Identification of the cell lineage at the origin of basal cell carcinoma

A developmental constraint model of cancer cell states and tumor heterogeneity

Cancer is a disease that stems from a fundamental liability inherent to multicellular life forms in which an individual cell is capable of reneging on the interests of the collective organism. Although cancer is commonly described as an evolutionary process, a less appreciated aspect of tumorigenesis may be the constraints imposed by the organism's developmental programs. Recent work from single-cell transcriptomic analyses across a range of cancer types has revealed the recurrence, plasticity, and co-option of distinct cellular states among cancer cell populations. Here, we note that across diverse cancer types, the observed cell states are proximate within the developmental hierarchy of the cell of origin. We thus posit a model by which cancer cell states are directly constrained by the organism's "developmental map." According to this model, a population of cancer cells traverses the developmental map, thereby generating a heterogeneous set of states whose interactions underpin emergent tumor behavior.

TRPS1 expression in non-melanocytic cutaneous neoplasms: an immunohistochemical analysis of 200 cases

BACKGROUND

Although trichorhinophalangeal syndrome type 1 (TRPS1) was initially thought to be highly sensitive and specific for carcinomas and mesenchymal tumors of mammary origin, more recent data suggest its expression is not limited to breast neoplasms but also can be seen in other cutaneous neoplasms, such as extramammary Paget disease and squamous cell carcinoma (SCC) in situ.

METHODS

Two-hundred cases of non-melanocytic cutaneous neoplasm, including basal cell carcinomas (BCCs) (n = 41), SCCs (n = 35), Merkel cell carcinomas (MCCs) (n = 25), and adnexal neoplasms (n = 99), were tested for TRPS1 expression using a monoclonal anti- TRPS1 rabbit anti-human antibody.

RESULTS

TRPS1 expression was present in almost all cases of SCC (94%), with a median H-score of 200, while it was either absent or only focally present in most BCCs (90%), with a median H-score of 5. The difference between BCCs and SCCs in H-score was significant (p < .001). All MCCs (100%) lacked TRPS1 expression. TRPS1 expression was frequently seen in most adnexal neoplasms, benign and malignant, in variable intensity and proportion but was consistently absent in apocrine carcinomas. All endocrine mucin-producing sweat gland carcinomas (EMPSGCs) (100%, 6/6) showed diffuse and strong TRPS1 immunoreactivity, with a median H-score of 300, which was significantly different (p < .001) than that of BCCs.

CONCLUSIONS

Our study shows that TRPS1 may be an effective discriminatory marker for BCCs and SCCs. It also has a role in distinguishing BCCs from EMPSGCs.

Can the Safe Surgical Margin Be Narrowed in Early-Stage Facial Basal Cell Carcinoma?

OBJECTIVE

To examine factors that affect the positive surgical margins of facial basal cell carcinoma (BCC) and investigate whether the surgical margin value can be narrowed in early-stage facial BCCs.

METHODS

Ninety-five patients were divided into the three groups based on prognosis: good (n = 48), mixed (n = 32), and poor (n = 15). The good prognosis group (group 1) included nodular and superficial subtypes; the mixed prognosis group (group 2) included nodular-infiltrative, nodular-micronodular, and nodular-sclerosing subtypes; and the poor prognosis group (group 3) included infiltrative and micronodular subtypes.

RESULTS

Groups 1 and 2 differed from each other significantly in terms of positive surgical margin (P = .002) and tumor thickness (P = .008), but group 3 did not (P = .851 and P = .804, respectively). With regard to surgical method (primary vs local flap repair), only tumor localization varied significantly (P < .001).

CONCLUSIONS

Groups differed significantly in terms of surgical margin positivity, the distance of the tumor to the surgical margin, and the tumor thickness. The intact surgical margin was 2 mm on average in this study, and the authors suggest that it may be possible to revise the surgical margin values recommended in the literature.

Multiscale spatial mapping of cell populations across anatomical sites in healthy human skin and basal cell carcinoma

Our understanding of how human skin cells differ according to anatomical site and tumour formation is limited. To address this, we have created a multiscale spatial atlas of healthy skin and basal cell carcinoma (BCC), incorporating in vivo optical coherence tomography, single-cell RNA sequencing, spatial global transcriptional profiling, and in situ sequencing. Computational spatial deconvolution and projection revealed the localisation of distinct cell populations to specific tissue contexts. Although cell populations were conserved between healthy anatomical sites and in BCC, mesenchymal cell populations including fibroblasts and pericytes retained signatures of developmental origin. Spatial profiling and in silico lineage tracing support a hair follicle origin for BCC and demonstrate that cancer-associated fibroblasts are an expansion of a POSTN+ subpopulation associated with hair follicles in healthy skin. RGS5+ pericytes are also expanded in BCC suggesting a role in vascular remodelling. We propose that the identity of mesenchymal cell populations is regulated by signals emanating from adjacent structures and that these signals are repurposed to promote the expansion of skin cancer stroma. The resource we have created is publicly available in an interactive format for the research community.

Oncofetal reprogramming in tumor development and progression: novel insights into cancer therapy

Emerging evidence indicates that cancer cells can mimic characteristics of embryonic development, promoting their development and progression. Cancer cells share features with embryonic development, characterized by robust proliferation and differentiation regulated by signaling pathways such as Wnt, Notch, hedgehog, and Hippo signaling. In certain phase, these cells also mimic embryonic diapause and fertilized egg implantation to evade treatments or immune elimination and promote metastasis. Additionally, the upregulation of ATP-binding cassette (ABC) transporters, including multidrug resistance protein 1 (MDR1), multidrug resistance-associated protein 1 (MRP1), and breast cancer-resistant protein (BCRP), in drug-resistant cancer cells, analogous to their role in placental development, may facilitate chemotherapy efflux, further resulting in treatment resistance. In this review, we concentrate on the underlying mechanisms that contribute to tumor development and progression from the perspective of embryonic development, encompassing the dysregulation of developmental signaling pathways, the emergence of dormant cancer cells, immune microenvironment remodeling, and the hyperactivation of ABC transporters. Furthermore, we synthesize and emphasize the connections between cancer hallmarks and embryonic development, offering novel insights for the development of innovative cancer treatment strategies.

Cancer-associated immune cells and their modulation by melatonin

OBJECTIVES

Rapidly growing evidence suggests that immune cells play a key role in determining tumor progression. Tumor cells are surrounded by a microenvironment composed of different cell populations including immune cells. The cross talk between tumor cells and the neighboring microenvironment is an important factor to take into account while designing tumor therapies. Despite significant advances in immunotherapy strategies, a relatively small proportion of patients have successfully responded to them. Therefore, the search for safe and efficient drugs, which could be used alongside conventional therapies to boost the immune system against tumors, is an ongoing need. In the present work, the modulatory effects of melatonin on different components of tumor immune microenvironment are reviewed.

METHODS

A thorough literature review was performed in PubMed, Scopus, and Web of Science databases. All published papers in English on tumor immune microenvironment and the relevant modulatory effects of melatonin were scrutinized.

