Multiple cytogenetic clones in a basal cell carcinoma

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.

Trisomy 6 in basal cell carcinomas correlates with metastatic potential: a dual color fluorescence in situ hybridization study on paraffin sections

BACKGROUND

Most basal cell carcinomas (BCCs) are indolent lesions; a few become locally aggressive or even metastatic. Little is known about the molecular and genetic alterations in this malignant transformation. Conventional karyotyping in BCC has revealed a high frequency of nonclonal, structural rearrangements, with few cases that show multiple, unrelated, small clones suggestive of a multicellular origin. Trisomy 6 was described recently in a few BCCs, but the biologic significance of the appearance of trisomy 6 in BBCs was not clear.

METHODS

Thirty cases including 4 metastatic, 4 locally aggressive, and 22 conventional nonaggressive BCCs were studied. Fluorescence in situ hybridization (FISH) was performed on 4 microm tissue sections, using alpha-centromeric enumeration probes for chromosome 6 (SpectrumGreen, Vysis Inc., Downers Grove, IL) and chromosome 4 (SpectrumOrange, Vysis Inc., Downers Grove, IL, used as disomic cell control). Trisomy 6 was semiquantitated within tumor cells and nonneoplastic cells in each case.

RESULTS

Trisomy 6 was identified in all 4 metastatic BCCs within tumor cells and in corresponding BCCs at the primary cutaneous site in 2 of these 4 cases. Two locally aggressive BCCs, 1 of which had preceding radiation exposure, also showed trisomy 6. All nonaggressive BCCs and nonneoplastic cells were disomic for chromosome 6.

CONCLUSIONS

Trisomy 6 has been identified as a cytogenetic aberration representative of tumor cells in aggressive and metastatic BCC. None of the nonaggressive BCCs in this study demonstrated trisomy 6. Acquisition of trisomy 6 by tumor cells in BCC may lead to the emergence of metastatic potential. Additional studies to define the underlying mechanisms may be valuable in preventing aggressive behavior in BCC.

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.

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.

Chromosome breakpoint distribution in nonmelanoma skin cancers

We have identified chromosome regions that may be sites of genes activated as a result of chromosomal rearrangements observed in 61 of the 86 skin tumors referenced in the literature. The data showed that most of the breakpoints were distributed throughout the genome and some tended to cluster. Highest frequencies of breakpoints were observed in chromosomes with high relative length, except chromosomes 14 and 15 that were often affected in malignant tumors, despite their size. Our work provides a starting point for more detailed studies that may allow identification of these genes as important keys in the development and progression of skin cancers.

Trisomy 7 in keratoacanthoma and squamous cell carcinoma detected by fluorescence in-situ hybridization

Keratoacanthoma (KA) is generally considered to be a clinically and histologically distinct entity, but it often remains difficult to separate from well-differentiated squamous cell carcinoma (WDSCC). Recently, trisomy 7 has been identified in squamous cell carcinoma of the skin. In this study, we examined classical KA (n = 6), WDSCC (n = 7) and squamous cell carcinoma with KA-like features (SCC-KA) (n = 8) for trisomy 7 by fluorescence in-situ hybridization (FISH) to determine if this chromosomal abnormality is unique to squamous lesions diagnosed as WDSCC, or shared by both KA and SCC. In addition, the pertinent clinical-histopathologic findings were summarized. Trisomy 7 was identified in one KA, one SCC-KA and two WDSCC. This study demonstrates that there is a chromosomal abnormality shared by KA and SCC, providing further evidence that KA is most likely a form of SCC. Further studies are required to determine if trisomy 7 in these lesions is of prognostic significance.

Cytogenetic study of neoplastic and nonneoplastic cells of the skin

We describe the cytogenetic study of six neoplastic and eight nonneoplastic skin samples from sun-exposed body sites or sites close to tumors. The cytogenetic findings revealed that chromosome rearrangements are common in sun-exposed normal skin, similar to the situation in cutaneous tumors, and suggest that such karyotypic abnormalities might be indicative of the genetic instability caused by specific mutations and resulting from carcinogenic exposure of the tissue.

Cytogenetic findings in two basal cell carcinomas

We describe the cytogenetic study of two basal cell carcinomas. Only single chromosomally abnormal clones could be detected in both. In addition, many nonclonal changes were seen in the samples, which may represent small neoplastic clones or the result of a basic molecular defect induced by carcinogens.

Trisomy 7 in nonneoplastic cells

The somatic mutation theory of tumorigenesis states that mutations are necessary for tumor development. On the other hand, acquired, clonal chromosomal alterations are occasionally detected in otherwise normal, nonneoplastic cells--for example, loss of sex chromosomes occurs in bone marrow cells and lymphocytes in elderly individuals--and it is therefore evident that not all mutations are by themselves sufficient for neoplasia to occur. Thus, the finding of an acquired, clonal chromosomal abnormality does not constitute proof that a lesion is neoplastic. Trisomy 7 has, as the sole clonal chromosomal aberrations, been reported in a wide variety of epithelial tumor types but also in some mesenchymal and neurogenic neoplasms. It has been suggested to be a primary, i.e., tumor-initiating, abnormality in tumors of the bladder, brain, colon, kidney, lung, ovary, prostate, and thyroid. But data from cytogenetic studies of solid tumors, macroscopically normal tissue in the proximity of solid tumors, and nonneoplastic lesions now question the importance of a solitary +7 as a neoplasia-associated change. Most solid tumors in which trisomy 7 has been found as the sole change in one clone have also displayed other, cytogenetically unrelated, clones with complex karyotypic abnormalities. Such karyotypic differences among coexisting clones could indicate that the neoplasm is polyclonal, that the cytogenetically disparate clones have emerged during tumor progression from one original clone carrying submicroscopic genomic changes only, or that the clone with +7 does not represent the tumor parenchyma. The latter interpretation is supported by the finding of cells with trisomy 7 in macroscopically normal tissue outside tumors of the brain, kidney, and lung.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromosome studies of solid tumours

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Clonal structural chromosome aberrations in nonneoplastic cells of the skin and upper aerodigestive tract

Cytogenetic analyses of tumors of the skin and upper aerodigestive tract have repeatedly revealed small, pseudodiploid clones characterized by balanced structural rearrangements and a high frequency of cells with nonclonal structural aberrations. However, the lack of common cytogenetic denominators within the different histologic subtypes, the discrepancy between cytogenetic findings and data obtained from flow cytometric DNA content studies, and the occasional identification of tumors with massively rearranged karyotypes indicate that the chromosome rearrangements present in pseudodiploid cells have little to do with the tumorigenesis or progression. Further support for this conclusion, and indirect evidence that the pseudolipid clones probably do not represent the tumor cell populations, derives from the present study in which clonal and nonclonal structural rearrangements were also found in short-term cultures from nonneoplastic skin and pharyngeal mucosa. It is possible that the aberrations are present in subepithelial fibroblast that have accumulated DNA damage due to extensive exposure to potentially carcinogenic agents.