Evaluation of the role of AXL in fusion-positive pediatric rhabdomyosarcoma identifies the small-molecule inhibitor bemcentinib (BGB324) as potent chemosensitizer

Rhabdomyosarcoma (RMS) is a highly aggressive pediatric cancer with features of skeletal muscle differentiation. Over 80% of the high-risk patients ultimately fail to respond to chemotherapy treatment, leading to limited therapeutic options and dismal prognostic rates. The lack of response - and subsequent tumor recurrence - is driven in part by stem cell-like cells, the tumor subpopulation that is enriched after treatment, and characterized by expression of the AXL receptor tyrosine kinase (AXL). AXL mediates survival, migration and therapy resistance in several cancer types; however, its function in RMS remains unclear. In this study, we investigated the role of AXL in RMS tumorigenesis, migration and chemotherapy response, and whether targeting of AXL with small molecule inhibitors could potentiate the efficacy of chemotherapy. We show that AXL is expressed in a heterogeneous manner in patient-derived xenografts (PDXs), primary cultures and cell line models of RMS, consistent with its stem-cell-state selectivity. By generating a CRISPR/Cas9 AXL knock-out and overexpressing models, we show that AXL contributes to the migratory phenotype of RMS, but not to chemotherapy resistance. Instead, pharmacological blockade with the AXL inhibitors bemcentinib (BGB324), cabozantinib and NPS-1034 rapidly killed RMS cells in an AXL-independent manner, and augmented the efficacy of the chemotherapeutics vincristine and cyclophosphamide. In vivo administration of the combination of bemcentinib and vincristine exerted strong anti-tumoral activity in a rapidly progressing PDX mouse model, significantly reducing tumor bruden compared to single-agent treatment. Collectively, our data identify bemcentinib as a promising drug to improve chemotherapy efficacy in RMS patients.

MYOD-SKP2 axis boosts tumorigenesis in fusion negative rhabdomyosarcoma by preventing differentiation through p57Kip2 targeting

Rhabdomyosarcomas (RMS) are pediatric mesenchymal-derived malignancies encompassing PAX3/7-FOXO1 Fusion Positive (FP)-RMS, and Fusion Negative (FN)-RMS with frequent RAS pathway mutations. RMS express the master myogenic transcription factor MYOD that, whilst essential for survival, cannot support differentiation. Here we discover SKP2, an oncogenic E3-ubiquitin ligase, as a critical pro-tumorigenic driver in FN-RMS. We show that SKP2 is overexpressed in RMS through the binding of MYOD to an intronic enhancer. SKP2 in FN-RMS promotes cell cycle progression and prevents differentiation by directly targeting p27Kip1 and p57Kip2, respectively. SKP2 depletion unlocks a partly MYOD-dependent myogenic transcriptional program and strongly affects stemness and tumorigenic features and prevents in vivo tumor growth. These effects are mirrored by the investigational NEDDylation inhibitor MLN4924. Results demonstrate a crucial crosstalk between transcriptional and post-translational mechanisms through the MYOD-SKP2 axis that contributes to tumorigenesis in FN-RMS. Finally, NEDDylation inhibition is identified as a potential therapeutic vulnerability in FN-RMS.

Abstract 3104: PAX3-FOXO1 increases fibroblast reprogramming efficiency and drives self-renewal in alveolar rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children. Most alveolar (ARMS) cases bear the chimeric transcription factor PAX3/7-FOXO1 and have a worse prognosis compared to the embryonal subtype (ERMS). Previous studies identified a CSC subpopulation in ERMS but no study looked at the translocation positive RMS so far. This knowledge would be important to guide future treatment strategies. Here, we show that no CSC subpopulation can be detected in ARMS by a range of common methods. Furthermore, in vivo limiting dilution experiments confirmed that even 100 ARMS cells are sufficient to generate tumors in NOD/SCID mice. Thus, we hypothesized that ARMS follows a clonal evolution model. In line with this hypothesis, the stem cell factors Nanog, Oct4, and Sox2 were homogeneously expressed in ARMS cell lines and genetic loss- or gain-of-function experiments did not change cellular physiology unlike silencing of PAX3-FOXO1 which caused cell cycle arrest and apoptosis. Based on these observations we then investigated whether PAX3-FOXO1 itself can act as stem cell gene. For this we reprogrammed human fibroblast with the known factors Oct4, Sox2, Klf4, and c-Myc in presence or absence of PAX3-FOXO1. Interestingly, the presence of the fusion protein significantly increased the reprogramming efficiency leading to the generation of almost double the number of colonies of induced pluripotent stem cells (iPSC) than the control cells. PAX3-FOXO1 iPSC expressed the core stem cell genes as well as the PAX3-FOXO1 target gene AP2beta. Strikingly, PAX3-FOXO1 iPSC showed reduced ability to differentiate in vitro into all three germ layers. Ongoing experiments aim at confirming these results also in vivo by generation of teratomas. In conclusion and in contrary to ERMS, fusion protein positive ARMS seem to follow the clonal evolution model in which each clone has tumorigenic potential. Moreover, PAX3-FOXO1 is the critical factor for ARMS self-renewal and a general inhibitor of differentiation.

