Amplification and overexpression of the hepatocyte growth factor receptor (HGFR/MET) in rat DMBA sarcomas

In the present study subcutaneous fibrosarcomas were induced by the carcinogen 7,12-dimethylbenz(a)anthracene (DMBA) in rats from F1 generation cross breedings of two different inbred strains. Comparative genomic hybridization (CGH) analysis, which allows detection of DNA sequence copy changes, was applied to one of the tumors and it was found that there were increased copy numbers of sequences at chromosome 4q12-q21 in this tumor. We have previously determined that the loci for the hepatocyte growth factor (Hgf) and hepatocyte growth factor receptor (Hgfr/Met), a protooncogene, are situated in this particular chromosome region. Using probes for the two genes in FISH (fluorescence in situ hybridization) and in Southern blots we found that the Hgfr/Met gene was amplified in five of the 19 sarcomas studied, and that the Hgf gene was coamplified in two of them. Northern and Western blots and tyrosine phosphorylation analysis showed that the HGF receptor was overexpressed and functional in all five tumors, as well as in two additional tumors. In summary, both amplification and overexpression of the Hgfr/Met gene was found in about 25% of DMBA-induced experimental rat sarcomas, and HGF receptor overexpression alone was seen in two additional tumors. Possibly this reflects an involvement in paracrine or autocrine stimulation of growth and invasiveness by HGF. Our finding could provide a rodent model system to increased knowledge about causality and therapy, which may be applicable to the sizeable fraction of human musculoskeletal tumors displaying MET overexpression.

LHFP, a novel translocation partner gene of HMGIC in a lipoma, is a member of a new family of LHFP-like genes

A major cytogenetic subgroup among human lipomas is characterized by translocations involving the HMGIC gene at 12q15. In the context of an ongoing research program aiming at the elucidation of the functional consequences of HMGIC translocations in the etiology of lipomas, we have isolated a novel human gene, LHFP (lipoma HMGIC fusion partner), that acts as a translocation partner of HMGIC in a lipoma with t(12;13). The LHFP gene was mapped to the long arm of chromosome 13, a region recurrently targeted by chromosomal aberrations in lipomas. By Northern blot analysis, a transcript of 2. 4 kb was detected in a variety of human tissues. We assembled a cDNA contig containing the entire coding region of LHFP. Nucleotide sequence analysis of the composite LHFP cDNA revealed an open reading frame encoding a protein of 200 amino acids. The predicted human LHFP protein is almost identical to a translated mouse EST that covers almost the entire LHFP coding region. In addition, BLAST searches revealed that the LHFP protein belongs to a new protein family consisting of at least four or five members. In the lipoma studied, the expressed HMGIC/LHFP fusion transcript encodes the three DNA binding domains of HMGIC followed by 69 amino acids encoded by frame-shifted LHFP sequences. LHFP is the second translocation partner of HMGIC identified in lipomas and represents a candidate target gene for lipomas with 13q aberrations.

The structure and dynamics of ring chromosomes in human neoplastic and non-neoplastic cells

Acquired ring chromosomes have been found in most types of human neoplasia, with a frequency approaching 10% in malignant mesenchymal tumours. In this study, the composition and dynamics of ring chromosomes were analysed in eight cases of acute myelogenous leukaemia, 17 solid tumours, and five cases with constitutional rings. Chromosomal banding and fluorescence in situ hybridisation were performed to determine the content and the structural heterogeneity of the rings. Telomeric repeats were detected using peptide nucleic acid probes or primed in situ labelling, whereas centromeric activity was evaluated by detection of kinetochore proteins. Mitotic instability was assessed by the frequency of anaphase bridges. The results suggest that human ring chromosomes can be structurally and functionally divided into two categories. In the first of these, size variation is minimal and rearrangement at cell division is uncommon. The majority of such rings contain subtelomeric sequences. Constitutional ring chromosomes and most rings in leukaemias belong to this group, whereas only a few mesenchymal tumours exhibit rings of this type. The second category consists of rings with amplified sequences, primarily from chromosome 12, characteristically occurring in atypical lipomatous tumours and other subtypes of low or borderline malignant mesenchymal neoplasms. Variation in size and number is extensive, and breakage-fusion-bridge events occur at a high frequency. Abnormalities in pericentromeric sequences are common and, in some cases, kinetochores assemble in the absence of alphoid DNA. We conclude that it is not only the ring structure per se or the neoplastic nature of the host cell that determines ring instability, but probably also the functional role of the genes carried in the ring.