RESULTS

Melatonin modulates macrophage polarization and prevents M2 induction. Moreover, it prevents the conversion of fibroblasts into cancer-associated fibroblasts (CAFs) and prevents cancer cell stemness. In addition, it can affect the payload composition of tumor-derived exosomes (TEXs) and their secretion levels to favor a more effective anti-tumor immune response. Melatonin is a safe molecule that affects almost all components of the tumor immune microenvironment and prevents them from being negatively affected by the tumor.

CONCLUSION

Based on the effects of melatonin on normal cells, tumor cells and microenvironment components, it could be an efficient compound to be used in combination with conventional immune-targeted therapies to increase their efficacy.

Feline papillomavirus-associated Merkel cell carcinoma: a comparative review with human Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare skin tumor that shares a similar immunophenotype with Merkel cells, although its origin is debatable. More than 80% of human MCC cases are associated with Merkel cell polyomavirus infections and viral gene integration. Recent studies have shown that the clinical and pathological characteristics of feline MCC are comparable to those of human MCC, including its occurrence in aged individuals, aggressive behavior, histopathological findings, and the expression of Merkel cell markers. More than 90% of feline MCC are positive for the Felis catus papillomavirus type 2 (FcaPV2) gene. Molecular changes involved in papillomavirus-associated tumorigenesis, such as increased p16 and decreased retinoblastoma (Rb) and p53 protein levels, were observed in FcaPV2-positive MCC, but not in FcaPV2-negative MCC cases. These features were also confirmed in FcaPV2-positive and -negative MCC cell lines. The expression of papillomavirus E6 and E7 genes, responsible for p53 degradation and Rb inhibition, respectively, was detected in tumor cells by in situ hybridization. Whole genome sequencing revealed the integration of FcaPV2 DNA into the host feline genome. MCC cases often develop concurrent skin lesions, such as viral plaque and squamous cell carcinoma, which are also associated with papillomavirus infection. These findings suggest that FcaPV2 infection and integration of viral genes are involved in the development of MCC in cats. This review provides an overview of the comparative pathology of feline and human MCC caused by different viruses and discusses their cell of origin.

Exploring multisite heterogeneity of human basal cell carcinoma proteome and transcriptome

Basal cell carcinoma (BCC) is the most common type of skin cancer. Due to multiple, potential underlying molecular tumor aberrations, clinical treatment protocols are not well-defined. This study presents multisite molecular heterogeneity profiles of human BCC based on RNA and proteome profiling. Three areas from lesions excised from 9 patients were analyzed. The focus was gene expression profiles based on proteome and RNA measurements of intra-tumor heterogeneity from the same patient and inter-tumor heterogeneity in nodular, infiltrative, and superficial BCC tumor subtypes from different patients. We observed significant overlap in intra- and inter-tumor variability of proteome and RNA expression profiles, showing significant multisite heterogeneity of protein expression in the BCC tumors. Inter-subtype analysis has also identified unique proteins for each BCC subtype. This profiling leads to a deeper understanding of BCC molecular heterogeneity and potentially contributes to developing new sampling tools for personalized diagnostics therapeutic approaches to BCC.

The extracellular matrix dictates regional competence for tumour initiation

The skin epidermis is constantly renewed throughout life1,2. Disruption of the balance between renewal and differentiation can lead to uncontrolled growth and tumour initiation3. However, the ways in which oncogenic mutations affect the balance between renewal and differentiation and lead to clonal expansion, cell competition, tissue colonization and tumour development are unknown. Here, through multidisciplinary approaches that combine in vivo clonal analysis using intravital microscopy, single-cell analysis and functional analysis, we show how SmoM2-a constitutively active oncogenic mutant version of Smoothened (SMO) that induces the development of basal cell carcinoma-affects clonal competition and tumour initiation in real time. We found that expressing SmoM2 in the ear epidermis of mice induced clonal expansion together with tumour initiation and invasion. By contrast, expressing SmoM2 in the back-skin epidermis led to a clonal expansion that induced lateral cell competition without dermal invasion and tumour formation. Single-cell analysis showed that oncogene expression was associated with a cellular reprogramming of adult interfollicular cells into an embryonic hair follicle progenitor (EHFP) state in the ear but not in the back skin. Comparisons between the ear and the back skin revealed that the dermis has a very different composition in these two skin types, with increased stiffness and a denser collagen I network in the back skin. Decreasing the expression of collagen I in the back skin through treatment with collagenase, chronic UV exposure or natural ageing overcame the natural resistance of back-skin basal cells to undergoing EHFP reprogramming and tumour initiation after SmoM2 expression. Altogether, our study shows that the composition of the extracellular matrix regulates how susceptible different regions of the body are to tumour initiation and invasion.

Signaling Pathways and Therapeutic Strategies in Advanced Basal Cell Carcinoma

Non-melanoma skin cancers (NMSCs) are the most common human neoplasms world-wide. In detail, basal cell carcinoma (BCC) is the most frequent malignancy in the fair-skinned population. The incidence of BCC remains difficult to assess due to the poor registration practice; however, it has been increasing in the last few years. Approximately, 85% of sporadic BCCs carry mutations in Hedgehog pathway genes, especially in PTCH, SUFU and SMO genes, which lead to the aberrant activation of GLI transcriptional factors, typically silent in cells of adult individuals. The management of advanced BCC (aBCC), both metastatic (mBCC) and locally advanced BCC (laBCC), not candidates for surgical excision or radiotherapy, remains challenging. The discovery of mutations in the Hh signaling pathway has paved the way for the development of Hh pathway inhibiting agents, such as vismodegib and sonidegib, which have represented a breakthrough in the aBCC management. However, the use of these agents is limited by the frequent occurrence of adverse events or the development of drug resistance. In this review, we thoroughly describe the current knowledge regarding the available options for the pharmacological management of aBCCs and provide a forward-looking update on novel therapeutic strategies that could enrich the therapeutic armamentarium of BCC in the near future.

Topical 188Re Ionizing Radiation Therapy Exerts High Efficacy in Curing Nonmelanoma Skin Cancer

PURPOSE OF THE REPORT

Nonmelanoma skin cancer (NMSC) is the most frequent malignancy. Surgical intervention is the common treatment but may lead to disappointing results; alternative treatment options are needed.

METHODS

In this monocentric pilot study, topical 188Re resin was investigated as a treatment for invasive NMSC up to 3-mm thickness. Twenty-two patients with 40 histologically confirmed NMSCs with a median size of 1.25 cm2 (range, 0.04-16.8 cm2) and a median tumor thickness of 0.35 mm (range, 0.1-2.1 mm) were included. Patients were treated once with 188Re resin with a targeted dose of 50 Gy. The median applied activity was 111.4 MBq (range, 21.0-168.0 MBq), and the median treatment time was 89 minutes (range, 38-175 minutes). The response rate, adverse events, and cosmetic outcome were assessed at 14 days, 4 months, and 12 months.

RESULTS

Response rate at 12 months was 97.5%, with 95% complete responses (clinically or histologically proven in case of clinical doubt). Most adverse events were reported at 14 days, with 20% itching and 12.5% mostly minor pain. Forty-nine percent of the lesions showed hypopigmentation only at 12 months. Forty-one percent of the lesions were graded as cosmetically superior to the expected result after surgery and 51.3% as comparable to successful surgery. The cosmetic outcome on the head and face was superior compared with the trunk and leg (P = 0.003).

