Chromosomal alterations in early stages of malignant mesotheliomas.

In a case of a 67-year-old man with two different early stages of a predominantly epithelioid mesothelioma ("mesothelioma in situ", "early-stage mesothelioma"), chromosomal imbalances were determined by comparative genomic hybridisation (CGH), a molecular cytogenetic technique to detect chromosomal gains and losses in tumour cells. In the case of the mesothelioma in situ cells, nine different chromosomal alterations could be detected (losses on 3p, 5q, 6q, 8p, 9p, 15q, 22q, Y; gain on 7q), whereas the early-stage mesothelioma showed the same defects except for the gain on 7q. The simultaneous losses of 6q, 9p and 22q, as well as other chromosomal regions, correlate well with the most common defects previously found in 90 cases of more-advanced-stage mesotheliomas using CGH. These data demonstrate that initial chromosomal defects in early stages of mesotheliomas can be detected by conventional CGH in combination with laser microdissection. The molecular cytogenetic findings support the histological diagnosis of a pleural mesothelioma. The surprisingly high number and extent of genomic alterations found in the examined case probably reflects the genomic instability in the tumour cells and indicates a "genetic chaos" even in earlier stages of malignant mesotheliomas.

Pathological anatomy and molecular pathology.

The incidence of malignant mesotheliomas in Germany has increased since about the mid 1980s, and a further increase is expected until about 2020 due to the peak in asbestos processing in Germany between 1965 and 1980. About 90% of the mesotheliomas recorded in the files of the German Mesothelioma Registry in Bochum are asbestos-related and therefore possibly due to an occupational exposure. In 2003, 717 mesotheliomas were newly diagnosed at the German Mesothelioma Registry. Mesotheliomas are very heterogeneous in terms of histological appearances and of prognosis. At present, the diagnostic gold standard is conventional histology in combination with additional immunohistochemical analysis. We were not able to confirm a promising report that described telomerase reverse transcriptase catalytic subunit (TERT) for the differentiation between reactive and neoplastic mesothelial lesions, which can be extremely difficult. DNA cytometric analysis may also help differentiate between reactive and neoplastic mesothelial lesions. There are some characteristic patterns of chromosomal imbalances as detectable by comparative genomic hybridization (CGH), but at present, specific chromosomal or genetic defects that give rise to a mesothelioma are not known. A reliable pathological diagnosis is the basis for therapeutic, prognostic, and medicolegal consequences. In general, it can be achieved by thoracoscopic inspection with specifically directed biopsy. Furthermore, a description of the peculiarities of each mesothelioma by the pathologist might be the key to a more individual therapy in the future.

Mutational analysis of the nf2 tumour suppressor gene in three subtypes of primary human malignant mesotheliomas.

Fourteen primary human malignant mesothelioma (HMM) samples obtained from 14 patients were screened for point mutations and microdeletions/microinsertions in exons 1-16 of the chromosome 22q-located tumour suppressor gene neurofibromin 2 (nf2) by single strand conformation polymorphism (SSCP) analysis. In one tumour (7%) a 10 basepair microdeletion of exon 10 was detected by SSCP and subsequently characterised in detail by sequencing. Deletion of the second nf2 allele in laser-microdissected regions of the 10 bp mutation-harbouring tumour was demonstrated by denaturing gradient gel electrophoresis (DGGE) analysis. Simultaneous comparative genomic hybridisation (CGH) analysis also showed losses at chromosome 22q. Our data indicate that functional loss of the NF2 protein may be involved in the formation of a subset of HMMs.

Molecular cytogenetic differences between histological subtypes of malignant mesotheliomas: DNA cytometry and comparative genomic hybridization of 90 cases.

It is established that subtypes of human malignant mesotheliomas (MM) are associated with different survival times. Ninety cases of MM were examined using DNA cytometry and comparative genomic hybridization (CGH), with emphasis on the main histological subtypes; epithelioid, sarcomatoid and biphasic. A comparison by DNA cytometry revealed moderate differences, with the rare subgroup of mesodermomas having the highest and the sarcomatoid group the lowest rate of aneuploidy. Using CGH, 6.2 chromosomal imbalances per case on average could be detected. Losses (4.1/case) were more common than gains of chromosomal material (2.1/case). MM show no single, specific defect, but a typical pattern of genomic defects can be attributed to this tumour entity. Common losses are clustered at the chromosomal regions 9p21 (34%), 22q (32%), 4q31-32 (29%), 4p12-13 (25%), 14q12-24 (23%), 1p21 (21%), 13q13-14 (19%), 3p21, 6q22, 10p13-pter and 17p12-pter (16% each). Common gains are located on 8q22-23 (18%), 1q23/1q32 (16%), 7p14-15 and 15q22-25 (14% each). While differences in the frequencies of the defects between epithelioid and sarcomatoid MM are not as pronounced as are seen with the pleomorphic mesodermomas, several chromosomal locations (3p, 7q, 15q, 17p) show significant variations. The most pronounced distinguishing feature of sarcomatoid MM is a more than fourfold higher number of amplicons. These data indicate that MM has a distinctive tumour biology with a broad spectrum of heterogeneity, as reflected in morphology and also, more subtly, in the patterns of chromosomal imbalances of the subtypes.