Rearrangement of the neoplasia-associated gene HMGIC in synovia from patients with osteoarthritis

The occurrence of clonal chromosome aberrations in short-term cultures from synovia, osteophytes, and cartilage from patients with osteoarthritis (OA) was recently reported. Among these aberrations, a recurrent involvement of chromosome bands 12q13-15 in structural rearrangements was detected in both synovia and osteophytes. Chromosomal abnormalities of 12q13-15 are frequent among malignant and benign mesenchymal tumors, and it was recently demonstrated that the molecular target in these neoplasms is the HMGIC gene. In this study, we show by fluorescence in situ hybridization that HMGIC was disrupted by rearrangements of 12q15 in synovia from two patients with OA. The finding of HMGIC rearrangement in a lesion that is not traditionally regarded as neoplastic not only widens the spectrum of disorders that may be associated with altered function of this gene, but also provides further support for the notion that genetically rearranged cell populations are part of the OA process.

Conserved mechanism of PLAG1 activation in salivary gland tumors with and without chromosome 8q12 abnormalities: identification of SII as a new fusion partner gene

We have previously shown (K. Kas et al, Nat. Genet., 15: 170-174, 1997) that the developmentally regulated zinc finger gene pleomorphic adenoma gene 1 (PLAG1) is the target gene in 8q12 in pleomorphic adenomas of the salivary glands with t(3;8)(p21;q12) translocations. The t(3;8) results in promoter swapping between PLAG1 and the constitutively expressed gene for beta-catenin (CTNNB1), leading to activation of PLAG1 expression and reduced expression of CTNNB1. Here we have studied the expression of PLAG1 by Northern blot analysis in 47 primary benign and malignant human tumors with or without cytogenetic abnormalities of 8q12. Overexpression of PLAG1 was found in 23 tumors (49%). Thirteen of 17 pleomorphic adenomas with a normal karyotype and 5 of 10 with 12q13-15 abnormalities overexpressed PLAG1, which demonstrates that PLAG1 activation is a frequent event in adenomas irrespective of karyotype. In contrast, PLAG1 was overexpressed in only 2 of 11 malignant salivary gland tumors analyzed, which suggests that, at least in salivary gland tumors, PLAG1 activation preferentially occurs in benign tumors. PLAG1 over-expression was also found in three of nine mesenchymal tumors, i.e., in two uterine leiomyomas and one leiomyosarcoma. RNase protection, rapid amplification of 5'-cDNA ends (5'-RACE), and reverse transcription-PCR analyses of five adenomas with a normal karyotype revealed fusion transcripts in three tumors. Nucleotide sequence analysis of these showed that they contained fusions between PLAG1 and CTNNB1 (one case) or PLAG1 and a novel fusion partner gene, i.e., the gene encoding the transcription elongation factor SII (two cases). The fusions occurred in the 5' noncoding region of PLAG1, leading to exchange of regulatory control elements and, as a consequence, activation of PLAG1 gene expression. Because all of the cases had grossly normal karyotypes, the rearrangements must result from cryptic rearrangements. The results suggest that in addition to chromosomal translocations and cryptic rearrangements, PLAG1 may also be activated by mutations or indirect mechanisms. Our findings establish a conserved mechanism of PLAG1 activation in salivary gland tumors with and without 8q12 aberrations, which indicates that such activation is a frequent event in these tumors.

Cytogenetic aberrations in Ewing sarcoma: are secondary changes associated with clinical outcome?

BACKGROUND

Ewing sarcoma is associated with a nonrandom pattern of primary and secondary chromosomal aberrations. Whereas the finding of rearrangements of chromosome 22, usually in the form of a balanced translocation t(11;22)(q24;q12), is important diagnostically, nothing is known about the potential prognostic impact of the secondary chromosomal aberrations.

PROCEDURE

During a 1 3-year-period, short-term cultured tumor samples from 21 children and young adults with Ewing sarcoma were cytogenetically analyzed successfully.

