Genes controlling genetic stability in sqamous cell carcinoma of larynx

MM Sasiadek MD^a, S Kozlowska MD^a, K Schlade-Bartusiak PhD^a, R Smigiel MD^b,c, D Ramsey PhD, T Kayademir PhD^d, N Blin PhD^d

^aDepartment of Genetics, ^bDeptartment of Pathophysiology; Wroclaw Medical University, Wroclaw, Poland, ^cTechnical University, Institute of Mathematics, Wroclaw, Poland, ^dDivision of Molecular Genetics, Eberhard Karls University, Tübingen, Germany

AIM: Carcinogenesis results from the accumulation of genetic alterations forming a network; genetic instability is one of the cardinal features of cancer. However, the events leading to genomic instability in larynx squamous cell carcinoma (LSCC) have still not been disclosed.The aim of our study was to describe genetic alterations forming a network in the control of genetic stability in LSCC. METHODS: The study group comprised 52 patients, diagnosed with primary LSCC. Loss of heterozygosity (LOH) analysis was applied in testing for genes important in carcinogenesis. The expression of those genes found with the highest LOH frequency as well as for CCND1 was assessed by immunostaining. Microsatellite instability (MSI) was monitored by BAT26, BAT25, and BAT40. In searching for chromosomal imbalances (CI) comparative genomic hybridization (CGH) was used. The difference between two population means was tested by using the student t-test and Wilcoxon’s rank test. More complicated relations were analyzed by means of Kendall’s test of correlation and analysis of variance (ANOVA). RESULTS: The highest frequency of LOH was found for CDKN2A (55.4%), MLH1 (46.0%) and RB1 (35.7%). In LSCC LOH tends to occur together in gene pairs or triplets. The pair MLH1 / CDKN2A and triplets MLH1 / TSG on 8p22 / CDKN2A and MLH1 / CDKN2A / RB1, are related to staging and grading. The alterations in protein expressions were observed: a decrease in RB1 and CDKN2A in 10.2% and 45.7%; an increase in CCND1 in 47.05%, and decrease in MLH1 in 22.72% of cases. MSI analysis showed a microsatellite stable phenotype in 95.2% of analyzed cases. In the set of analyzed tumors 1720 chromosomal imbalances were observed. We classified 25 tumors as instable with respect to chromosomal losses and 24 tumors as instable with respect to chromosomal gains. LOH in CCND1/MLH1 showed a correlation with increase in chromosomal gains (p<0.01) as well as with grading (p<0.01). CONCLUSIONS: 1. In SCCL frequent LOH, but no significant microsatellite instability is observed. It can be hypothesized that a suppressor pathway plays a dominant role in the etiology of SCCL. 2. MLH1 inactivation could have other consequences in SCCL than controlling of mismatch repair. 3. RB1 pathway is altered in HNSCC, with CDKN2A, rather than RB1 being more frequently inactivated. 4. MLH1 and CCND1 play an important role in LSCC development and progression. 5. CCND1 and MLH1 form a functional network in controlling chromosomal imbalances in larynx cancer.

Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Nice, France; February 7 - 10, 2004; in oral session 796 (Genetic instability).