon cutaneous neoplasms. Mohs micrographic surgery spares the maximal amount of normal tissue and is a safe procedure with very few complications, most of them managed by Mohs surgeons in their offices. Mohs micrographic surgery is the standard of care for high risks basal cell carcinomas and cutaneous squamous cell carcinoma and is commonly and increasingly used for melanoma and other rare tumors with superior cure rates. This review better familiarizes the dermatologists with the technique, explains the difference between Mohs micrographic surgery and wide local excision, and discusses its main indications.

Commentary on Dermoscopy as a complementary tool for positive margin demarcation on the Mohs' map

Mohs micrographic surgery (MMS) is a technique that allows removal of complex or ill-defined skin cancer, combining tissue preservation and complete microscopic margin control. One of the main challenges of Mohs surgery is to illustrate the exact location of the tumour detected by light microscope. Using a dermoscope allows a fast, easy, reproducible way to accurately illustrate the location of a positive tumour on the Mohs map and ultimately transpose it to the surgical defect of the patient in a more precise way.

Frozen-Section Tissue Processing in Mohs Surgery

BACKGROUND

Mohs micrographic surgery (MMS) is the most reliable tissue-sparing technique in the management of cutaneous malignancies. Although the concept is simple, there is considerable variability in the mapping and processing techniques used by Mohs surgeons and histotechnicians.

OBJECTIVE

This review article aims to examine the frozen-section tissue processing techniques. Existing variations will be discussed and pearls offered to optimize the frozen processing technique.

METHODS

A PubMed search was performed for publications on methods of tissue processing in MMS.

RESULTS

Our review highlights variations in debulking, embedding, processing adipose tissue, cartilage, and wedge resections. We offer pearls on how to avoid false-positive and false-negative margins and discuss advances in immunohistochemistry.

CONCLUSION

Our article provides a how-to format on the different stages of tissue processing with pearls and techniques to optimize practice and improve accuracy.

Horizontal histological sections in the preliminary evaluation of basal cell carcinoma submitted to Mohs micrographic surgery

BACKGROUND

Mohs micrographic surgery is a surgical technique for the treatment of nonmelanoma skin cancer. Surgery begins by removing the visible tumor before excision of the tissue specimens for evaluation of the tumor margins.

OBJECTIVES

To present a new way to evaluate the material obtained from debulking, by horizontal histological analysis of the fragment.

METHODS

Descriptive retrospective cross-sectional study based on the medical records and histological lamellae of patients with primary basal cell carcinomas smaller than 1.5cm submitted to Mohs micrographic surgery and who had the visible tumor analyzed by horizontal histological sections.

RESULTS

The sample evaluated included 16 patients with lesions located on the face. Comparing the histopathological examinations of incisional biopsy in vertical sections and debulking in horizontal sections, there was agreement in seven cases. The histological analysis performed in horizontal sections allowed identification of the tumor site in 13 cases, and the relation between tumor and margin showed that in 11 cases, the lateral margin was compromised.

STUDY LIMITATIONS

The technique was better-applied in lesions smaller than 2cm.

CONCLUSION

Horizontal histological analysis of debulking has advantages for Mohs surgery, since it allows visualization of almost all tumor extension in the same view plane of the dermatoscopy, allowing better definition of the histological subtype, tumor site, and tumor/margin of lesions less than 1.5cm.

Presurgical Curettage Improves Accuracy for Nonmelanoma Skin Cancer Excision

BACKGROUND

Presurgical curettage before nonmelanoma skin cancer surgery may help delineate tumor subclinical extensions.

OBJECTIVE

To determine histologically whether presurgical curettage appropriately or inappropriately changes excision specimen size.

MATERIALS AND METHODS

One hundred fifty consecutive nonmelanoma skin cancers treated with Mohs micrographic surgery. The clinical margin (CM) was marked. Presurgical curettage was then performed and the resultant presurgical curettage margin (PCM) marked. Frozen section analysis of the CM and PCM revealed whether the curettage-induced margin change was appropriate or unnecessary.