Citation Format: Beat W. Schafer, Elisa Casanova, Sampoorna Satheesha, Melanie Müller, Paolo Cinelli, Paolo Cinelli. PAX3-FOXO1 increases fibroblast reprogramming efficiency and drives self-renewal in alveolar rhabdomyosarcoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3104. doi:10.1158/1538-7445.AM2014-3104

Mechanics of Flexible Needles Robotically Steered through Soft Tissue

The tip asymmetry of a bevel-tip needle results in the needle naturally bending when it is inserted into soft tissue. This enables robotic needle steering, which can be used in medical procedures to reach subsurface targets inaccessible by straight-line trajectories. However, accurate path planning and control of needle steering requires models of needle-tissue interaction. Previous kinematic models required empirical observations of each needle and tissue combination in order to fit model parameters. This study describes a mechanics-based model of robotic needle steering, which can be used to predict needle behavior and optimize system design based on fundamental mechanical and geometrical properties of the needle and tissue. We first present an analytical model for the loads developed at the tip, based on the geometry of the bevel edge and material properties of soft-tissue simulants (gels). We then present a mechanics-based model that calculates the deflection of a bevel-tipped needle inserted through a soft elastic medium. The model design is guided by microscopic observations of needle-gel interactions. The energy-based formulation incorporates tissue-specific parameters, and the geometry and material properties of the needle. Simulation results follow similar trends (deflection and radius of curvature) to those observed in experimental studies of robotic needle insertion.

Abstract C113: p21 downregulation is an important component of PAX3/FKHR oncogenicity and its reactivation by histone deacetylase inhibitors enhances combination treatment

A number of drugs developed against cancer-specific molecular targets have been shown to offer survival benefits alone or in combination with standard treatments, especially for those cases where tumor pathogenesis is dominated by a single molecular abnormality. One example for such a tumor type is alveolar rhabdomyosarcoma (aRMS) which is characterized by a specific translocation creating the oncogenic PAX3/FKHR transcription factor, believed to be the main molecular basis of the disease. Recently, we were able to demonstrate that the small molecule inhibitor PKC412 exhibits strong antitumor activity against aRMS by reducing the transcriptional activity of PAX3/FKHR.

In the present study, we screened for combination strategies that are superior to PKC412 treatment alone. Interestingly, we found that the combination of PKC412 with histone deacetylase (HDAC) inhibitors like valproic acid (VPA) synergistically induced apoptosis resulting in suppressed aRMS tumor growth in vivo.

We provide evidence that the enhanced antitumor effect upon combination treatment is achieved by VPA-induced reactivation of p21 which is downregulated in aRMS tumor cells via destabilization of its transcriptional regulator EGR1 by PAX3/FKHR. This identifies downregulation of p21 as a crucial event in PAX3/FKHR oncogenicity. Our study not only highlights a possible mechanism behind the increased efficacy of combination treatment but also indicates that different levels of PAX3/FKHR oncogenicity can be exploited therapeutically by a specific combination of anticancer drugs to increase their therapeutic potential.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C113.

Diminished expression of S100A2, a putative tumour suppressor, is an independent predictive factor of neck node relapse in laryngeal squamous cell carcinoma

PURPOSE

In primary squamous cell carcinoma of the larynx (LSCC), Ca(2+) binding S100A2 protein underexpression was already found to be associated with poor tumour differentiation and shorter overall survival. In the present work, the role of S100A2 protein expression in the prediction of regional metastasis-free survival (MFS) was investigated to guide neck management in LSCC.

