Position paper on a simplified histopathological classification of basal cell carcinoma: results of the European Consensus Project

Frequent Occurrence of High-Risk Basal Cell Carcinoma in Xeroderma Pigmentosum: A Histopathological Insight From an Indian Cohort

BACKGROUND

Xeroderma pigmentosum (XP) is a genodermatosis, characterized both by premature aging and significantly increased risk of non-melanoma and melanoma skin cancers at an early age. However, limited literature is available on the common histopathological subtypes of basal cell carcinoma (BCC) in these patients.

METHODS

In this ambispective case series, we recruited patients of XP who had either a currently present skin tumor or previously excised one, provided their histopathological sections were available. Cytogenetic analysis was performed in all the patients. The histopathological findings were recorded by two trained dermatopathologists.

RESULTS

Of 22 recruited patients with XP, 12 patients had 41 BCCs, and 23 (56.09%) of them showed a high-risk histopathological subtype. Basosquamous carcinoma (10, 24.39%) was the most frequent high-risk tumor followed by infiltrative variant (7, 17.07%). Mixed-histopathological subtypes were noted in six (14.63%) cases, and all of them had a high-risk component. The low-risk subtypes included nodular (n = 17, 41.46%) and superficial BCC (1, 2.43%). Though a deep dermal involvement was seen in 27 (65.85%) lesions, none showed a perineural invasion or necrosis. Three (7.31%) lesions showed ulceration, while 10 (24.39%) showed presence of pigmentation.

CONCLUSIONS

A frequent occurrence of high-risk basal cell carcinoma was noted in patients with XP-mandating creation of appropriate treatment and follow-up strategies in these patients.

Re-evaluation of the concept of basaloid follicular hamartoma associated with naevoid basal cell carcinoma syndrome: a morphological, immunohistochemical and molecular study

Naevoid basal cell carcinoma syndrome (NBCCS) is a rare genodermatosis caused by germline mutations in genes of the Sonic Hedgehog (SHH) pathway and is characterised by early onset of multiple basal cell carcinomas (BCCs). Although skin tumours with follicular differentiation, notably basaloid follicular hamartoma (BFH), have been reported in NBCCS, their relations with BCC are poorly defined. In this context, the aim of this study was to clarify morphological, immunohistochemical ​and molecular features of BFH arising in a context of NBCCS. A total of 140 skin tumours from NBCCS and 140 control BCC tumours were reviewed, blinded to clinical data and classified as BCC or BFH. The morphological characteristics of these two groups were then compared. Twenty cases were submitted for immunohistochemical and molecular analysis. Thirty-three tumours among the exploratory cohort were classified as BFH and were exclusively detected in NBCCS patients. Histopathological criteria that were significantly different from BCC were as follows: a small size (<1.5 mm), connection to a hair follicle, arborescent organoid architecture, lack of cytological atypia and infundibulocystic differentiation. Immunohistochemical analysis confirmed activation of the SHH pathway in these lesions. Targeted next-generation sequencing suggested that MYCN and GLI2/3 amplifications and TP53 mutations might be involved in progression of these follicular tumours to BCC. Our study confirms the high prevalence of BFH, representing up to 24% of skin tumours in NBCCS and potentially being BCC precursors.

Cancer-associated fibroblast subtypes modulate the tumor-immune microenvironment and are associated with skin cancer malignancy

Cancer-associated fibroblasts (CAFs) play a key role in cancer progression and treatment outcome. This study dissects the intra-tumoral diversity of CAFs in basal cell carcinoma, squamous cell carcinoma, and melanoma using molecular and spatial single-cell analysis. We identify three distinct CAF subtypes: myofibroblast-like RGS5+ CAFs, matrix CAFs (mCAFs), and immunomodulatory CAFs (iCAFs). Large-cohort tissue analysis reveals significant shifts in CAF subtype patterns with increasing malignancy. Two CAF subtypes exhibit immunomodulatory properties via different mechanisms. mCAFs sythesize extracellular matrix and may restrict T cell invasion in low-grade tumors via ensheathing tumor nests, while iCAFs are enriched in late-stage tumors, and express high levels of cytokines and chemokines to aid immune cell recruitment and activation. This is supported by the induction of an iCAF-like phenotype with immunomodulatory functions in primary healthy fibroblasts exposed to skin cancer cell secretomes. Thus, targeting CAF variants holds promise to enhance immunotherapy efficacy in skin cancers.