CONCLUSION

188Re resin is a highly effective treatment for NMSC up to 3-mm thickness and a valid alternative to surgery, specifically for tumors located on sensitive areas such as nose or ear.

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.

The pioneer factor SOX9 competes for epigenetic factors to switch stem cell fates

During development, progenitors simultaneously activate one lineage while silencing another, a feature highly regulated in adult stem cells but derailed in cancers. Equipped to bind cognate motifs in closed chromatin, pioneer factors operate at these crossroads, but how they perform fate switching remains elusive. Here we tackle this question with SOX9, a master regulator that diverts embryonic epidermal stem cells (EpdSCs) into becoming hair follicle stem cells. By engineering mice to re-activate SOX9 in adult EpdSCs, we trigger fate switching. Combining epigenetic, proteomic and functional analyses, we interrogate the ensuing chromatin and transcriptional dynamics, slowed temporally by the mature EpdSC niche microenvironment. We show that as SOX9 binds and opens key hair follicle enhancers de novo in EpdSCs, it simultaneously recruits co-factors away from epidermal enhancers, which are silenced. Unhinged from its normal regulation, sustained SOX9 subsequently activates oncogenic transcriptional regulators that chart the path to cancers typified by constitutive SOX9 expression.

TRPS1: A Marker of Follicular Differentiation

The trichorhinophalangeal syndrome type 1 (TRPS1) immunohistochemical (IHC) stain has increased in use in recent years as a marker for breast carcinomas. The TRPS1 gene is involved in various tissues, including the growth and differentiation of hair follicles. This article seeks to evaluate the IHC expression of TRPS1 in cutaneous neoplasms with follicular differentiation, such as trichoblastoma (TB), trichoepithelioma (TE), and basal cell carcinoma (BCC). IHC studies were performed on 13 TBs, 15 TEs, and 15 BCCs with an antibody against TRPS1. The study found a variable staining expression of TRPS1 in the tumor nests of TB, TE, and BCC. BCCs were distinct in that none of the BCCs demonstrated intermediate or high positivity, while TBs and TEs showed intermediate-to-high positivity in 5/13 (38%) and 3/15 (20%) of cases, respectively. We observed a distinct staining pattern among the mesenchymal cells of TB and TE. We found that TRPS1 highlighted perifollicular mesenchymal cells adjacent to the nests of TB and TE tumor cells. This staining pattern was absent in BCCs, where only scattered stromal cells were positive for TRPS1. Papillary mesenchymal bodies were also highlighted by TRPS1 in TB and TE. TRPS1 stained various parts of the normal hair follicle, including the nuclei of cells in the germinal matrix, outer root sheaths, and hair papillae. TRPS1 may be a useful IHC marker for follicular differentiation.

c-FOS Expression in Metastatic Basal Cell Carcinoma with Spontaneous Basosquamous Transition

Abstract is missing (Short communication)

Recurrence or de novo? Intradermal Basal Cell Carcinoma of the Scrotum: A Report of Two Cases

Basal cell carcinoma (BCC) is the most common cutaneous malignancy, usually occurring in sun-exposed areas. Although BCC in the scrotal region is uncommon, it carries a higher risk of metastasis than BCC at other sites. Here, we report two cases of BCC that developed in the scrotal region: Case 1 presented as a superficial nodule and Case 2 as a subcutaneous nodule. Histopathologically, both tumors lacked continuity with the surface epidermis and formed an intradermal nodule. In Case 1, BCC occurred for the first time and presumably developed de novo. Case 2 underwent excision of a scrotal BCC 5 years previously, and the histopathological diagnosis at that time was nodular BCC. However, when the original specimen was re-examined, it was determined that, although the tumor had been completely resected, part of the lesion had moved away from the nodular area to represent a micronodular phenotype, an aggressive BCC subtype. We hypothesized that partial evolution from a nodular to a micronodular phenotype may have contributed to the recurrence of BCC in Case 2.

Clinical and pathological features associated with high-risk, multiple, and recurrent basal cell carcinomas: a retrospective cohort analysis from the Levantine coast of the Mediterranean Sea

Basal cell carcinoma (BCC) data coming from the Levantine coast of the Mediterranean Sea are limited. The study aimed to primarily analyze the demographic, clinical, pathological, and prognostic characteristics of BCC in this region of the world and secondarily identify features associated with high-risk, recurrent, or multiple BCCs. Patients with at least one diagnosis of BCC registered in the pathology department between January 2015 and December 2019 were included in this analytical retrospective single-center cohort study. Patients with basal cell nevus syndrome were excluded. Patients' characteristics and pathological features were collected through file check for a first analysis. Risk factors and evolution were sought through a phone call interview for the second analysis. The first analysis included 506 BCCs corresponding to 365 patients with a mean age of 65 ± 15 years, twenty-two (6%) were less than 40 years old, 180 (49.3%) were women, and 85 (23.3%) had two or more BCCs. The second analysis included 279 BCCs corresponding to 205 patients. Periorificial and infiltrative BCCs were more frequent in men. Periorificial tumors were more frequently nodular or infiltrative and were associated with recurrence. Tumors with perineural involvement were histologically never nodular nor superficial. Recurrence was more frequent in BCCs having periorificial location, a size larger than 2 cm, or an infiltrative subtype. Multiple BCCs were more frequent in patients with light skin type or familial history of skin cancer. High-risk BCCs were more common in patients with low sun exposure.

Evolvability and emergence of tumor heterogeneity as a space-time function

The loss of control of cell proliferation, apoptosis regulation and contact inhibition leads to tumor development. While benign tumors are restricted to their primary space, i.e. where these tumors first originate, the metastatic tumors not only disseminate- facilitated by hypoxia-driven neovascularization- to distant secondary sites but also show substantial changes in metabolism, tissue architectures, gene expression profiles and immune phenotypes. All these alterations result in radio-, chemo- and immune-resistance rendering these metastatic tumor cells refractory to therapy. Since the beginning of the transformation, these factors- which influence each other- are incorporated to the developing and metastasizing tumor. As a result, the complexities in the heterogeneity of tumor progressively increase. This space-time function in the heterogeneity of tumors is generated by various conditions and factors at the genetic as well as microenvironmental levels, for example, endogenous retroviruses, methylation and epigenetic dysregulation that may be etiology-specific, cancer associated inflammation, remodeling of the extracellular matrix and mesenchymal cell shifted functions. On the one hand, these factors may cause de-differentiation of the tumor cells leading to cancer stem cells that contribute to radio-, chemo- and immune-resistance and recurrence of tumors. On the other hand, they may also enhance the heterogeneity under specific microenvironment-driven proliferation. In this editorial, we intend to underline the importance of heterogeneity in cancer progress, its evaluation and its use in correlation with the tumor evolution in a specific patient as a field of research for achieving precise patient-tailored treatments and amelioration of diagnostic (monitoring) tools and prognostic capacity.

[Current Management of Basal Cell Carcinoma]

AIM OF STUDY

We present the current standard in diagnosis and treatment of basal cell carcinoma. Useful procedures for clinical management should be derived from this.

METHODS

A systematic literature search was carried out in the PubMed online database. The collected information was analyzed and evaluated. An overall concept was created from the gained knowledge.

