| Abstract |
Carcinoma of the cervix is one of the most common tumors affecting women world-wide, both in incidence and mortality, predominantly in the developing countries, with approximately 500 000 new cases diagnosed annually. The existing screening methods for cervical cancer such as Pap smear, cancer biochemical markers and colposcopy fail to detect early enough, a significant percentage of cervical cancer or CIN cases. The genetic events implicated in the initiation and progression of this disease remain an important challenge in gynecological research. Great improvements has been achieved in defining gene defects and in discovering new genes that are involved in this disease. The microsatellite alterations (MA), such as Microsatellite Instability (MIN) and Loss of Heterozygocity (LOH) seem to play an important role among the molecular approaches of studying the disease. It has been suggested that the detection of instability of the genom might be useful in the early detection of human cancers. The purpose of this study was whether MIN and LOH phenomena can be detected in DNA extracted from solid tumors and cytological material of patients with cervical cancer (CC) or cervical intraepithelial neoplasia (CIN). The demonstration of genetic imbalance in exfoliated cervical cells might be a new screening test for early detection or a supplementary diagnostic method for CC and CIN. It could also contribute in a closer screening approach for high risk women for the disease. Using polymerase chain reaction-based microsatellite analysis and 18 microsatellite markers we examined samples obtained from 63 patients with CIN, 40 patients with CC and 20 healthy donors. These 18 markers are located at p16, BRCA2, p53, BRCA1 and candidate tumor suppressor loci, on 9pter-p13, 13q12, 17p13, 17q11-q22 and 9q32-q34, respectively. Our microsatellite DNA assay for the 18 examined markers demonstrated 87,5% incidence of LOH. The 9pter-p13 locus was affected in 67,5% of cases approximately 2-, 3- and 5-fold more frequently than 13q12, 9q32-q34 and 17q12-q22, respectively. LOH phenomenon was detected in 55.5% of patients with CIN. The 9pter-p13 was affected in 41.3% of cases approximately 2-, 4- and 5-fold more frequently than 13q12, 9q32-q34 and 17q12-q22, respectively. MIN was detected in 7.4% of patients with CC while none of the CIN patients fulfilled the criterion of the co-finding of at least five markers to be characterized as MIN positive phenotype. However the latter does not diminish the importance of MIN detection since this subset of tumors possibly harbors alterations in the mismatch DNA repair system and therefore may represent a distinct pathway of cervical carcinogenesis. None of the healthy donors exhibited any genetic alterations. We conclude that microsatellite markers which are located on 9pter-p13 region proximal to 9p21 region where p16 gene is mapped reveal an increase of allelic imbalance, while distal from this region LOH frequency declined. Therefore, p16 gene might be implicated in the pathogenesis of CC and CIN. High instability of microsatellite markers near p16 gene in solid tumor or exfoliative cells of the female genital tract might prove helpful in diagnosing the dysplastic lesions of the cervix or a predisposition to it. We showed for the first time in specimens with CIN and early stages of CC that microsatellite alterations is a detectable phenomenon in the exfoliated cells of the female genital tract with possible clinical application in early detection of CC or CIN. From our results we could conclud that LOH and MIN phenomena might be used as a non-invasive, inexpensive and relatively easy performed screening test for CC and CIN in cytological material.
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Αστάθεια μικροδορυφορικών DNA σε καρκίνους και προκαρκινικές αλλοιώσεις του γυναικείου γεννητικού συστήματος