The 2023 WHO updates on skin tumors: advances since the 2018 edition

Pathology is pivotal in diagnosing skin tumors, and the precision of diagnosis is crucial to devise customized treatment plans and enhance patient care in dermatology. The latest edition of the World Health Organization's classification of skin tumors serves as a comprehensive compendium, summarizing and categorizing all recent advancements in both anatomical-pathological and molecular aspects of cutaneous neoplasms. Several relevant advances have been introduced and new entities have been described. While the fundamental structure of the classification remains unchanged, notable additions include three new sections aimed at providing a more exhaustive description of skin lesions: nail unit tumors, skin metastases, and genetic tumor syndromes associated with skin malignancies. Recent strides in molecular pathology have led to significant breakthroughs in decoding the underlying mechanisms of various skin tumors, ranging from adnexal neoplasms to hematolymphoid neoplasms, soft tissue tumors, and melanocytic lesions. Of particular importance is the evolution in our understanding of melanocytic neoplasms, with the introduction of the term "melanocytoma" reserved for lesions exhibiting "intermediate" biological behavior and characterized by specific molecular mutations. The pathologic diagnosis process integrates morphological, immunohistochemical, and molecular features, playing a crucial role in clinical decision-making. The WHO classification serves as a valuable tool in promoting multidisciplinarity in the management of cutaneous neoplasms with the aim of translating novel pathological discoveries into more effective treatments. This review aims to distill the major updates introduced by the new classification, providing a synthesis of the latest scientific insights.

Predictors of Local Invasion in Infiltrative Basal Cell Carcinoma: Tumour Budding Outperforms the WHO Subtyping

Tumour budding (TB) correlates with increased local invasion in various neoplasms. Certain basal cell carcinomas (BCCs) exhibit local aggressiveness. Detecting adverse prognostic factors in partial biopsies could aid in identifying cases with heightened local risk. The absolute number of TB (≤ 3 tumour cells) in excision specimens of 271 infiltrative BCCs (0: absent; 1: 1-2 foci; 2: ≥ 3 foci; 3: ≥ 10 foci), the histopathological subtype and depth of infiltration, perineural invasion, and other histological features were evaluated. A significant correlation was found between TB and both depth of infiltration (rho 0.445, p < 0.001) and perineural invasion (p = 0.009). In the multivariate analysis of depth and perineural invasion (multiple regression, stepwise), TB was identified as a significant covariate together with diameter, inflammation, and perineural invasion for the former, and depth for the latter. Conversely, no correlation existed between the WHO histological subtypes (infiltrating, sclerosing, and micronodular), and depth of infiltration or perineural invasion. This study demonstrates the value of TB as a biomarker for local invasiveness in BCC. In routine practice, a count of ≥ 3 TB foci in lesions incompletely excised or with narrow tumour-free surgical margins would be a straightforward and reproducible method to guide BCC treatment.

Detection and subtyping of basal cell carcinoma in whole-slide histopathology using weakly-supervised learning

The frequency of basal cell carcinoma (BCC) cases is putting an increasing strain on dermatopathologists. BCC is the most common type of skin cancer, and its incidence is increasing rapidly worldwide. AI can play a significant role in reducing the time and effort required for BCC diagnostics and thus improve the overall efficiency of the process. To train such an AI system in a fully-supervised fashion however, would require a large amount of pixel-level annotation by already strained dermatopathologists. Therefore, in this study, our primary objective was to develop a weakly-supervised for the identification of basal cell carcinoma (BCC) and the stratification of BCC into low-risk and high-risk categories within histopathology whole-slide images (WSI). We compared Clustering-constrained Attention Multiple instance learning (CLAM) with StreamingCLAM and hypothesized that the latter would be the superior approach. A total of 5147 images were used to train and validate the models, which were subsequently tested on an internal set of 949 images and an external set of 183 images. The labels for training were automatically extracted from free-text pathology reports using a rule-based approach. All data has been made available through the COBRA dataset. The results showed that both the CLAM and StreamingCLAM models achieved high performance for the detection of BCC, with an area under the ROC curve (AUC) of 0.994 and 0.997, respectively, on the internal test set and 0.983 and 0.993 on the external dataset. Furthermore, the models performed well on risk stratification, with AUC values of 0.912 and 0.931, respectively, on the internal set, and 0.851 and 0.883 on the external set. In every single metric the StreamingCLAM model outperformed the CLAM model or is on par. The performance of both models was comparable to that of two pathologists who scored 240 BCC positive slides. Additionally, in the public test set, StreamingCLAM demonstrated a comparable AUC of 0.958, markedly superior to CLAM's 0.803. This difference was statistically significant and emphasized the strength and better adaptability of the StreamingCLAM approach.