RESULTS

Clonal chromosome aberrations were detected in 18 patients, 17 of whom had the characteristic t(11;22)(q24;q12) or variants thereof. The most frequent secondary change was +8, followed by +12, +2, +5, +9, +15, and gain of material from the long and short arms of chromosome 1. The only recurrent secondary change that was restricted to tumors from the ten patients that were dead at latest follow-up was gain of 1q material. Furthermore, all three patients with tumors with chromosome numbers over 50 had died, and the only patient with a tumor karyotype lacking chromosome 22 rearrangement was alive without evidence of disease.

CONCLUSIONS

These data and previously published results indicate that the karyotypic pattern not only may be of diagnostic significance but also may be important prognostically.

Amplification of 12q13 and 12q15 sequences in a sclerosing epithelioid fibrosarcoma

Sclerosing epithelioid fibrosarcoma (SEF) is a recently described entity. It is a low-grade sarcoma that occurs primarily in the deep soft tissues of the extremities of adults. It may histologically simulate benign lesions such as fibroma and myxoma or malignancies such as sclerosing carcinoma and lymphoma, extraskeletal myxoid chondrosarcoma, clear cell sarcoma of tendons and aponeuroses, and synovial sarcoma, depending on the lesion's cellularity, degree of fibrosis, and amount of myxoid matrix. There are no previously published cytogenetic studies of this tumor. We found the karyotype 40-45,XY,add(9)(p13),add(10)(p11),-12,-13,-18,add(18)(q11),add(20)(q11) in a SEF of a 14-year-old boy, by using chromosome banding. Fluorescence in situ hybridization showed that both the add(10) and the add(18) contained amplified sequences from 12q13 and 12q15, including the HMGIC gene. Chromosome 18 material was present in the add(9) and terminally in the add(10). The karyotype of this case indicates that SEF is unrelated to extraskeletal myxoid chondrosarcoma, clear cell sarcoma, and synovial sarcoma. When compared with the findings in other soft tissue tumors such as well-differentiated liposarcoma and low-grade malignant fibrous histiocytoma, the chromosome banding and in situ hybridization data add support to the notion that SEF is a relatively low grade variant of fibrosarcoma.

A case of dermatofibrosarcoma protuberans with a ring chromosome 5 and a rearranged chromosome 22 containing amplified COL1A1 and PDGFB sequences

Dermatofibrosarcoma protuberans (DFSP) is a cutaneous tumour of borderline malignancy, the cytogenetic features of which include the translocation t(17;22)(q22;q13) or, more commonly, supernumerary ring chromosomes containing material from 17q22 and 22q13. These rearrangements result in the COL1A1/PDGFB fusion gene. Here, we describe a case of DFSP displaying a ring chromosome 5 together with a large marker chromosome composed of chromosome 22 alphoid DNA, material from distal 12q and amplified COL1A1 and PDGFB sequences. This is the first case of DFSP with multiple copies of COL1A1 and PDGFB not confined to ring chromosomes, showing that DFSP is similar to other borderline malignant mesenchymal tumours, where rings and giant markers are alternative vehicles for amplified material.

Chromosomal organization of amplified chromosome 12 sequences in mesenchymal tumors detected by fluorescence in situ hybridization

The chromosomal organization of amplified chromosome 12 sequences was studied with fluorescence in situ hybridization in six mesenchymal tumors: two osteosarcomas, one lipoma, two liposarcomas, and one fibrosarcoma. All except the fibrosarcoma contained ring and/or giant marker chromosomes. Amplification of chromosome 12 sequences, demonstrated with whole-chromosome paint in all cases, was confined to ring and giant marker chromosomes in four tumors. In one of the osteosarcomas and in the fibrosarcoma, amplified sequences were added to chromosome 12 and to chromosomes 10, 12, 18, and the Y chromosome, respectively. Hybridizations with single-copy probes demonstrated considerable inter- and intracellular variation in the arrangement of chromosome 12 sequences in ring and marker chromosomes. Amplification of 12q13-15 sequences, predominantly from the HMGIC-MDM2 region, was detected in all cases, but the two osteosarcomas also contained amplification of 12p material. This finding, combined with results from previous studies, indicates that 12p amplification is a feature distinguishing osteosarcomas from adipose tissue tumors. A novel finding was the presence of positive signals for chromosome 12 alpha-satellite sequences in ring and marker chromosomes in four cases. Rod chromosomes carrying amplified material, in particular those that were relatively stable, frequently exhibited chromosome 12 negative terminal segments; two of these, present in two separate cases, were shown by C-banding to contain constitutive heterochromatin. The significant intercellular heterogeneity in the number and structure of rings and giant markers in a subset of mesenchymal tumors could be explained by continuous recombination through breakage-fusion-bridge cycles. If so, this process will continue until broken ends become stabilized, for example by acquisition of telomeric segments from other chromosomes.