RESULTS

Presurgical curettage appropriately increased the surgical margin in 9.3% of cases, reducing the number of Mohs stages from 2 to 1. It appropriately decreased the surgical margin in 17.3% thereby conserving normal skin. In 19.4% of cases the curettage increased the margin in situations where the CM had underestimated the size of the tumor; however, in these cases, the curettage did not increase the margin sufficiently to clear the tumor. In 44.0% of cases the PCM did not change the size of the stage I specimen compared to the CM and confirmed the CM. In 10.0% of cases, preoperative curettage reduced margin accuracy by removing healthy tissue (8.0%) or underestimating tumor (2.0%). These errors were associated with eyelid location, severe background photodamage, and morpheiform/infiltrating/sclerosing basal cell carcinomas.

CONCLUSION

Presurgical curettage can improve tumor excision accuracy and efficiency. Careful tumor selection is important to optimize curette utility.

A single-institution retrospective evaluation of Mohs incision angles and histopathologic specimen quality

BACKGROUND

Traditionally, Mohs layers are excised using a beveled incision to facilitate tissue flattening for tangential sectioning. Some surgeons perform non-beveled incisions; however, these specimens may be harder for the histotechnician to process. Limited data exist comparing slide quality between these techniques.

METHODS

Retrospective review of cases performed by two Mohs surgeons (surgeon 1 = non-beveled incision; surgeon 2 =  beveled incision) using different incision angles between June 2014 and December 2016. Daily histopathologic slide quality assessment scores (maximum score = 5, minimum score = 1) of the day's first case were compared.

RESULTS

About 536 slides (surgeon 1 = 277, surgeon 2 = 259) were evaluated from 2,825 cases. Mean quality assessment scores were similar between surgeons (4.89 and 4.86; P = 0.31) with missing or folded epidermis being the most commonly reported issue for both surgeons.

CONCLUSION

Similar slide quality can be achieved via both beveled and non-beveled Mohs cutting angles. While more relaxing incisions may be necessary to optimize tissue flattening with non-beveled incisions, there is no associated increased loss of epidermal margins. The potential benefits of non-beveled incisions, such as minimizing tangentially cut adnexal structures and creating vertical wound edges optimized for repair, may offer an alternative technique with positive clinical implications.

Histopathologic pitfalls of Mohs micrographic surgery and a review of tumor histology

Mohs micrographic surgery is a specialized subset of staged surgical excisions with each subsequent stage being driven largely by the histologic findings of the previous stage. Therefore, it is imperative that histologic analysis is performed in an accurate manner. Frozen section and tissue flattening is a crucial step in Mohs surgery. Frozen sections introduce certain artifacts and these artifacts must be interpreted in the correct context. Basal and squamous cell carcinomas are the most common tumors encountered in Mohs micrographic surgery, and their histopathology is also associated with certain "pitfalls". Basal cell carcinoma should be distinguished from hair follicles, folliculocentric basaloid proliferations, poromas, nevus sebaceous, desmoplastic trichoepitheliomas, and spiradenomas, to name but a few histologic entities. Similarly, squamous cell carcinoma should be distinguished from hypertrophic actinic keratoses, pseudoepitheliomatous hyperplasia, sebaceous carcinoma, and microcystic adnexal carcinoma. In addition, there are numerous subtypes of basal cell and squamous carcinomas that the Mohs surgeon should be aware of due to differences in the biologic behavior of these tumors. This review presents a number of the common histologic pitfalls of Mohs micrographic surgery and a review of tumor histology.

Reliability of diagnosis from Mohs slides: interpersonal and intrapersonal agreement on basal cell carcinoma presence and histological subtype

BACKGROUND

The success of Mohs micrographic surgery (MMS) depends partly on the correct diagnosis of slides.

OBJECTIVES

To determine reliability of diagnosis from Mohs slides.

METHODS

This was a prospective study evaluating the reliability of diagnosis from Mohs slides of basal cell carcinoma (BCC) presence, BCC location on the slide and BCC subtype among six raters who independently assessed 50 Mohs slides twice with a 2-month interval. Slides were randomly selected whereby difficult-to-diagnose slides were oversampled. For each slide, a reference diagnosis was established by an expert panel. Cohen's kappa (κ) was calculated to determine levels of agreement interpersonally (rater vs. reference diagnosis) and intrapersonally (rater at T1 vs. T2). Multivariable logistic regression was used to determine independent risk factors for slides with interpersonal discordant diagnosis. The variables studied were BCC presence, whether a slide was scored as easy or difficult to diagnose, review duration of the 50 slides, profession and years of experience in diagnosis from Mohs slides.

