Concordance between karyotyping and in situ hybridization procedures in the detection of monosomy 9 in bladder cancer

Aneusomy for detection of bladder cancer recurrence: a Southwest Oncology Group study

The high risk of recurrence in superficial transitional cell cancer (TCC) of the bladder prompted evaluation of whether chromosome changes detected at first recurrence were correlated with relapse or with response to fluoroquinolone treatment. Fluorescence in situ hybridization analysis was applied to desquamated cells from bladder washings obtained immediately before surgical resection. Cells were screened for numeric changes in chromosomes 7 and 9. Aberrations were identified in 38/54 patients eligible for evaluation. Although no clear associations were established owing to sample size, the results suggested that risk of progression/relapse was positively associated with loss of chromosome 9 and with polysomy, and negatively associated with gain of chromosome 7, the latter in contrast to published data. A short-term survival advantage was noted anecdotally with gain of chromosome 9.

Chromosomal aberrations in transitional cell carcinoma: its correlation with tumor behavior

OBJECTIVE

Fluorescence in situ hybridization (FISH) was used to study numerical aberrations of chromosomes 1, 3, 7, 9, 11, 15, 17, X and Y in interphase nuclei of 16 transitional cell carcinoma (TCC) cell lines of the urinary tract. The number of chromosomal signal copies was compared with the DNA ploidy and correlated with the cellular grading and original tumor staging.

METHODS

The single-target FISH with the repetitive DNA probes for chromosomes 1, 3, 5, 7, 9, 11, 15, 17, X and Y were performed in 16 human TCC cell lines. For each test specimen, a minimum of 200 nuclei were analyzed. The number of fluorescent signals per nucleus was recorded. Tumor ploidy was analyzed using the DNA propidium iodide flow cytometric method. These results were correlated with tumor grade and stage.

RESULTS

In two diploid TCC cell lines, on average 67% of detected chromosomes were di-(i)somic. In 14 aneuploid TCC cell lines, on average only 10% (0-44%) of detected chromosomes were di-(i)somic. Chromosome X was completely changed into polysomism in 16 TCC cell lines (native male:female ratio = 12:4) but was unrelated to tumor grade or stage. Chromosome Y was lost in 10 out of 12 (83%) TCC cell lines which originated from male patients but was unrelated to tumor grade or stage too. 31% of chromosomes 11 and 15 were disomic in 16 TCC cell lines, 38% of chromosome 3 was monosomic, and 81-88% (83 in average) of chromosomes 1, 7, 9, 17 were polysomic. Disomic chromosome 11 associated with lower grade TCC and disomic chromosome 15 associated with higher grade TCC were noted (p < 0.01). Higher incidence of low stage tumors was observed in TCC cell lines with disomic chromosome 11 or chromosome 15 (p < 0.01). There was no correlation in somatic status of chromosomes 1, 7, 9, 17 with tumor grade and stage.

CONCLUSIONS

The results of the study demonstrate that polysomism of chromosomes 1, 7, 9, 17 and X occurs in most of the TCC cells with aneuploidy. The stability of chromosomes 11 and 15 is closely related to tumor grade and stage. The role of chromosome Y loss and monosomism of chromosome 3 in oncogenic relevant of bladder cancer is still unclear.

Molecular genetic analysis of chromosome 9 candidate tumor-suppressor loci in bladder cancer cell lines

Underrepresentation of chromosome 9 is a common finding in bladder cancer. Frequent loss of the whole chromosome suggests the presence of at least one relevant tumor suppressor gene on each arm. Candidate regions identified by loss of heterozygosity (LOH) analysis include a region at 9p21 containing CDKN2A, which encodes p16 and p14(ARF), a large region at 9q12-31 including PTCH and many other genes, a small region at 9q32-33, which includes the DBCCR1 gene, and a region at 9q34 including the TSC1 gene. Experimental replacement of genes or chromosomes into tumor cells with appropriate deletions or mutations represents an important approach to test the functional significance of candidate tumor suppressor genes. Loss of an entire copy of chromosome 9 in many bladder tumor cell lines provides no indication of which gene or genes are affected, and selection of appropriate recipient cells for gene replacement is difficult. We have investigated three candidate tumor suppressor genes on chromosome 9 (CDKN2A, DBCCR1, and TSC1), at the DNA level and by expression analysis in a panel of bladder tumor cell lines, many of which have probable LOH along the length of the chromosome, as indicated by homozygosity for multiple polymorphic markers. Cytogenetically, we found no reduction in the numbers of chromosomes 9 relative to total chromosome count. Homozygous deletion of the CDKN2A locus was frequent but homozygous deletion of TSC1 was not found. A new cell line, DSH1, derived from a pT1G2 transitional cell carcinoma with known homozygous deletion of DBCCR1, is described. This study identifies suitable cell lines for future functional analysis of both CDKN2A and DBCCR1.

Chromosome 9 aberrations by fluorescence in situ hybridisation in bladder transitional cell carcinoma

To investigate the role of the monosomy 9 in bladder carcinogenesis, 96 cases of superficial bladder transitional cell carcinoma (TCC) were studied and followed periodically for around 3 years (mean+/-standard error of the mean (SEM); 3.46+/-0.34 years). Samples from bladder washings were analysed by fluorescent in situ hybridisation (FISH) to detect numerical anomalies of chromosome 9. Moreover, to evaluate the relative under representation of this chromosome, we detected numerical changes of chromosome 8 and DNA ploidy by flow cytometric analysis (FCM). Chromosome 8 copy number were related to FCM DNA ploidy and both were related with tumour grade. Monosomy 9 did not correlate with tumour grade, stage, chromosome 8 aneuploidies and abnormal DNA content, but correlated with tumour progression. Comparing the results in the primary and subsequent tumours, we observed an increase in the frequency of aneuploidies by FCM, associated with an increase of chromosome 8 polysomies. The mean chromosome 9 copy number/nucleus remained nearly the same in most of the primary and invasive tumours. Our results confirm that monosomy 9 is an early event and that it is retained during tumour progression and invasion and that the loss occurs before the tetraploidisation process. The relationship between the presence of a sub-population with monosomy 9 and tumour progression suggests the presence of a region that could have a role in the progression of superficial bladder TCC.

Mutation of cell cycle regulators and their impact on superficial bladder cancer

Early cytogenetic studies in bladder cancer identify regions of chromosomal gain or loss that can be candidate loci for oncogenes and tumor suppressor genes. Oncogenes with potential prognostic significance identified in bladder cancer the RAS family, epidermal growth factor receptor, ERBB-2, MDM2, and cyclin D1. The TP53 gene has been the most thoroughly characterized tumor suppressor gene in bladder cancer, with correlation of TP53 alterations with type of carcinogenic exposure, tumor stage and grade, as well as prognosis. Studies evaluating alterations of the retinoblastoma pathway have identified the retinoblastoma gene, RB, p161NK4A/CDKN2, and E2F-1 as tumor suppressor genes with potential prognostic significance in patients with bladder cancer. Better understanding of the genetic mechanisms underlying bladder tumor development and progression will allow better prevention, diagnosis, and treatment strategies.

Basic research

Basic research is currently investigating the molecular cascade associated with bladder cancer development. Many new findings are potential leads towards the improvement of the diagnosis and prognosis of this disease. Special care, however, should be taken in the design of protocols for clinical evaluation of the value of these markers. Some initial guidelines have been put forward in this report.