EXPERIMENTAL DESIGN

Specimens of LSCC from 62 consecutive untreated patients were examined for S100A2 content by immunocytochemistry; the patients were followed up for a median of 44 months (range 2-90 months) after initial surgical resection. MFS was calculated from the date of first surgery to that of regional neck node recurrence.

RESULTS

S100A2 was detected in 18 of 19 (95%) low-grade tumours and in 22 of 43 (51%) high-grade tumours. The 5-year regional MFS was 81% for patients with S100A2-positive tumours and 55% for patients with S100A2-negative tumours. By multivariate analysis, the S100A2 status appeared to be a significant independent predictive factor for MFS (p = .02).

CONCLUSIONS

Our results suggest that the assessment of S100A2 status at diagnosis may identify a subset of LSCC patients highly susceptible to neck node metastases and may thus help define therapy accordingly.

Anemia and survival in childhood acute lymphoblastic leukemia

BACKGROUND

Several studies have demonstrated that patients with childhood acute lymphoblastic leukemia presenting with mild anemia at diagnosis have an increased risk of poor outcome compared to patients with more severe anemia. However, it has not been reported whether there is any correlation between degree of anemia and leukemia subtype.

DESIGN AND METHODS

In a cohort of 1162 patients with childhood acute lymphoblastic leukemia we analyzed whether there was a correlation between degree of anemia and leukemia subtype. We also studied the association between degree of anemia and event-free survival within the subtypes.

RESULTS

Hemoglobin levels at diagnosis were distributed in a non-random pattern. The degree of anemia was significantly different for three distinct groups of patients compared to the remaining patients (mean hemoglobin; T-cell leukemia: 106 g/L versus 76 g/L (precursor B-cell acute lymphoblastic leukemia); within precursor B-cell ALL: TEL-AML1 positive: 68 g/L versus 79 g/L; BCR-ABL positive: 93 g/L versus 76 g/L; each p<0.05). Furthermore, in contrast to the entire study group, patients with T-cell leukemia, TEL-AML1(+), and BCR-ABL(+) precursor B-cell leukemia had a more favorable prognosis if presenting with a higher hemoglobin level (>/=80 g/L).

CONCLUSIONS

These observations indicate that the formerly reported direct correlation between severity of anemia and survival in childhood acute lymphoblastic leukemia mainly reflects differences in the degree of anemia between distinct biological subgroups with different treatment outcomes. On the other hand, the inverse relationship between severity of anemia and survival found within specific subgroups suggests that very low hemoglobin levels at diagnosis are associated with more advanced disease in these subgroups.

Four and half lim protein 2 (FHL2) stimulates osteoblast differentiation

FHL2, a molecule that interacts with many integrins and transcription factors, was found to play an important role in osteoblast differentiation. Overexpression of FHL2 increases the accumulation of osteoblast differentiation markers and matrix mineralization, whereas FHL2 deficiency results in inhibition of osteoblast differentiation and decreased bone formation.

INTRODUCTION

Integrin-matrix interaction plays a critical role in osteoblast function. It has been shown that the cytoplasmic domains of integrin beta subunits mediate signal transduction induced by integrin-matrix interaction. We reasoned that the identification of proteins interacting with beta-cytoplasmic tails followed by analysis of the function of these proteins would enhance our understanding on integrin signaling and the roles of these proteins in osteoblast activities.

MATERIALS AND METHODS

Yeast two hybrid assay was used to identify proteins interacting with the cytoplasmic domain of integrin beta5 subunit. The association of these proteins with integrin alphavbeta5 was confirmed by confocal analysis and co-immunoprecipitation. A stable MC3T3-E1 cells line overexpressing Four and Half Lim Protein 2 (FHL2) and mouse osteoblasts deficient in FHL2 were used to study the roles of FHL2 in osteoblast differentiation and bone formation. Matrix protein expression was determined by mRNA analysis and Western blotting. Matrix mineralization was detected by Alizarin red staining. Alkaline phosphatase activity was also measured. muCT was used to determine bone histomorphometry.