RESULTS

Basal cell carcinoma is the most common tumor in humans and its incidence is expected to increase in the future. When managing the disease, a one-dimensional orientation towards the clinical or histological subtype is not sufficient because of the heterogeneity of the tumor. The primary implementation of risk stratification, which is decisive for the further diagnostic and therapeutic steps, is becoming increasingly important. The gold standard in treatment continues to be the surgical procedure, which should be carried out using micrographically controlled surgery if possible. In addition, there are other therapeutic methods such as radiotherapy or a number of topical therapy options (photodynamic therapy, cryotherapy, application of 5-fluorouracil or imiquimod), which can be used in certain cases. Hedgehog inhibitors are also effective drugs for advanced or metastatic basal cell carcinoma. Practitioners have gained several years of experience with regard to effectiveness and handling of adverse events. With the PD-1 inhibitor cemiplimab, another therapeutic option for inoperable or metastatic tumors has been available since June 2021.

CONCLUSION

Basal cell carcinoma will continue to gain in relevance in daily dermatological practice in the coming years. A structured approach to the assessment of the existing risk category of the tumor and the subsequent determination of the optimal therapy regimen are of central importance. Advanced or metastatic tumors no longer represent a hopeless situation for the patient. With long-termhedgehog therapy, an adapted dosage scheme can avoid discontinuation of therapy due to side effects. The therapeutic potential of the PD-1 inhibitor cemiplimab can also be used with the side effect profile known from other types of skin cancer.

CD200 ectodomain shedding into the tumor microenvironment leads to NK cell dysfunction and apoptosis

The basis of immune evasion, a hallmark of cancer, can differ even when cancers arise from one cell type such as in the human skin keratinocyte carcinomas: basal and squamous cell carcinoma. Here we showed that the basal cell carcinoma tumor-initiating cell surface protein CD200, through ectodomain shedding, was responsible for the near absence of NK cells within the basal cell carcinoma tumor microenvironment. In situ, CD200 underwent ectodomain shedding by metalloproteinases MMP3 and MMP11, which released biologically active soluble CD200 into the basal cell carcinoma microenvironment. CD200 bound its cognate receptor on NK cells to suppress MAPK pathway signaling that in turn blocked indirect (IFN-γ release) and direct cell killing. In addition, reduced ERK phosphorylation relinquished negative regulation of PPARγ-regulated gene transcription and led to membrane accumulation of the Fas/FADD death receptor and its ligand, FasL, which resulted in activation-induced apoptosis. Blocking CD200 inhibition of MAPK or PPARγ signaling restored NK cell survival and tumor cell killing, with relevance to many cancer types. Our results thus uncover a paradigm for CD200 as a potentially novel and targetable NK cell-specific immune checkpoint, which is responsible for NK cell-associated poor outcomes in many cancers.

The Use of Retinoids for the Prevention and Treatment of Skin Cancers: An Updated Review

Retinoids are natural and synthetic vitamin A derivatives that are effective for the prevention and the treatment of non-melanoma skin cancers (NMSC). NMSCs constitute a heterogenous group of non-melanocyte-derived skin cancers that impose substantial burdens on patients and healthcare systems. They include entities such as basal cell carcinoma and cutaneous squamous cell carcinoma (collectively called keratinocyte carcinomas), cutaneous lymphomas and Kaposi’s sarcoma among others. The retinoid signaling pathway plays influential roles in skin physiology and pathology. These compounds regulate diverse biological processes within the skin, including proliferation, differentiation, angiogenesis and immune regulation. Collectively, retinoids can suppress skin carcinogenesis. Both topical and systemic retinoids have been investigated in clinical trials as NMSC prophylactics and treatments. Desirable efficacy and tolerability in clinical trials have prompted health regulatory bodies to approve the use of retinoids for NMSC management. Acceptable off-label uses of these compounds as drugs for skin cancers are also described. This review is a comprehensive outline on the biochemistry of retinoids, their activities in the skin, their effects on cancer cells and their adoption in clinical practice.

Molecular Mechanisms and Targeted Therapies of Advanced Basal Cell Carcinoma

Among human cutaneous malignancies, basal cell carcinoma is the most common. Solid advances in unveiling the molecular mechanisms of basal cell carcinoma have emerged in recent years. In Gorlin syndrome, which shows basal cell carcinoma predisposition, identification of the patched 1 gene (PTCH1) mutation was a dramatic breakthrough in understanding the carcinogenesis of basal cell carcinoma. PTCH1 plays a role in the hedgehog pathway, and dysregulations of this pathway are known to be crucial for the carcinogenesis of many types of cancers including sporadic as well as hereditary basal cell carcinoma. In this review, we summarize the clinical features, pathological features and hedgehog pathway as applied in basal cell carcinoma. Other crucial molecules, such as p53 and melanocortin-1 receptor are also discussed. Due to recent advances, therapeutic strategies based on the precise molecular mechanisms of basal cell carcinoma are emerging. Target therapies and biomarkers are also discussed.

Hedgehog signaling mechanism and role in cancer

Cell-cell communication through evolutionarily conserved signaling pathways governs embryonic development and adult tissue homeostasis. Deregulation of these signaling pathways has been implicated in a wide range of human diseases including cancer. One such pathway is the Hedgehog (Hh) pathway, which was originally discovered in Drosophila and later found to play a fundamental role in human development and diseases. Abnormal Hh pathway activation is a major driver of basal cell carcinomas (BCC) and medulloblastoma. Hh exerts it biological influence through a largely conserved signal transduction pathway from the activation of the GPCR family transmembrane protein Smoothened (Smo) to the conversion of latent Zn-finger transcription factors Gli/Ci proteins from their repressor (GliR/CiR) to activator (GliA/CiA) forms. Studies from model organisms and human patients have provided deep insight into the Hh signal transduction mechanisms, revealed roles of Hh signaling in a wide range of human cancers, and suggested multiple strategies for targeting this pathway in cancer treatment.

Differentiation of crescent-forming kidney progenitor cells into podocytes attenuates severe glomerulonephritis in mice

Crescentic glomerulonephritis is characterized by vascular necrosis and parietal epithelial cell hyperplasia in the space surrounding the glomerulus, resulting in the formation of crescents. Little is known about the molecular mechanisms driving this process. Inducing crescentic glomerulonephritis in two Pax2Cre reporter mouse models revealed that crescents derive from clonal expansion of single immature parietal epithelial cells. Preemptive and delayed histone deacetylase inhibition with panobinostat, a drug used to treat hematopoietic stem cell disorders, attenuated crescentic glomerulonephritis with recovery of kidney function in the two mouse models. Three-dimensional confocal microscopy and stimulated emission depletion superresolution imaging of mouse glomeruli showed that, in addition to exerting an anti-inflammatory and immunosuppressive effect, panobinostat induced differentiation of an immature hyperplastic parietal epithelial cell subset into podocytes, thereby restoring the glomerular filtration barrier. Single-cell RNA sequencing of human renal progenitor cells in vitro identified an immature stratifin-positive cell subset and revealed that expansion of this stratifin-expressing progenitor cell subset was associated with a poor outcome in human crescentic glomerulonephritis. Treatment of human parietal epithelial cells in vitro with panobinostat attenuated stratifin expression in renal progenitor cells, reduced their proliferation, and promoted their differentiation into podocytes. These results offer mechanistic insights into the formation of glomerular crescents and demonstrate that selective targeting of renal progenitor cells can attenuate crescent formation and the deterioration of kidney function in crescentic glomerulonephritis in mice.