Cytogenetics of uterine sarcomas: presentation of eight new cases and review of the literature

Tissue from 14 uterine tumor samples from eight patients-four with endometrial stromal sarcoma (ESS), two with leiomyosarcoma (ULMS), and two with malignant mixed mesodermal tumor (MMMT)-were investigated cytogenetically after short-term culturing. Clonal chromosome aberrations were found in 12 tumors. One ESS showed a recombination between 7p14 and 17q12, a rearrangement characterizing a subset of ESSs. In our series, chromosomes 1, 6, 7, and 16 were involved in structural aberrations most frequently (four cases each). Net loss of 6q material was found in four cases and bands 11q13, 16q13, and 22q13 were each rearranged in four cases. Among 43 uterine sarcomas, including 12 MMTs, now available for evaluation, some differences in breakpoint distribution among different tumor types were found. Rearrangements of bands 1p32, 3p24, and 10q22 were found exclusively in ULMS, whereas aberrations of bands 6p21, 7p21, and 17q12 were found predominantly in ESS.

Various regions within the alpha-helical domain of the COL1A1 gene are fused to the second exon of the PDGFB gene in dermatofibrosarcomas and giant-cell fibroblastomas

Dermatofibrosarcoma protuberans (DFSP) and its juvenile form, giant-cell fibroblastoma (GCF), are uncommon infiltrative tumors of the dermis, which present unique cytogenetic features, such as the reciprocal translocation t(17;22) or, more commonly, supernumerary ring chromosomes containing sequences from chromosomes 17 and 22. We have recently shown that these aberrations are cytogenetic manifestations of gene fusions between the platelet-derived growth factor B-chain gene (PDGFB), the cellular equivalent of the v-sis oncogene, and the collagen type 1 alpha 1 gene (COL1A1), the major protein constituent of the extracellular matrix in connective tissue of skin. We now report characterization of COL1A1/PDGFB chimeric genes at the RNA and DNA sequence levels in a series of DFSPs and GCFs. All 16 tumors studied contained the COL1A1/PDGFB gene. The location of breakpoints within COL1A1 varied greatly, but was always limited to the region encoding the alpha-helical domain. The PDGFB segment of the chimeric transcript always starts with exon 2, placing PDGFB under the control of the COL1A1 promoter and removing all known elements negatively controlling PDGFB transcription and translation. Production of these aberrant transcripts in fibroblasts, the suspected cell of origin of DFSP/GCF, likely causes autocrine stimulation and cell proliferation. No specific function has yet been assigned to exon 2 of PDGFB, and this exon does not encode for the mature growth factor. Its retention in all chimeric COL1A1/PDGFB genes suggests that it is important for the normal processing of the PDGFB polypeptide.

Complex karyotype in a childhood adrenocortical carcinoma

Cytogenetic analysis of short-term cultured cells from an 11-cm adrenocortical carcinoma in a 3.5-year-old girl revealed the karyotype 46,XX,inv(9)(p11q12)c/[2]/56-57,XX,+2,+4,+5,+7,+8,inv(9)c,+10,+add (13)(p11), +14,+15,+19,+20,+20,+mar[cp19]. To our knowledge, this is the first description of an abnormal karyotype in a pediatric adrenocortical tumor. Inasmuch as the distinction between benign and malignant adrenocortical tumors is often difficult to make from clinical and histopathologic data alone, the present findings suggest that cytogenetic analysis may be a valuable adjunct in the differential diagnosis.

Chromosome abnormalities in squamous cell carcinoma of the urethra

Cytogenetic analysis of short-term cultured cells from a urethral squamous cell carcinoma showed the tumor to have an abnormal, karyotypically complex near-diploid clone as well as its near-tetraploid duplicate. This is the first urethral carcinoma with chromosomal abnormalities to be reported. Chromosomes Y, 2, 3, 4, 6, 7, 8, 11, and 20 were all involved in numerical and/or structural rearrangements. Of particular interest was the fact that no rearrangements of chromosomes 9 and 17, both almost ubiquitously involved in transitional cell carcinoma of the urinary tract, were seen.

