Nonrandom numerical chromosome abnormalities in basal cell carcinomas

Cytogenetic alterations in nonmelanoma skin cancer: a review

Since the advent of cytogenetic analysis, knowledge about fundamental aspects of cancer biology has increased, allowing the processes of cancer development and progression to be more fully understood and appreciated. Classical cytogenetic analysis of solid tumors had been considered difficult, but new advances in culturing techniques and the addition of new cytogenetic technologies have enabled a more comprehensive analysis of chromosomal aberrations associated with solid tumors. Our purpose in this review is to discuss the cytogenetic findings on a number of nonmelanoma skin cancers, including squamous- and basal cell carcinomas, keratoacanthoma, squamous cell carcinoma in situ (Bowen's disease), and solar keratosis. Through classical cytogenetic techniques, as well as fluorescence-based techniques such as fluorescence in situ hybridization and comparative genomic hybridization, numerous chromosomal alterations have been identified. These aberrations may aid in further defining the stages and classifications of nonmelanoma skin cancer and also may implicate chromosomal regions involved in progression and metastatic potential. This information, along with the development of newer technologies (including laser capture microdissection and comparative genomic hybridization arrays) that allow for more refined analysis, will continue to increase our knowledge about the role of chromosomal events at all stages of cancer development and progression and, more specifically, about how they are associated with nonmelanoma skin cancer.

Repetitive DNA alterations in human skin cancers

Repetitive sequences constitute landmarks for genome regulation, evolution, and chromatin architecture. Patterns of specific and non-specific repetitive sequences change in many types and stages of tumor cells, characterized by band loss, gain, and (de) increased staining of pre-existing bands. In this work, repetitive DNA was studied in search of genome instability of skin cancers: basal and squamous cell carcinomas (BCC and SCC), malignant melanoma (MM), melanocytic nevus (MN), and actinic keratosis (AK) lesions. DNAs were extracted from blood and tumor samples from 21 BCC, 7 SCC, 11 MM and 7 lesions. Banding patterns were obtained by random amplification of polymorphic DNA (RAPD), and specific D9S50 and D9S52 microsatellites (9p21). D9S50 patterns revealed microsatellite instability (MSI) and/or loss of heterozygosity (LOH) in 36% BCC, 25% SCC, and 57% MM tumors. D9S52 microsatellite showed 28.5%; 42.8%; and 71.4% altered tumors, respectively. No microsatellite alterations were found in MN and AK. On the other hand, genomic rearrangements detected by RAPD were present in 100% tumors. In BCC, the mean number of tumor DNA alterations showed predominant gain of bands. On the contrary, MM samples presented loss, or decreased intensity signal of RAPD bands. Genome alterations in skin cancers would result from chromosomal rearrangements, aneuploidy and/or polysomies. The low-cost and quick RAPD technique may reveal unknown genes or DNA sequences associated with tumor development and progression, and may be easily implemented in clinical diagnosis.

A specific chromosome aberration in a keratoacanthoma

Specific cytogenetic changes observed in various tumors indicate that a chromosomal event may play a key role in malignant transformation. We present a patient with keratoacanthoma with a sole chromosome abnormality. The karyotype found in short-term culture was 46,XY,t(2;8)(p13;p23); a normal male chromosome complement was also found. The finding of t(2;8) as a sole anomaly suggests that this aberration is a primary change in keratoacanthoma and might be important in the pathobiology of this tumor.

Clonal chromosome abnormalities in premalignant lesions of the skin

Two lesions, actinic keratosis (AK) and squamous cell carcinoma in situ (CIS), are believed to be precursors of squamous cell carcinoma (SCC) of the skin. These lesions can serve as an excellent model system for studying genetic changes associated with the inception of skin SCC. In the present study, five such lesions of the skin, three AKs and two AK+CIS, from three patients were short-term cultured and analyzed cytogenetically. One of the patients (case 3) had also an SCC in addition to three premalignant lesions. All lesions, but one, showed clonal karyotypic abnormalities. The recurrent changes identified were numerical, that is, +7 and +20. The structural rearrangements found in three AK were different, but it could be noted that the distal part of the long arm of chromosome 4 was involved in two AK and the SCC of case 3A. It was also interesting that chromosome 1 participated in structural rearrangements in three AK with band 1p31 being involved in two tumors. The karyotypic profile of these lesions is compared with that of skin SCC; it turns out that the general patterns are different in the sense that the SCC more often have complex karyotypes and display unbalanced aberrations involving the centromeric regions. Some karyotypic similarities between the SCC and their precursors are revealed. The fact that the structural rearrangements involving chromosomal band 3p13 and the centromeric region of chromosome 3 in AK are common features for many types of malignant tumors, including skin SCC, indicates that these changes are early genetic events associated with malignant transformation.