The Contributions of Cancer-Testis and Developmental Genes to the Pathogenesis of Keratinocyte Carcinomas

Simple Summary

In addition to mutations, ectopically-expressed genes are emerging as important contributors to cancer development. Efforts to characterize the expression patterns in cancers of gamete-restricted cancer-testis antigens and developmentally-restricted genes are underway, revealing these genes to be putative biomarkers and therapeutic targets for various malignancies. Basal cell carcinoma (BCC) and cutaneous squamous cell carcinoma (cSCC) are two highly-prevalent non-melanoma skin cancers that result in considerable burden on patients and our health system. To optimize disease prognostication and treatment, it is necessary to further classify the molecular complexity of these malignancies. This review describes the expression patterns and functions of cancer-testis antigens and developmentally-restricted genes in BCC and cSCC tumors. A large number of cancer-testis antigens and developmental genes exhibit substantial expression levels in BCC and cSCC. These genes have been shown to contribute to several aspects of cancer biology, including tumorigenesis, differentiation, invasion and responses to anti-cancer therapy.

Abstract

Keratinocyte carcinomas are among the most prevalent malignancies worldwide. Basal cell carcinoma (BCC) and cutaneous squamous cell carcinoma (cSCC) are the two cancers recognized as keratinocyte carcinomas. The standard of care for treating these cancers includes surgery and ablative therapies. However, in recent years, targeted therapies (e.g., cetuximab for cSCC and vismodegib/sonidegib for BCC) have been used to treat advanced disease as well as immunotherapy (e.g., cemiplimab). These treatments are expensive and have significant toxicities with objective response rates approaching ~50–65%. Hence, there is a need to dissect the molecular pathogenesis of these cancers to identify novel biomarkers and therapeutic targets to improve disease management. Several cancer-testis antigens (CTA) and developmental genes (including embryonic stem cell factors and fetal genes) are ectopically expressed in BCC and cSCC. When ectopically expressed in malignant tissues, functions of these genes may be recaptured to promote tumorigenesis. CTAs and developmental genes are emerging as important players in the pathogenesis of BCC and cSCC, positioning themselves as attractive candidate biomarkers and therapeutic targets requiring rigorous testing. Herein, we review the current research and offer perspectives on the contributions of CTAs and developmental genes to the pathogenesis of keratinocyte carcinomas.

Eight Years of Real-Life Experience with Smoothened Inhibitors in a Swiss Tertiary Skin Referral Center

Simple Summary

Vismodegib and sonidegib are targeted therapies inhibiting the hedgehog pathway, a key driver in the pathogenesis of basal cell carcinoma (BCC). Hedgehog inhibitors (HhIs) are first-line therapy for locally advanced basal cell carcinoma (laBCC), metastatic basal cell carcinoma (mBCC) and multiple BCCs, when surgery and radiotherapy are no longer feasible. Safety and efficacy of the HhIs vismodegib and sonidegib have been shown in large prospective clinical trials. However, treatment of advanced basal cell carcinoma (aBCC) in daily practice includes patients who do not meet strict inclusion criteria and poses an additional challenge for treating physicians. This study aims to give an insight into a real-world experience in our tertiary skin referral center.

Abstract

Background: The hedgehog inhibitors vismodegib and sonidegib are approved for the treatment of advanced basal cell carcinoma. This study reports the experiences with these therapies in a tertiary skin referral center in daily practice. Methods: A retrospective, observational, single-center study analyzing medical records of patients with aBCC treated with a smoothened (SMO) inhibitor outside a clinical trial for at least one month between 2013 and 2021. Results: In total, 33 patients were included: 21 (64%) patients were treated with vismodegib, 3 (9%) patients with sonidegib and 9 (27%) patients with both treatments subsequently. With vismodegib, the best overall response was complete response (CR) in 33% cases, and partial response (PR) in 33% cases. Under sonidegib, 42% patients achieved CR and 17% PR. Mean duration to next treatment was 33 and 14 months for vismodegib and sonidegib, respectively. Adverse events varied in frequency between continuous and intermittent dosing and they were the most common reason for therapy discontinuation. Conclusions: Our real-world data illustrate the pitfalls and benefits of HhIs as well as the impact of different dosing regimens on adverse events, patient adherence and response. Treatment duration remains limited by adverse events and resistance. Additional treatment options, including immunotherapy and drug combinations, are needed.

Basal cell carcinomas acquire secondary mutations to overcome dormancy and progress from microscopic to macroscopic disease

Basal cell carcinomas (BCCs) frequently possess immense mutational burdens; however, the functional significance of most of these mutations remains unclear. Here, we report that loss of Ptch1, the most common mutation that activates upstream Hedgehog (Hh) signaling, initiates the formation of nascent BCC-like tumors that eventually enter into a dormant state. However, rare tumors that overcome dormancy acquire the ability to hyperactivate downstream Hh signaling through a variety of mechanisms, including amplification of Gli1/2 and upregulation of Mycn. Furthermore, we demonstrate that MYCN overexpression promotes the progression of tumors induced by loss of Ptch1. These findings suggest that canonical mutations that activate upstream Hh signaling are necessary, but not sufficient, for BCC to fully progress. Rather, tumors likely acquire secondary mutations that further hyperactivate downstream Hh signaling in order to escape dormancy and enter a trajectory of uncontrolled expansion.

Trieu et al. generate BCC mouse models in which rare macroscopic tumors form alongside numerous failed microscopic lesions. Successful macroscopic tumors acquire secondary changes that elevate Gli1, Gli2, and/or Mycn levels, causing hyperactivation of downstream Hedgehog (Hh) signaling. Loss of p53 and Notch1 also contributes to tumor progression.

Cellular Heterogeneity and Plasticity of Skin Epithelial Cells in Wound Healing and Tumorigenesis

Cellular differentiation, the fundamental hallmark of cells, plays a critical role in homeostasis. And stem cells not only regulate the process where embryonic stem cells develop into a complete organism, but also replace ageing or damaged cells by proliferation, differentiation and migration. In characterizing distinct subpopulations of skin epithelial cells, stem cells show large heterogeneity and plasticity for homeostasis, wound healing and tumorigenesis. Epithelial stem cells and committed progenitors replenish each other or by themselves owing to the remarkable plasticity and heterogeneity of epidermal cells under certain circumstance. The development of new assay methods, including single-cell RNA sequence, lineage tracing assay, intravital microscopy systems and photon-ablation assay, highlight the plasticity of epidermal stem cells in response to injure and tumorigenesis. However, the critical mechanisms and key factors that regulate cellular plasticity still need for further exploration. In this review, we discuss the recent insights about the heterogeneity and plasticity of epithelial stem cells in homeostasis, wound healing and skin tumorigenesis. Understanding how stem cells collaborate together to repair injury and initiate tumor will offer new solutions for relevant diseases. Schematic abstract of cellular heterogeneity and plasticity of skin epithelial cells in wound healing and tumorigenesis.