RESULTS AND CONCLUSIONS

FHL2 and actin-binding proteins, palladin and filamin A, were identified as proteins interacting with beta5 cytoplasmic domain. FHL2 co-localized with alphavbeta5 at the focal adhesion sites in association with palladin and filamin A. FHL2 was also present in nuclei. Osteoblasts overexpressing FHL2 exhibited increased adhesion to and migration on matrix proteins. Conversely, FHL2 stimulation of CREB activity was dependent on integrin function because it was inhibited by Gly-Arg-Gly-Asp-Ser (GRGDS) peptide. The expression of osteoblast differentiation markers and Msx2 was upregulated, and bone matrix mineralization was increased in FHL2 overexpressing cells. In contrast, FHL2-deficient bone marrow cells and osteoblasts displayed decreased osteoblast colony formation and differentiation, respectively, compared with wildtype cells. Moreover, FHL2-deficient female mice exhibited greater bone loss than the wildtype littermates after ovariectomy. Thus, FHL2 plays an important role in osteoblast differentiation and bone formation.

Cancer predisposition in mice deficient for the metastasis-associated Mts1(S100A4) gene

Metastasis-promoting Mts1(S100A4) protein belongs to the S100 family of Ca(2+)-binding proteins. A mouse strain with a germ-line inactivation of the S100A4 gene was generated. The mice were viable and did not display developmental abnormalities in the postnatal period. However, an abnormal sex ratio was observed in the litters with the S100A4-/- genotype, raising the possibility of a certain level of embryonic lethality in this strain. In all, 10% of 10-14-month-old S100A4-null animals developed tumors. This is a characteristic feature of mouse strains with inactivated tumor suppressor genes. Spontaneous tumors of S100A4-/- mice were p53 positive. Recently, we have shown that S100A4 interacts with p53 tumor suppressor protein and induces apoptosis. We proposed that impairment of this interaction could affect the apoptosis-promoting function of p53 that is involved in its tumor suppressor activity. The frequency of apoptosis in the spleen of S100A4-/- animals after whole-body gamma-irradiation was reduced compared to the wild-type animals. The same was true for the transcriptional activation of the p53 target genes - waf/p21/cip1 and bax. Taken together, these observations indicate that spontaneous tumors in S100A4-/- mice are a result of functional destabilization of p53 tumor suppressor gene.

Telomerase activity in cell lines of pediatric soft tissue sarcomas

Telomeres and their maintenance by telomerase have been implicated to play an important role in carcinogenesis. As almost all malignant tumors express telomerase (in contrast to normal somatic cells), assessment of its activity has been proposed as a diagnostic and prognostic tool. To test the prognostic value of telomerase in pediatric soft tissue sarcoma (STS), we analyzed telomere length (by telomere restriction fragment analysis), telomerase activity (by modified telomerase repeat amplification protocol assay), and expression of human telomerase reverse transcriptase (hTERT) mRNA (by TaqMan technique) in cell lines of different types of STS from 12 children and adolescents. Telomere length (3.7-9.0 kb) showed a very heterogeneous pattern, independent of subtype of STS or the age of the patients, and it was not associated with expression of hTERT mRNA. In contrast, there was a trend of an association between hTERT and telomerase activity. The three tested cell lines of embryonal rhabdomyosarcomas demonstrated no or low (n = 2) telomerase activity, which was confirmed in two cases by a very low expression of hTERT mRNA. Thus, we suggest that the significant difference (p < 0.01) in the less aggressive clinical behavior of embryonal rhabdomyosarcomas in comparison to other subtypes may be due to differences in telomerase expression. Taken together, our cell line experiments imply that telomerase activity might be a biologic marker for stratification between STS with different clinical prognosis.