RESULTS

Interpersonal and intrapersonal agreement were substantial on BCC presence (κ = 0·66 and 0·68) and moderate on BCC subtype (κ = 0·45 and 0·55). Slides that were scored as difficult to diagnose were an independent risk factor for interpersonal discordant diagnosis on BCC presence (odds ratio 3·54, 95% confidence interval 1·81-6·84).

CONCLUSIONS

Reliability of diagnosis from Mohs slides was substantial on BCC presence and moderate on BCC subtype. For slides that are scored difficult to diagnose, a second opinion is recommended to prevent misinterpretation and thereby recurrence of skin cancer.

On the horizon: Optical imaging for cutaneous squamous cell carcinoma

BACKGROUND

Surgical resection with negative margins remains the standard of care for high-risk cutaneous squamous cell carcinoma (SCC). However, surgical management is often limited by poor intraoperative tumor visualization and inability to detect occult nodal metastasis. The inability to intraoperatively detect microscopic disease can lead to additional surgery, tumor recurrence, and decreased survival.

METHODS

A comprehensive literature review was conducted to identify studies incorporating optical imaging technology in the management of cutaneous SCC (January 1, 2000-December 1, 2014).

RESULTS

Several innovative optical imaging techniques, Raman spectroscopy, confocal microscopy, and fluorescence imaging, have been developed for intraoperative surgical guidance. Fifty-seven studies review the ability of these techniques to improve cutaneous SCC localization at the gross and microscopic level.

CONCLUSION

Significant advances have been achieved with real-time optical imaging strategies for intraoperative cutaneous SCC margin assessment and tumor detection. Optical imaging holds promise in improving the percentage of negative surgical margins and in the early detection of micrometastatic disease. © 2015 Wiley Periodicals, Inc. Head Neck 38: E2204-E2213, 2016.

Additional review of Mohs slides to optimize Mohs micrographic surgery

BACKGROUND

One significant risk factor for recurrence after Mohs surgery is misinterpretation of slides.

OBJECTIVES

To determine how often pathologists detected incompletely excised basal cell carcinoma (BCC) on Mohs slides and to determine risk factors for incompletely excised BCCs.

METHODS

This retrospective study included 1653 BCCs treated with Mohs surgery in a university hospital between 2007 and 2011. For routine quality assurance, all slides were additionally reviewed by a pathologist within 1 week of the procedure. For this study, all cases that had divergent interpretations were re-evaluated by a Mohs surgeon and a pathologist. Mixed-effects logistic regression models with Mohs surgeon effects as random effects were used to determine risk factors for incompletely excised BCC.

RESULTS

Incompletely excised BCCs were detected in 31 cases (2%), in which defects > 20 mm in diameter were an independent risk factor (odds ratio 3.58, 95% confidence interval 1.55-8.28). Other studied variables (i.e. aggressive subtype, previously treated BCC, location on nose and > 2 Mohs stages) did not affect the risk of incompletely excised BCCs.

CONCLUSIONS

The additional review of Mohs slides might increase accurate interpretation, especially in large BCCs.

Management of squamous cell and basal cell carcinomas of the head and neck with perineural invasion

Perineural invasion (PNI) occurring in non-melanoma skin cancers (NMSC) is associated with an increased risk of locoregional recurrence and reduced disease-free survival. This necessitates early and accurate diagnosis, appropriate risk-stratification and a clear management strategy. The diagnosis of PNI is based on careful clinical assessment, imaging and histopathology. Surgery, preferably with margin control, and definitive or adjuvant radiotherapy (ART) are established treatment strategies for PNI. Clinical uncertainty remains over the role of ART in incidental PNI. This review synthesises current literature to ascertain which clinicopathological features impart a higher risk to individuals with PNI in NMSC, in order to provide treatment algorithms, including the identification of patient subsets that are most likely to benefit from ART. This includes those with extratumoural PNI, involvement of larger-calibre nerves, tumour invasion beyond dermis, recurrent tumour or diffuse intratumoural spread. Patients with clinical PNI may be optimally managed by a multidisciplinary head and neck cancer service that is best placed to offer skull base surgery and intensity-modulated radiation therapy (IMRT). The management options presented are stratified by histological subtype and a new classification of PNI into low-risk, medium-risk and high-risk groups.