Murine Models for Lineage Tracing Cancer Initiating Cells

The process of cellular transformation involves acquisition of genetic mutations that disrupt parenchymal organization and promote unrestrained epithelial cell proliferation. In the context of transformation, recent advances using genetic lineage tracing have enabled scientists to study the behavior of neoplastic cells in their native habitat. Employing lineage tracing to understand mechanisms of transformation, including cell type-specific responses to inflammation, is an empirical method to use in the field of cancer prevention. Identifying new approaches to prevent cancer formation can be directly studied by indelibly labeling cells to trace their fate and understand at a molecular level how they respond to novel methods for testing cancer preventing agents.

Aktuelles Management des Basalzellkarzinoms

Ziel der Studie Der aktuelle Standard von Diagnostik und Therapie des Basalzellkarzinoms soll dargestellt werden. Hieraus sollen sinnvolle Vorgehensweisen für das klinische Management abgeleitet werden.

Methodik Es erfolgte eine systematische Literaturrecherche in der Online-Datenbank PubMed. Die gesammelten Informationen wurden analysiert und bewertet. Aus den gewonnenen Erkenntnissen wurde ein Gesamtkonzept erstellt.

Ergebnisse Das Basalzellkarzinom ist der häufigste Tumor des Menschen und die Inzidenz wird voraussichtlich künftig weiter zunehmen. Beim Management der Erkrankung wird eine eindimensionale Orientierung am klinischen bzw. histologischen Basalzellkarzinom-Subtyp der Heterogenität des Tumors nicht gerecht. Zunehmende Bedeutung gewinnt die primäre Durchführung einer Risikostratifizierung, die für die weiteren diagnostischen und therapeutischen Schritte maßgeblich ist. Goldstandard in der Behandlung bleibt weiterhin das operative Vorgehen, welches möglichst mittels mikrografisch kontrollierter Chirurgie erfolgen sollte. Daneben existieren weitere Therapieverfahren wie die Radiotherapie oder eine Reihe an topischen Therapieoptionen (photodynamische Therapie, Kryotherapie oder Applikation von 5-Fluoruracil bzw. Imiquimod), die in bestimmten Fällen zur Anwendung kommen können. Auch für fortgeschrittene oder metastasierte Basalzellkarzinome stehen mit den Hedgehog-Inhibitoren wirksame Medikamente zur Verfügung, für die inzwischen eine mehrjährige Anwendungserfahrung hinsichtlich Wirksamkeit und Umgang mit unerwünschten Ereignissen vorliegt. Mit den PD-1-Inhibitoren steht eine weitere systemische Therapieoption in Aussicht, deren Nutzen aktuell noch in klinischen Studien überprüft wird.

Schlussfolgerung Das Basalzellkarzinom wird in den kommenden Jahren weiter an Relevanz in der täglichen dermatologischen Praxis gewinnen. Eine strukturierte Herangehensweise zur Einschätzung der vorliegenden Risikokategorie des Tumors und die anschließende Festlegung des optimalen Therapieregimes sind von zentraler Bedeutung. Fortgeschrittene oder metastasierte Tumoren stellen keine aussichtslose Situation für den Patienten mehr dar. Durch adaptierte Dosierschemata kann ein nebenwirkungsbedingter Therapieabbruch unter langfristiger Hedgehog-Therapie vermieden werden. Das therapeutische Potenzial von PD-1-Inhibitoren könnte bald auch beim Basalzellkarzinom genutzt werden.

Novel PTCH1 and concurrent TP53 mutations in four patients with numerous non-syndromic basal cell carcinomas: The paradigm of oncogenic synergy

There has been a significant increase in basal cell carcinoma (BCC) incidence, the most common cancer in humans and the age of presentation with the first diagnosis of BCC has decreased in past decades. In this study, we investigated the possibility of genetic markers that can lead to earlier and closer observation of patients at high risk for development of multiple BCCs. The overall goal is to decrease the morbidity and the economic burden of diagnosis and treatment of recurring and/or advanced BCCs. Four patients with numerous BCCs, some of them exceptionally large, were included in this study. A sample of representative BCCs, normal non-sun-exposed skin and blood samples were obtained from each patient. Whole-exome sequencing of DNA was conducted on all samples, and a series of bioinformatics filtering was performed to identify potentially pathogenic sequence variants. The analysis of the data resulted in detection of oncogenic mutations in PTCH1, two of which being novel, and concurrent mutations in TP53 in BCC tumours of all four patients. Such mutations may explain the numerous and postexcision recurring nature of the BCCs of exceptionally large size observed in all these patients, and they can be suggested to serve as a genetic marker for high-risk patients for early detection, prognostication and close follow-up.

Aryl hydrocarbon receptor controls skin homeostasis, regeneration, and hair follicle cycling by adjusting epidermal stem cell function

Skin integrity requires constant maintenance of a quiescent, yet responsive, population of stem cells. While interfollicular epidermal progenitors control normal homeostasis, hair follicle stem cells residing within the bulge provide regenerative potential during hair cycle and in response to wounding. The aryl hydrocarbon receptor (AhR) modulates cell plasticity and differentiation and its overactivation results in severe skin lesions in humans. However, its physiological role in skin homeostasis and hair growth is unknown. Reconstitution assays grafting primary keratinocytes and dermal fibroblasts into nude mice and 3-D epidermal equivalents revealed a positive role for AhR in skin regeneration, epidermal differentiation, and stem cell maintenance. Furthermore, lack of receptor expression in AhR-/- mice delayed morphogenesis and impaired hair regrowth with a phenotype closely correlating with a reduction in suprabasal bulge stem cells (α6^low CD34⁺ ). Moreover, RNA-microarray and RT-qPCR analyses of fluorescence-activated cell sorting (FACS)-isolated bulge stem cells revealed that AhR depletion impaired transcriptional signatures typical of both epidermal progenitors and bulge stem cells but upregulated differentiation markers likely compromising their undifferentiated phenotype. Altogether, our findings support that AhR controls skin regeneration and homeostasis by ensuring epidermal stem cell identity and highlights this receptor as potential target for the treatment of cutaneous pathologies.

Known and new facts on basal cell carcinoma

Basal cell carcinoma (BCC) is the most common malignant tumor in light‐skinned people and amounts to about 75 % of all cases of skin cancer. Increasing incidence rates have been reported for decades all over the world. The main risk factors include UV radiation, male sex, light skin type, advanced age, long‐term immunosuppression, a positive individual or family history, and certain genodermatoses. BCC metastasizes only rarely, and its mortality is low, but it is associated with significant morbidity. Genetic mutations especially in the hedgehog pathway play an important role in BCC pathogenesis. Non‐invasive procedures such as optical coherence tomography or confocal laser scan microscopy are increasingly utilized for diagnostics in addition to visual inspection and dermatoscopy, but only in exceptional cases can histological confirmation of the diagnosis be dispensed with. Various clinical and histological subtypes have been defined. Differentiating between BCC with high and low risk of recurrence has a significant influence on the choice of treatment. Most BCC can be treated effectively and safely with standard surgery, or in selected cases with topical treatment. Locally advanced and metastasized BCC must be treated with radiation or systemic therapy. Radiation is also an option for older patients with contraindications for surgery. The hedgehog inhibitors vismodegib and sonidegib are currently approved for systemic therapy of BCC in Europe. Approval for the PD1 inhibitor cemiplimab as second‐line therapy is expected in the near future.