Specific aneusomies in Chinese hamster cells at different stages of neoplastic transformation, initiated by nitrosomethylurea

Aneuploidy is ubiquitous in cancer, and its phenotypes are inevitably dominant and abnormal. In view of these facts we recently proposed that aneuploidy is sufficient for carcinogenesis generating cancer-specific aneusomies via a chain reaction of autocatalytic aneuploidizations. According to this hypothesis a carcinogen initiates carcinogenesis via a random aneuploidy. Aneuploidy then generates transformation stage-specific aneusomies and further random aneusomies autocatalytically, because it renders chromosome segregation and repair mechanisms error-prone. The hypothesis predicts that several specific aneusomies can cause the same cancers, because several chromosomes also cooperate in normal differentiation. Here we describe experiments on the Chinese hamster (CH) that confirm this hypothesis. (i) Random aneuploidy was detected before transformation in up to 90% of CH embryo cells treated with the carcinogen nitrosomethylurea (NMU). (ii) Several specific aneusomies were found in 70-100% of the aneuploid cells from colonies transformed with NMU in vitro and from tumors generated by NMU-transformed cells in syngeneic animals. Among the aneuploid in vitro transformed cells, 79% were trisomic for chromosome 3, and 59% were monosomic for chromosome 10, compared with 8% expected for random distribution of any aneusomy among the 12 CH chromosomes. Moreover, 52% shared both trisomy 3 and monosomy 10 compared with 0.6% expected for random distribution of any two aneusomies. Among the tumor cells, 65% were trisomic for chromosome 3, 51% were trisomic for chromosome 5, and 30% shared both trisomies. Aneuploid cells without these specific aneusomies may contain minor transformation-specific aneusomies or may be untransformed. (iii) Random aneusomies and structurally altered chromosomes increased with the generations of transformed cells to the point where their origins became unidentifiable in tumors. We conclude that specific aneusomies are necessary for carcinogenesis.

Nonrandom karyotypic features in basal cell carcinomas of the skin

Cytogenetic analysis of short-term cultured 44 basal cell carcinomas (BCC) revealed clonal karyotypic abnormalities in 38 tumors. Relatively complex karyotypes (at least four structural and/or numerical changes per clone) with unbalanced structural as well as numerical aberrations were found in eight (approximately 21%) of the BCC, while the remaining BCC (79%) had simple karyotypes (1 to 3 aberrations per clone). Numerical changes only were found in 16 tumors, 15 BCC displayed both numerical and structural aberrations, and the remaining 7 BCC showed only structural aberrations. Extensive intratumoral heterogeneity, in the form of cytogenetically unrelated clones, was found in 21 tumors, whereas related subclones were present in 10 tumors. In order to obtain an overall karyotypic picture in BCC, the findings of our previously published 25 BCC have been reviewed. Our combined data indicate that BCC are characterized by nonrandom karyotypic patterns. A large subset of BCC is characterized by nonrandom numerical changes, notably, +18, +X, +7, and +9. Structural rearrangements often affect chromosomes 1, 4, 2, 3, 9, 7, 16, and 17. A number of chromosomal bands are frequently involved, including 9q22, 1p32, 1p22, 1q11, 1q21, 2q11, 4q21, 4q31, 1p36, 2q37, 3q13, 7q11, 11p15, 16p13, 16q24, 17q21, and 20q13. When the genomic imbalance is assessed, it has been shown that several chromosome segments are repeatedly involved in losses, namely loss of the distal part of 6q, 13q, 4q, 1q, 8q, and 9p. A correlation analysis between the karyotypic patterns and the clinico-histopathologic parameters has been undertaken in the 44 BCC of the present series. The cytogenetic patterns show a significant correlation with tumor status (P=.025), that is, that cytogenetically more complex tumors are also those clinically the most aggressive. Also, the frequency of cytogenetically unrelated clones is significantly higher in recurrent BCC than that in primary lesions (P=.05). No clear-cut association has been found between the karyotypic patterns and histologic subtypes or tumor sites.