Inverse expression of S100A4 and E-cadherin is associated with metastatic potential in gastric cancer

S100A4 is known to be involved in cancer cell motility by virtue of its ability to activate nonmuscle myosin. E-cadherin has an important role in the homophilic cell-cell adhesion and is called an invasion suppressor gene. In the current study, we investigate the histological type and metastatic potential of gastric cancer from the aspect of the interrelationship of E-cadherin and S100A4 expression. Expression of E-cadherin and S100A4 in gastric cancer cell lines, primary gastric cancers, and their normal counterparts were analyzed by reverse transcription-PCR, Western blot, and immunohistochemical methods. S100A4 protein and E-cadherin were expressed in five of eight gastric cancer cell lines, and inverse expression of the two proteins are found in four cell lines. In the clinical specimens, E-cadherin mRNA expression in differentiated adenocarcinomas (88%, 14 of 16) was significantly more frequent than that in poorly differentiated adenocarcinomas (50%, 22 of 44; P = 0.015). Western blot analysis demonstrates that S100A4 protein expression in poorly differentiated adenocarcinomas was 1.6-fold higher than in well differentiated adenocarcinoma. Immunohistochemically, S100A4 expression was detected in 51 (55%) of 92 primary gastric cancers. Reduced expression of E-cadherin in primary tumors was found in 66 (72%) of 92 tumors. S100A4 expression in the poorly differentiated adenocarcinomas had a strong relation to positive lymph node involvement or peritoneal dissemination. Reduced E-cadherin expression showed a strong relationship with positive serosal involvement and infiltrating type. Tumors classified as a group with reduced E-cadherin and high expression of S100A4 reveal positive peritoneal dissemination, serosal involvement, and infiltrating type in the growth pattern. Furthermore, these tumors showed a strong correlation with the poorly differentiated adenocarcinoma. In contrast, tumors with preserved E-cadherin and low expression of S100A4 have a close relation to the well differentiated adenocarcinoma and a favorable prognosis. By the Cox proportional hazard model, S100A4 and E-cadherin tissue status was judged as an independent prognostic factor. S100A4 and E-cadherin tissue status may be a powerful aid in evaluating metastatic potential or the prognosis of patients with gastric cancer.

Concomitant amplification and expression of PAX7-FKHR and MYCN in a human rhabdomyosarcoma cell line carrying a cryptic t(1;13)(p36;q14)

Alveolar rhabdomyosarcoma (ARMS) is associated with the specific chromosomal translocation (2;13)(q35;q14) or its rarer variant t(1;13)(p36;q14), which produces the fusion gene PAX7-FKHR. Here we describe the human cell line RC2, derived from an ARMS, which harbors a cryptic t(1;13)(p36;q14) and concomitantly shows amplification of the PAX7-FKHR fusion gene and of the MYCN oncogene. The t(1;13) and MYCN oncogene were studied by standard cytogenetic analysis and molecular techniques. The reverse transcriptase polymerase chain reaction demonstrated the expression of PAX7-FKHR mRNA in RC2 cells, although karyotype analysis failed to demonstrate a t(1;13)(p36;q14) chromosomal translocation or a derivative 13 chromosome. Double minute chromosomes were detected in all the metaphases studied. Fluorescence in situ hybridization analysis revealed multiple copies of the PAX7-FKHR fusion gene localized exclusively on a subset of double minutes, whereas multiple copies of MYCN were identified on other double minute chromosomes. Southern-blot analysis demonstrated that RC2 cells contain approximately 20 copies of the MYCN oncogene. So far no continuous RMS cell line carrying the t(1;13)(p36;q14) has been described, and PAX7-FKHR and MYCN amplifications have always been reported to occur separately in rhabdomyosarcoma (RMS). The availability of an ARMS cell line that harbors the t(1;13)(p36;q14) constitutes a useful tool for further understanding the role of the PAX7-FKHR fusion gene in RMS oncogenesis and may improve knowledge of the possible relation between PAX7-FKHR and MYCN amplification.

Clinical significance of S100A4 and E-cadherin-related adhesion molecules in non-small cell lung cancer