Oncogenic Hedgehog-smoothened signaling depends on YAP1-TAZ/TEAD transcription to restrain differentiation in basal cell carcinoma

Disruption of the transcriptional activity of the Hippo pathway members YAP1 and TAZ has become a major target for cancer treatment. However, detailed analysis of the effectivity and networks affected by YAP1/TAZ transcriptional targeting are limited. Here, we utilize TEADi, an inhibitor of the binding of YAP1 and TAZ with their main transcriptional target TEAD in a mouse model of basal cell carcinoma (BCC) to unveil the consequences of YAP1/TAZ transcriptional inhibition in cancer cells. Both TEADi and YAP1/TAZ knockdown lead to reduced proliferation and increased differentiation of mouse BCC driven by oncogenic Hedgehog-Smoothened (SmoM2) activity. While TEAD transcriptional networks were essential to inactivate differentiation in BCC, this inactivation was found to be indirect and potentially mediated through the repression of KLF4 by SNAI2. By comparing the transcriptional effects of TEADi with those caused by YAP1/TAZ depletion, we determined YAP1/TAZ TEAD-independent effects in cancer cells that impact STAT3 and NF-κB. Our results reveal the gene networks affected by targeting YAP1/TAZ-TEAD in BCC tumors and expose potential pitfalls for targeting TEAD transcription in cancer.

Aspects of the Tumor Microenvironment Involved in Immune Resistance and Drug Resistance

The tumor microenvironment (TME) is a complex and ever-changing "rogue organ" composed of its own blood supply, lymphatic and nervous systems, stroma, immune cells and extracellular matrix (ECM). These complex components, utilizing both benign and malignant cells, nurture the harsh, immunosuppressive and nutrient-deficient environment necessary for tumor cell growth, proliferation and phenotypic flexibility and variation. An important aspect of the TME is cellular crosstalk and cell-to-ECM communication. This interaction induces the release of soluble factors responsible for immune evasion and ECM remodeling, which further contribute to therapy resistance. Other aspects are the presence of exosomes contributed by both malignant and benign cells, circulating deregulated microRNAs and TME-specific metabolic patterns which further potentiate the progression and/or resistance to therapy. In addition to biochemical signaling, specific TME characteristics such as the hypoxic environment, metabolic derangements, and abnormal mechanical forces have been implicated in the development of treatment resistance. In this review, we will provide an overview of tumor microenvironmental composition, structure, and features that influence immune suppression and contribute to treatment resistance.

Differential expression of phosphorylated MEK and ERK correlates with aggressive BCC subtypes

Basal cell carcinoma (BCC) is associated with aberrant Hedgehog (HH) signalling through mutational inactivation of PTCH1; however, there is conflicting data regarding MEK/ERK signalling in BCC and the signalling pathway interactions in these carcinomas. To address this, expression of active phospho (p) MEK and ERK was examined in a panel of 15 non-aggressive and 14 aggressive BCCs. Although not uniformly expressed, both phospho-proteins were detected in the nuclei and/or cytoplasm of normal and tumour-associated epidermal cells however, whereas phospho-MEK (pMEK) was present in all non-aggressive BCCs (14/14), phospho-ERK (pERK) was rarely expressed (2/14). In contrast pERK expression was more prevalent in aggressive tumours (11/14). Interestingly, pMEK was only localized to the tumour mass whereas pERK was expressed in tumours and stroma of aggressive BCCs. Similarly, pERK (but not pMEK) was absent in mouse BCC-like tumours derived from X-ray irradiated Ptch1+/- mice with stromal pERK observed in myofibroblasts of the aggressive variant as well as in the tumour mass. RNA sequencing analysis of tumour epithelium and stroma of aggressive and non-aggressive BCC revealed the upregulation of epidermal growth factor receptor- and ERK-related pathways. Angiogenesis and immune response pathways were also upregulated in the stroma compared with the tumour. PTCH1 suppressed NEB1 immortalized keratinocytes (shPTCH1) display upregulated pERK that can be independent of MEK expression. Furthermore, epidermal growth factor pathway inhibitors affect the HH pathway by suppressing GLI1. These studies reveal differential expression of pERK between human BCC subtypes that maybe active by a pathway independent of MEK.

Expert opinion on sonidegib efficacy, safety and tolerability

Introduction: Hedgehog inhibitors are an alternative treatment option for patients with advanced BCCs not eligible for standard therapies due to lack of efficacy, high recurrence risk, and high-rate morbidity. Sonidegib, an oral smoothened antagonist, has been approved for the treatment of adult patients with locally advanced basal cell carcinoma. Several studies and randomized controlled trials have been conducted in order to evaluate the efficacy, safety, and tolerability of this new molecule.Areas covered: The aim of this article is to provide a complete overview on the use of sonidegib for the treatment of advanced BCCs describing the efficacy, safety, and drug tolerability of this drug.Expert opinion: Sonidegib, with a different pharmacokinetics profile from that of the other SMO-inhibitor vismodegib, demonstrated to be an efficacious and well-tolerated treatment in patients with locally advanced BCC. Although several drug-related adverse events have already been described, different strategies should be taken into account to better manage this small molecule while avoiding treatment discontinuation. The use of sonidegib as neoadjuvant therapy or combined with other hedgehog pathway inhibitors targeting different sites and to date, only available for pre-clinical studies, should also be considered.

Regional Variation in Epidermal Susceptibility to UV-Induced Carcinogenesis Reflects Proliferative Activity of Epidermal Progenitors

To better understand the influence of ultraviolet (UV) irradiation on the initial steps of skin carcinogenesis, we examine patches of labeled keratinocytes as a proxy for clones in the interfollicular epidermis (IFE) and measure their size variation upon UVB irradiation. Multicolor lineage tracing reveals that in chronically irradiated skin, patches near hair follicles (HFs) increase in size, whereas those far from follicles do not change. This is explained by proliferation of basal epidermal cells within 60 μm of HF openings. Upon interruption of UVB, patch size near HFs regresses significantly. These anatomical differences in proliferative behavior have significant consequences for the cell of origin of basal cell carcinomas (BCCs). Indeed, a UV-inducible murine BCC model shows that BCC patches are more frequent, larger, and more invasive near HFs. These findings have major implications for the prevention of field cancerization in the epidermis.

Involvement of transcribed lncRNA uc.291 and SWI/SNF complex in cutaneous squamous cell carcinoma

While non-melanoma skin cancers (NMSCs) are the most common tumours in humans, only the sub-type cutaneous squamous cell carcinoma (cSCC), might become metastatic with high lethality. We have recently identified a regulatory pathway involving the lncRNA transcript uc.291 in controlling the expression of epidermal differentiation complex genes via the interaction with ACTL6A, a component of the chromatin remodelling complex SWI/SNF. Since transcribed ultra-conserved regions (T-UCRs) are expressed in normal tissues and are deregulated in tumorigenesis, here we hypothesize a potential role for dysregulation of this axis in cSCC, accounting for the de-differentiation process observed in aggressive poorly differentiated cutaneous carcinomas. We therefore analysed their expression patterns in human tumour biopsies at mRNA and protein levels. The results suggest that by altering chromatin accessibility of the epidermal differentiation complex genes, down-regulation of uc.291 and BRG1 expression contribute to the de-differentiation process seen in keratinocyte malignancy. This provides future direction for the identification of clinical biomarkers in cutaneous SCC. Analysis of publicly available data sets indicates that the above may also be a general feature for SCCs of different origins.