Molecular cytogenetic analysis of basal cell carcinoma DNA using comparative genomic hybridization

In an attempt to define genomic copy number changes associated with the development of basal cell carcinoma, we investigated 15 sporadic tumors by comparative genomic hybridization. With the incorporation of tissue microdissection and degenerate oligonucleotide primed-polymerase chain reaction we were able to isolate, and then universally amplify, DNA from the tumor type. This combined approach allows the investigation of chromosomal imbalances within a histologically distinct region of tissue. Using comparative genomic hybridization we have observed novel and recurrent chromosomal gains at 6p (47%), 6q (20%), 9p (20%), 7 (13%), and X (13%). In addition comparative genomic hybridization revealed regional loss on 9q in 33% of tested tumors encompassing 9q22.3 to which the putative tumor suppressor gene, Patched, has been mapped. The deletion of Patched has been indicated in the development of hereditary and sporadic basal cell carcinomas. The identification of these recurrent genetic aberrations suggests that basal cell carcinomas may not be as genetically stable as previously thought. Further investigation of these regions may lead to the identification of other genes responsible for basal cell carcinoma formation.

Cytogenetic and interphase FISH analyses of 73 basal cell and three squamous cell carcinomas: different findings in direct preparations and short-term cell cultures

Cytogenetic analysis performed on 73 sporadic basal cell carcinomas (BCCs) and three squamous cell carcinomas (SCCs) showed different findings in direct preparations (24 hours) and in short-term cell cultures. Except for loss of the Y chromosome, not one of the other clonal (+6, +16, add(2)(q37), del(3)(q13), add(1)(p31), and near triploidy) or sporadic changes found in direct preparations was found in cell cultures and vice versa. Clonal trisomy 6 found in two BCC direct preparations and demonstrated by interphase fluorescence in situ hybridization in 8 other cases seems to be a nonrandom change in basal cell carcinoma. Immunohistochemistry showed that the cell type investigated was different in the two methods of analysis used: epithelial in direct preparations and fibroblastic in cell cultures. Thus, the results obtained in direct preparations indicate the BCC or SCC epithelial karyotype, whereas the aberrations found in cell cultures indicate the presence of chromosome instability in the fibroblastic stroma. The apparent lack of correspondence between direct and indirect preparations and the presence of clonal chromosome changes in both epithelial and stromal cells suggest tumor cell heterogeneity of BCC. The fibroblastic stroma seems to be implicated in the neoplastic process. This is not evident in SCC, in which clonal changes are present only in direct preparations. The chromosomal distribution of the breakpoints involved in structural changes in direct and cell culture preparations is random; together with those reported in the literature, the breakpoints found in BCC cultures show, however, a cluster to 1p36, 3q13, 9q22, 14p11, 15p11, and Xp11 bands. We did not find any significant correlations between BCC cytogenetic results and the clinical data (site, age, sex, recurrence). The incidence of cases of BCC (38%) and of SCC (100%) showing clonal chromosome changes agree with their benign and malignant nature, respectively. Finally, a significantly high incidence of constitutional inv(9) and dup(9)(q11q21) was found in the group of patients with BCC.

Characterization of a malignant eccrine poroma by cytogenetic and fluorescence in situ hybridization techniques

We have cytogenetically and by fluorescence in situ hybridization (FISH) analyzed short-term cultures from a malignant eccrine poroma, a type of tumor in which chromosomal abnormalities have previously not been reported. Combining the results from G-banding and FISH, the karyotype was interpreted as 50,XX,t(3;11;12)(q21;p15;q15),+5,+7,+9, +9,t(12;22)(q13;q13),+del(12)(q15),der(15)t(3;15) (q23;p13),der(17)t(8;17)(q22;p13),-20,add(22)(q13).