S100A4 has been implicated in the malignant phenotype of tumor cells, including cell motility, but the biological function is hardly known. A recent study suggests that S100A4-induced invasiveness in malignant tumor cells is partially caused by down-regulation of E-cadherin. To clarify the clinical significance of S100A4 and its association with E-cadherin-mediated cell-to-cell adhesion system, we examined their protein expressions in non-small cell lung cancer (NSCLC) specimens using immunohistochemical techniques. Expression of S100A4 was observed in 81 (60%) of 135 NSCLCs and correlated with progression of the pathological T factor (p<0.001), lymph node metastasis (p<0.005), and poor survival (p<0.05). Reduced expression of E-cadherin, alpha-catenin, and beta-catenin was observed in 64% (87 of 135), 50% (43 of 86), and 58% (50 of 86) of the specimens tested, respectively. The expression of E-cadherin closely correlated with differentiation and inversely with that of S100A4. Among these adhesion-associated molecules we found that alpha-catenin appeared to reflect most strikingly the presence of lymph node metastasis and the short survival periods of NSCLC patients. Furthermore, patients who showed S100A4-positive/alpha-catenin-negative expression had a significantly shorter survival than the patients with S100A4-negative/alpha-catenin-positive expression. These results indicate that S100A4, as well as alpha-catenin, plays a role in the progression and metastasis of NSCLCs and that simultaneous immunohistochemical detection of their expression may be useful to define a subpopulation of lung cancer patients with a possible poor prognosis.

Photorhabdus luminescens W-14 insecticidal activity consists of at least two similar but distinct proteins. Purification and characterization of toxin A and toxin B

Both the bacterium Photorhabdus luminescens alone and its symbiotic Photorhabdus-nematode complex are known to be highly pathogenic to insects. The nature of the insecticidal activity of Photorhabdus bacteria was investigated for its potential application as an insect control agent. It was found that in the fermentation broth of P. luminescens strain W-14, at least two proteins, toxin A and toxin B, independently contributed to the oral insecticidal activity against Southern corn rootworm. Purified toxin A and toxin B exhibited single bands on native polyacrylamide gel electrophoresis and two peptides of 208 and 63 kDa on SDS-polyacrylamide gel electrophoresis. The native molecular weight of both the toxin A and toxin B was determined to be approximately 860 kDa, suggesting that they are tetrameric. NH2-terminal amino acid sequencing and Western analysis using monospecific antibodies to each toxin demonstrated that the two toxins were distinct but homologous. The oral potency (LD50) of toxin A and toxin B against Southern corn rootworm larvae was determined to be similar to that observed with highly potent Bt toxins against lepidopteran pests. In addition, it was found that the two peptides present in toxin B could be processed in vitro from a 281-kDa protoxin by endogenous P. luminescens proteases. Proteolytic processing was shown to enhance insecticidal activity.

Transcriptional activation of the human S100A2 promoter by wild-type p53

S100A2, a calcium binding protein of the EF-hand family, was recently identified to be inducible by etoposide, a p53 activator. A potential p53 binding site was identified in the promoter of the S100A2 gene, which binds to purified p53 as well as p53 in nuclear extract activated by etoposide. Transactivation assays using the promoter driven luciferase reporters revealed that the S100A2 promoter was transcriptionally activated by wild-type p53, but not by p53 mutants, in a dose-dependent as well as a p53 binding site-dependent manner. The p53-induced transactivation of the S100A2 promoter was enhanced by etoposide and blocked by a dominant negative p53 mutant. Furthermore, endogenous S100A2 mRNA expression is induced by etoposide in p53 positive, but not in p53 negative cells. Thus, p53 appears to positively regulate S100A2 expression.

Localization of Ca(2+)-binding S100 proteins in epithelial tumours of the skin

The Ca(2+)-binding proteins S100A1, S100A2, S100A4, S100A6 and S100B were evaluated immunohistochemically in normal skin and skin appendage tumours. Epidermal basal cells, epithelial cells of sebaceous glands, hair follicle sheet epithelia and eccrine duct reacted strongly with an antiserum against human S100A2 but were nonreactive or weakly reactive to S100A1, S100A4, S100A6 and S100B. Varying types of skin appendage tumours and most peripheral cells in tumour nests of basal cell carcinoma and squamous cell carcinoma showed positive S100A2 immunoreactivity in neoplastic cells corresponding to basal cells but were nonreactive or faintly reactive for other S100 proteins. Langerhan's cells and melanocytes were labelled by S100B. Basophilic cells of calcifying epithelioma were occasionally stained with S100A2 antiserum. Eccrine poroma did not react with any S100 antiserum. Mixed tumours of the skin containing neoplastic myoepithelial cells stained strongly for S100A2 and S100B but only faintly for S100A1, S100A4, S100A6. This is the first report on selective evaluation of different S100 proteins in normal skin. These antibodies are valuable tools for better characterization of skin appendage tumours.