Differentiation and risk stratification of basal cell carcinoma with deep learning on histopathologic images and measuring nuclei and tumor microenvironment features

BACKGROUND

Nuclear pleomorphism and tumor microenvironment (TME) play a critical role in cancer development and progression. Identifying most predictive nuclei and TME features of basal cell carcinoma (BCC) may provide insights into which characteristics pathologists can use to distinguish and stratify this entity.

OBJECTIVES

To develop an automated workflow based on nuclei and TME features from basaloid cell tumor regions to differentiate BCC from trichoepithelioma (TE) and stratify BCC into high-risk (HR) and low-risk (LR) subtypes, and to identify the nuclear and TME characteristics profile of different basaloid cell tumors.

METHODS

The deep learning systems were trained on 161 H&E -stained sections which contained 51 sections of HR-BCC, 50 sections of LR-BCC and 60 sections of TE from one institution (D1), and externally and independently validated on D2 (46 sections) and D3 (76 sections), from 2015 to 2022. 60%, 20% and 20% of D1 data were randomly splitted for training, validation and testing, respectively. The framework comprised four stages: tumor regions identification by multi-head self-attention (MSA) U-Net, nuclei segmentation by HoVer-Net, quantitative feature by handcrafted extraction, and differentiation and risk stratification classifier construction. Pixel accuracy, precision, recall, dice score, intersection over union (IoU) and area under the curve (AUC) were used to evaluate the performance of tumor segmentation model and classifiers.

RESULTS

MSA-U-Net model detected tumor regions with 0.910 precision, 0.869 recall, 0.889 dice score and 0.800 IoU. The differentiation classifier achieved 0.977 ± 0.0159, 0.955 ± 0.0181, 0.885 ± 0.0237 AUC in D1, D2 and D3, respectively. The most discriminative features between BCC and TE contained Homogeneity, Elongation, T-T_meanEdgeLength, T-T_Nsubgraph, S-T_HarmonicCentrality, S-S_Degrees. The risk stratification model can well predict HR-BCC and LR-BCC with 0.920 ± 0.0579, 0.839 ± 0.0176, 0.825 ± 0.0153 AUC in D1, D2 and D3, respectively. The most discriminative features between HR-BCC and LR-BCC comprised IntensityMin, Solidity, T-T_minEdgeLength, T-T_Coreness, T-T_Degrees, T-T_Betweenness, S-T_Degrees.

CONCLUSIONS

This framework hold potential for future use as a second opinion helping inform diagnosis of BCC, and identify nuclei and TME features related with malignancy and tumor risk stratification.

Inter-rater concordance of basal cell carcinoma subtypes: influences on reporting format and opportunities for further classification modifications

Diagnosis of basal cell carcinoma (BCC) higher risk subtypes influences management strategies because of their propensity to recur locally. Subtyping is prone to inter-observer variability, and subtyping definitions are inconsistently applied. This study sought to compare the interobserver reproducibility of individual BCC subtypes using the 4th edition World Health Organization (WHO) Classification of Skin Tumours (CoST) definitions, with classification into lower and higher risk histological subtype groups. Ninety-one BCC cases were rated by seven pathologists, noting the presence of BCC subtype(s), and providing a higher or lower risk subtype grouping per case. Raters were provided with definitions as per the 4th edition WHO CoST for 10 listed BCC subtypes. Surgical specimen type was noted. Subgroup analysis was performed to exclude cases when the tumour deep front was not well visualised, or there was tangential sectioning (n = 6). Light's kappa was used to assess inter-rater reliability. From the total group (n = 91), five BCC subtypes showed a sufficient number of ratings for computing a κ statistic. From these five subtypes, superficial subtype showed substantial inter-rater agreement (κ = 0.64), and the other four subtypes showed moderate inter-rater agreement [nodular (κ = 0.45), sclerosing/morphoeic (κ = 0.45), infiltrating (κ = 0.49) and micronodular (κ = 0.57)]. Two-tiered rating into either higher or lower risk subtype showed substantial inter-rater agreement (κ = 0.72). Our results suggest a need to more precisely define BCC subtypes. We suggest reporting BCC subtype using a two-tiered risk grouping, followed by specific subtypes present. Further studies examining the inter-rater reliability of less common BCC subtypes are required.