Cellular heterogeneity and microenvironmental control of skin cancer

Healthy tissues harbour a surprisingly high number of cells that carry well-known cancer-causing mutations without impacting their physiological function. In recent years, strong evidence accumulated that the immediate environment of mutant cells profoundly impact their prospect of malignant progression. In this review, focusing on the skin, we investigate potential key mechanisms that ensure tissue homeostasis despite the presence of mutant cells, as well as critical factors that may nudge the balance from homeostasis to tumour formation. Functional in vivo studies and single-cell transcriptome analyses have revealed a tremendous cellular heterogeneity and plasticity within epidermal (stem) cells and their respective niches, revealing for example wild-type epithelial cells, fibroblasts or immune-cell subsets as critical in preventing cancer formation and malignant progression. It's the same cells, however, that can drive carcinogenesis. Therefore, understanding the abundance and molecular variation of cell types in health and disease, and how they interact and modulate the local signalling environment will thus be key for new therapeutic avenues in our battle against cancer.

Adhesion Molecules in Non-melanoma Skin Cancers: A Comprehensive Review

Basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) are the most frequently diagnosed cancers, generating significant medical and financial problems. Cutaneous carcinogenesis is a very complex process characterized by genetic and molecular alterations, and mediated by various proteins and pathways. Cell adhesion molecules (CAMs) are transmembrane proteins responsible for cell-to-cell and cell-to-extracellular matrix adhesion, engaged in all steps of tumor progression. Based on their structures they are divided into five major groups: cadherins, integrins, selectins, immunoglobulins and CD44 family. Cadherins, integrins and CD44 are the most studied in the context of non-melanoma skin cancers. The differences in expression of adhesion molecules may be related to the invasiveness of these tumors, through the loss of tissue integrity, neovascularization and alterations in intercellular signaling processes. In this article, each group of CAMs is briefly described and the present knowledge on their role in the development of non-melanoma skin cancers is summarized.

HLA-G, cytokines, and cytokine receptors in the non-aggressive basal cell carcinoma microenvironment

Non-aggressive basal cell carcinoma (BCC) growth is slow and might be mediated by the immune system. This study analysed the human leukocyte antigen (HLA)-G expression and cytokine profile in non-aggressive BCC subtypes from distinct locations. HLA-G was evaluated via immunohistochemistry and cytokine expression was analysed by a quantitative real-time polymerase chain reaction in 26 primary BCC samples, including nodular BCC (nBCC, n = 16) and superficial BCC (n = 10) from cephalic (ceBCC, n = 12) and non-cephalic (n = 14) locations, and by bioinformatics analysis of public GEO databases. Inflammatory infiltrate was concentrated around the tumour nests. HLA-G-positive inflammatory cells (53.85%) were more abundant than HLA-G-positive tumour cells (21.54%, p < 0.001). HLA-G immunoreactivity was predominantly cytoplasmic in BCC cells and was primarily associated with lymphocytes and macrophages surrounding the tumour. nBCC showed a higher percentage of HLA-G-positive tumour cells (p = 0.04), and ceBCC showed stronger intensity (p = 0.04). IFN-gamma and IL-10 expression were 1.95 and 1.22-fold higher, respectively, relative to that in normal skin, with a positive correlation between them (r = 0.61; p = 0.002). IL-23 expression was higher in nBCC (p = 0.04) and positively correlated (r = 0.47; p = 0.05) with slight intensity of HLA-G-positive tumour cells. The up-regulation of IL23A and IL10RB and down-regulation of IFNGR1 and IL4R gene expression in BCC compared to levels in adjacent tissues were demonstrated in the GSE125285 dataset. The exhibited cytokine profile was consistent with the induction of HLA-G expression in non-aggressive BCC subtypes. HLA-G expression in tumour cells and inflammatory cells surrounding BCCs supports the generation of inhibitory signals on various immune cells that exert anti-tumour responses.

Distinct transcriptomic landscapes of cutaneous basal cell carcinomas and squamous cell carcinomas

The majority of non-melanoma skin cancer (NMSC) is cutaneous basal cell carcinoma (BCC) or squamous cell carcinoma (SCC), which are also called keratinocyte carcinomas, as both of them originate from keratinocytes. The incidence of keratinocyte carcinomas is over 5 million per year in the US, three-fold higher than the total incidence of all other types of cancer combined. While there are several reports on gene expression profiling of BCC and SCC, there are significant variations in the reported gene expression changes in different studies. One reason is that tumor-adjacent normal skin specimens were not included in many studies as matched controls. Furthermore, while numerous studies of skin stem cells in mouse models have been reported, their relevance to human skin cancer remains unknown. In this report, we analyzed gene expression profiles of paired specimens of keratinocyte carcinomas with their matched normal skin tissues as the control. Among several novel findings, we discovered a significant number of zinc finger encoding genes up-regulated in human BCC. In BCC, a novel link was found between hedgehog signaling, Wnt signaling, and the cilium. While the SCC cancer-stem-cell gene signature is shared between human and mouse SCCs, the hair follicle stem-cell signature of mice was not highly represented in human SCC. Differential gene expression (DEG) in human BCC shares gene signature with both bulge and epidermal stem cells. We have also determined that human BCCs and SCCs have distinct gene expression patterns, and some of them are not fully reflected in current mouse models.

Differentiation of Basal Cell Carcinoma and Trichoepithelioma: An Immunohistochemical Study

ABSTRACT

Basal cell carcinoma (BCC) is the most common malignancy of the skin. It is an epithelial neoplasm with origin in the precursor cells of the interfollicular epidermis. Even though it has low metastatic potential, delay in management may lead to local destruction and morbidity. In contrast, trichoepithelioma (TE) is a benign tumor originating from the outer root sheath of the hair follicle. Similar to BCC, TE tends to affect the head and neck region. Both neoplasms may exhibit clinical and histopathological similarities, making them prone to misdiagnosis. Multiple immunomarkers have been used to distinguish among these entities, but so far, no single agent or combination of agents appear to be neither sensitive nor specific enough to differentiate between them. This study was divided into 2 parts. First, 17 cases of BCC and 14 cases of TE were stained with androgen receptor and bcl-2. Then, 27 cases of borderline/equivocal of BCC and 13 cases of borderline/equivocal TE were stained with the same protocol. Sensitivity and specificity were calculated for each individual immunomarker and for the combination of them. Androgen receptor positivity was 100% specific for BCC and borderline/equivocal BCC, whereas bcl-2 diffuse staining pattern demonstrated a sensitivity of 82.4% for BCC and 88.9% borderline/equivocal BCC. When both immunomarkers were combined, the sensitivity for BCC decreased (70.6%) but the specificity remained high (100%). Similarly, the sensitivity for borderline/equivocal BCC was 55.6%, whereas the specificity was 100%. Although moderately sensitive, combining both immunomarkers showed an excellent specificity to discriminate between BCC and TE.