Cytogenetic heterogeneity in a second primary radiation-induced bladder carcinoma: ten karyotypically unrelated clones

Cytogenetic analysis of a transitional cell carcinoma (TCC) of the bladder, the tumor having developed 32 years after the patient received pelvic irradiation and interstitial radium implantation for an endometrial carcinoma, revealed the presence of 10 cytogenetically abnormal, unrelated clones. Although the tumor was poorly differentiated, all clones were pseudo- or near-diploid with rather simple balanced or unbalanced structural rearrangements or both. The chromosomes involved in structural changes more than once were chromosomes 8, 9, and 11, which were rearranged in three clones, and chromosomes 3 and 17, both rearranged in two clones. No previous TCC of the bladder with cytogenetically unrelated clones has been reported, nor has any such radiation-induced tumor with chromosomal abnormalities been described. The distinct karyotypic and clonal pattern of the case presented here is probably indicative of a carcinogenic field effect due to the previous pelvic irradiation. Postradiation bladder carcinomas thus seem to be distinct cytogenetically in addition to their known unique etiological and clinical features.

FISH characterization of head and neck carcinomas reveals that amplification of band 11q13 is associated with deletion of distal 11q

In order to characterize homogeneously staining regions (HSR) and other 11q13 rearrangements identified cytogenetically, we performed fluorescence in situ hybridization (FISH) using a CCND1 cosmid and five YAC clones spanning chromosomal bands 11q13-14 on metaphase cells from 14 primary and one metastatic head and neck carcinomas. At the cytogenetic level, a total of 17 HSR were detected in ten cases: five were in derivative chromosomes 11 in band 11q13, and 12 were located in other derivative chromosomes. Other forms of 11q13 rearrangements were observed in five cases, whereas two cases had normal chromosomes 11. FISH analysis demonstrated that all HSR but two were derived from the 11q13 band. The size of the amplicon varied from case to case, but the amplification always included the region covered by YAC 55G7, which contains the CCND1 locus. The amplification of CCND1 was confirmed by use of a CCND1 cosmid. We also showed that most of the cases (9 of 11) with 11q13 amplification had lost material from distal 11q. The breakpoints were mapped by FISH and were shown to cluster to the region between YACs 55G7 and 749G2. We conclude that loss of gene(s) in distal 11q may be as important as amplification of genes in 11q13 for the biological aggressiveness of head and neck carcinomas.

Cytogenetic and molecular genetic demonstration of polyclonality in an acinic cell carcinoma

The paradigm that human malignancies are monoclonal has been questioned during recent years by the finding of unrelated, cytogenetically aberrant clones in short-term cultures from certain tumour types, notably carcinomas of the breast, skin and upper aerodigestive tract. In order to analyse whether cytogenetically unrelated clones are also unrelated at the molecular level, we analysed the X-chromosome inactivation status in cell cultures from a cytogenetically highly polyclonal acinic cell carcinoma of the parotid gland. By using cell cultures dominated by a single abnormal clone, obtained through in vitro culturing for 3-5 passages, we showed that the different clones must indeed have originated from different cells.

Inflammatory leiomyosarcoma may be characterized by specific near-haploid chromosome changes

Identical near-haploid karyotypes with 28, X, +5, +18, +20, +21, +22 were found in two cases of inflammatory leiomyosarcoma, one of which had been reported previously as malignant fibrous histiocytoma. This abnormality may identify these tumours as a separate entity within this group of sarcomas.

Cytogenetic analysis of 46 pleomorphic soft tissue sarcomas and correlation with morphologic and clinical features: a report of the CHAMP Study Group. Chromosomes and MorPhology