European consensus-based interdisciplinary guideline for diagnosis and treatment of basal cell carcinoma-update 2023

Basal cell carcinoma (BCC) is the most common malignant tumour in white populations. Multidisciplinary experts from European Association of Dermato-Oncology (EADO), European Dermatology Forum, European Society for Radiotherapy and Oncology (ESTRO), Union Européenne des Médecins Spécialistes, and the European Academy of Dermatology and Venereology developed updated recommendations on diagnosis and treatment of BCC. BCCs were categorised into 'easy-to-treat' (common) and 'difficult-to-treat' according to the new EADO clinical classification. Diagnosis is based on clinico-dermatoscopic features, although histopathological confirmation is mandatory in equivocal lesions. The first-line treatment of BCC is complete surgery. Micrographically controlled surgery shall be offered in high-risk and recurrent BCC, and BCC located on critical anatomical sites. Topical therapies and destructive approaches can be considered in patients with low-risk superficial BCC. Photodynamic therapy is an effective treatment for superficial and low-risk nodular BCCs. Management of 'difficult-to-treat' BCCs should be discussed by a multidisciplinary tumour board. Hedgehog inhibitors (HHIs), vismodegib or sonidegib, should be offered to patients with locally advanced and metastatic BCC. Immunotherapy with anti-PD1 antibodies (cemiplimab) is a second-line treatment in patients with a progression of disease, contraindication, or intolerance to HHI therapy. Radiotherapy represents a valid alternative in patients who are not candidates for or decline surgery, especially elderly patients. Electrochemotherapy may be offered when surgery or radiotherapy is contraindicated. In Gorlin patients, regular skin examinations are required to diagnose and treat BCCs at an early stage. Long-term follow-up is recommended in patients with high-risk BCC, multiple BCCs, and Gorlin syndrome.

Sarcomatoid transformation of a basal cell carcinoma following treatment with hedgehog inhibitors

Vismodegib and sonidegib are sonic hedgehog inhibitors (SHHIs) available for the treatment of advanced basal cell carcinoma (BCC). Cases of sarcomatoid differentiation during treatment of BCC with SHHIs have not been previously reported. We present a unique case of a locally advanced BCC that underwent sarcomatoid transformation, manifesting as a large mass complicated by local invasion and lung metastases, following treatment with sonidegib.

Acantholytic Nodular Basal Cell Carcinoma

ABSTRACT

Acantholysis is a microscopic finding describing the breakdown of desmosomes of keratinocytes and the formation of intraepithelial clefts after the loss of cohesion of keratinocytes. It can be observed in keratinocytic neoplasms, typically actinic keratoses and squamous cell carcinomas, and defines the acantholytic variants of these entities. Acantholysis has so far been reported in only 4 cases of basal cell carcinomas (BCCs), mainly of the superficial type. A case of an otherwise typical nodular BCC showing features of acantholysis is presented here. Because BCCs are keratinocytic neoplasms, the finding of acantholysis in them is not totally surprising; however, the reason why it is only very exceptionally observed in BCCs is unclear.

Myofibroblast stroma differentiation in infiltrative basal cell carcinoma is accompanied by regulatory T-cells

INTRODUCTION

The implications of infiltrative compared to non-infiltrative growth of cutaneous basal cell carcinoma (BCC) on the tumor stroma and immune cell landscape are unknown. This is of clinical importance, because infiltrative BCCs, in contrast to other BCC subtypes, are more likely to relapse after surgery and radiotherapy.

MATERIALS AND METHODS

This descriptive cross-sectional study analyzed 38 BCCs collected from 2018 to 2021. In the first cohort (n = 28), immune cells were characterized by immunohistochemistry and multiplex immunofluorescence staining for CD3, CD8, CD68, Foxp3, and α-SMA protein expression. In the second cohort (n = 10) with matched characteristics (age, sex, location, and BCC subtype), inflammatory parameters, including TGF-β1, TGF-β2, ACTA2, IL-10, IL-12A, and Foxp3, were quantified via RT-qPCR after isolating mRNA from BCC tissue samples and perilesional skin.

RESULTS

Infiltrative BCCs showed significantly increased levels of α-SMA expression in fibroblasts (p = 0.0001) and higher levels of Foxp3+ (p = 0.0023) and CD3+ (p = 0.0443) T-cells compared to non-infiltrative BCCs. CD3+ (p = 0.0171) and regulatory T-cells (p = 0.0026) were significantly increased in α-SMA-positive tumor stroma, whereas CD8+ T-cells (p = 0.1329) and CD68+ myeloid cells (p = 0.2337) were not affected. TGF-β1 and TGF-β2 correlated significantly with ACTA2/α-SMA mRNA expression (p = 0.020, p = 0.005).

CONCLUSION

Infiltrative growth of BCCs shows a myofibroblastic stroma differentiation and is accompanied by an immunosuppressive tumor microenvironment.

Accuracy of Optical Coherence Tomography for Subtyping Basal Cell Carcinoma: Using Histopathology of Biopsy and Entire Lesion as Reference Standard

Abstract is missing (Short communication)

Basal cell carcinoma: Epidemiological impact of clinical versus histopathological diagnosis

BACKGROUND

Low-risk basal cell carcinomas (BCCs) are to an increasing extent diagnosed by dermatologists through dermoscopic examination only and treated with non-surgical methods. Reports on increasing incidence as well as trends regarding subtypes, anatomical sites and differences related to gender are based solely on histopathologically verified tumours. How unreported clinically diagnosed BCCs affect the epidemiological data has not been sufficiently investigated.

OBJECTIVES

To analyse the tumour and patient characteristics of clinically diagnosed versus histopathologically confirmed primary BCCs and to make a gross estimate on how unreported BCCs could influence the total number of new cases.

METHODS

We retrospectively reviewed all primary BCCs diagnosed in 2016 at the Department of Dermatology, Sahlgrenska University Hospital in Gothenburg, Sweden. We also reviewed all histopathologically verified primary BCCs at the two largest pathology laboratories in Western Sweden during the same year to estimate the proportion of BCCs diagnosed by dermatologists.

RESULTS

In total, 2365 primary BCCs were diagnosed at our centre. More than half of these tumours were clinically diagnosed (55.8%). Superficial subtype (41.7%), location on the trunk (46.3%) and destructive treatment methods (60.0%) were most common. The reports from the two pathology laboratories showed that histopathologically verified BCCs (n = 5837) were more commonly of the infiltrative or nodular subtype and located in the head and neck area. Dermatologists managed 56.0% of them.

CONCLUSIONS

This study indicates that a substantial number of BCCs are not visualized in the official statistics which are solely based on reports from pathology laboratories. When taking clinically diagnosed tumours into account, truncal location and superficial subtype are more common than previously believed. Further, based on the regional calculations, the real burden of BCC in Sweden might be up to 70% higher than what is reported in official statistics.

Management of patients with giant basal cell carcinoma during SARS COV2 outbreak in Italy

Basal cell carcinoma (BCC) is the most frequently occurring type of all cancers, and represents 80% of all skin cancer. The estimated lifetime risk for BCC in the white population is between 33% and 39% for men and 23% and 28% for women. Its incidence doubles every 25 years and is increasing in the young population. Death is uncommon and seems to decrease in the last years, probably due to early and better diagnosis. BCC arises from abnormal and uncontrolled growth of basal cells. It is a slow-growing tumor, therefore usually curable at an early stage with surgery or alternative treatment, such as cryotherapy, laser, photodynamic therapy, retinoids and topical agent like 5-Fluorouracil cream, imiquimod cream, and so forth. Topical treatment of superficial basocellular carcinoma is a viable option, when surgery is not an advisable treatment, especially in the case of giant basocellular carcinoma. In this subtype, imiquimod 5% cream can be a safe and effective treatment, but there are few reports in available literature. We present our case series of eight patients with superficial giant basocellular carcinoma successfully treated with imiquimod 5% cream, which showed clinical improvement after 8 weeks of treatment.