With the aim of identifying objective cytogenetic-morphologic correlations, we evaluated 46 pleomorphic soft tissue sarcomas (mainly diagnosed originally as malignant fibrous histiocytomas) with clonal chromosome aberrations both cytogenetically and morphologically as part of an international collaborative study. By detailed histopathologic examination, most cases could be categorized into specific tumor types. Eight sarcomas were diagnosed as lipogenic (4 pleomorphic, 1 combined pleomorphic and myxoid/round cell, and 3 dedifferentiated liposarcomas), 19 as myogenic [11 leiomyosarcomas, 1 rhabdomyosarcoma, 4 myosarcomas not otherwise specified (NOS), and 3 probable myosarcomas NOS], 8 as myxofibrosarcomas, 1 as a malignant peripheral nerve sheath tumor, 1 as malignant mesenchymoma, 1 as extraskeletal osteosarcoma, I as sarcoma resembling proliferative fasciitis, and 7 as pleomorphic sarcomas NOS. In a three-grade system, 10 tumors were grade 2 and 36 were grade 3. The majority had highly complex karyotypes. A total of 24 recurrent abnormalities (defined by their presence in at least five cases) were detected: ring chromosomes, homogeneously staining regions (hsr) and/or double minute chromosomes (dmin), and structural rearrangement of 22 different chromosome bands or regions. The frequency and distribution of the recurrent karyotypic features were uneven. Grade 3 tumors displayed, on average, more aberrations per case than did grade 2 tumors. Nine of the selected abnormalities, including hsr/dmin and rearrangements of 19p13 and 19q13, were found only among the high-grade tumors. When the tumors were subdivided according to lineage of differentiation, the highest frequency of aberrations was seen in pleomorphic sarcomas NOS, followed by myxofibrosarcomas, myogenic sarcomas, and lipogenic sarcomas. None of the selected rearrangements was, however, specific for any of these subgroups. The sole consistent cytogenetic-morphologic association was that all three dedifferentiated liposarcomas had multiple abnormal clones, at least one of which contained supernumerary ring chromosomes. Due mainly to karyotype complexity, it therefore seems unlikely that cytogenetic analysis can assist in the differential diagnostic subclassification of pleomorphic sarcomas, nor was there any clear-cut indication that the karyotypic picture could be used to predict clinical outcome. Although the mean number of recurrent chromosome aberrations was almost twice as high in sarcomas that gave rise to metastases as among those that did not, no particular aberration was restricted to either of the two subgroups.

Nonrandom pattern of telomeric associations in atypical lipomatous tumors with ring and giant marker chromosomes

Atypical lipomatous tumors (ALTs) are cytogenetically characterized by supernumerary ring and giant marker chromosomes. Another common finding in ALT is that the tumor cells are cytogenetically heterogeneous with a variety of mostly nonclonal numerical and structural chromosome aberrations, including telomeric associations. In a series of 48 cytogenetically investigated ALTs, all chromosomal aberrations, clonal as well as nonclonal, were registered. Clonal ring chromosomes were present in 47 cases and giant markers in 11 cases. In 7 cases, 12 clonal telomeric associations were found and 37 cases showed nonclonal associations involving 344 identified telomeres. The telomere associations were nonrandomly distributed, with the telomeres of 11p, 20p, 20q, 9q, 15p, 19q, and 22q being most frequently (8.7-4.1% of all associations) involved; only Xp and Xq were never affected. The pattern of telomeric associations in ALT was compared with literature data on 47 giant cell tumors (880 telomeres), previously reported to show a nonrandom distribution of associations, and 36 sporadic cases of a variety of other human neoplasms (583 telomeres). The analysis indicated that the telomeres of 11p, 19q, and 20q are preferentially involved in associations in several tumor types. Among other structural aberrations in the ALT series, 221 nonclonal and 52 clonal breakpoints were identified, as well as 342 nonclonal and 14 clonal numerical aberrations. The combined data suggest that telomeric associations may predispose to acquired chromosome aberrations in neoplasia.

Nonrandom numerical chromosome abnormalities in basal cell carcinomas

Clonal chromosome abnormalities were found in 22 of 23 short-term cultured basal cell carcinomas (BCC) of the skin. The karyotypic abnormalities were nonrandom and in several cases included evidence of clonal evolution. Especially in cultures showing an epithelial growth pattern, simple numerical changes, most commonly +18, +9, +20, +7, and +5, predominated and presumably constitute pathogenetically important aberrations present in the neoplastic parenchyma. Also, several structural rearrangements of chromosome arm 9q were seen, which may be of particular interest against the background that a gene for familial BCC (Gorlin syndrome), the PTCH gene, maps to this region. Finally, most of the clonal aberrations detected in predominantly fibroblast-like cultures are likely to reflect changes acquired by cells of the tumor stroma, which raises the question whether mutations also of this tumor component may play a pathogenetic role in BCC development.