Pharmacogenetics in cancer therapy - 8 years of experience at the Institute for Oncology and Radiology of Serbia.

PURPOSE: Pharmacogenetics is a study of possible mechanism by which an individual's response to drugs is genetically determined by variations in their DNA sequence. The aim of pharmacogenetics is to identify the optimal drug and dose for each individual based on their genetic constitution, i.e. to individualize drug treatment. This leads to achieving the maximal therapeutic response for each patient, while reducing adverse side effects of therapy and the cost of treatment. A centralized pharmacogenetics service was formed at the Institute for Oncology and Radiology of Serbia (IORS) with the aim to provide a personalized approach to cancer treatment of Serbian patients. METHODS: Analyses of KRAS mutations in metastatic colorectal cancer, EGFR mutations in advanced non-small cell lung cancer, CYP2D6 polymorphism in breast cancer, DPD polymorphism in colorectal cancer and MTHFR polymorphism in osteosarcoma have been performed by real time polymerase chain reaction (PCR) and PCR-restriction fragment length polymorphism (PCR-RFLP). RESULTS: Mutation testing analyses were successful for 1694 KRAS samples and 1821 EGFR samples, while polymorphism testing was successful for 9 CYP2D6 samples, 65 DPD samples and 35 MTHFR samples. CONCLUSIONS: Pharmacogenetic methods presented in this paper provide cancer patients in Serbia the best possible choice of treatment at the moment.

Overall human papilloma virus and types 16/18 prevalence in women with normal cervical cytology in Serbia: is it time for human papillomavirus testing and/or vaccination?

PURPOSE: Infection with high-risk human papilloma viruses (HR-HPV), especially types 16/18, is the main factor in cervical carcinogenesis. Although the incidence of cervical cancer in Serbia is among the highest ones in Europe, data about HPV infection are insufficient. The aim of this study was to investigate the presence of overall and HPV16/18 infections in women with healthy appearance and cytologically (Pap) normal cervix. METHODS: The study was performed on women who participated in this cervical cancer screening pilot study. Cervical HPV infection was detected by GP5+/6+ PCR. HPV16/18 were detected by amplification of E7/E1 viral gene, respectively. RESULTS: In 350 women we got the following results: cytological abnormalities (10.3%); visible cervical changes (20.3%); previous precancerous lesion (2.3%); normal Pap and speculum finding without history of precancerous lesion (67.1%). In the last group overall HPV prevalence was 41.3%, with 10.5% HPV16 and 23.7% HPV18. The rate of multiple HPV16 plus HPV18 infections was 2.6%. HR-HPV16/18 comprised 31.6% of the total HPV positive participants. CONCLUSION: Owing to the high prevalence of overall and HPV16/18 infections in women with healthy appearance and cytologically normal cervix, we postulate that testing/ prophylaxis for these HR-HPV types could be introduced in cervical cancer screening and preventive programmes in Serbia.

The influence of methylenetetrahydrofolate reductase and thymidylate synthetase gene polymorphisms on lung adenocarcinoma occurrence.

PURPOSE: Methylenetetrahydrofolate reductase (MTHFR) and thymidylate synthetase (TYMS) are suggested as risk factors for lung cancer. The purpose of this study was to analyze the association of MTHFR C677T polymorphism and variable number tandem repeat 2R/3R and single nucleotide polymorphism G>C in the 3R allele of the TYMS gene with lung adenocarcinoma. METHODS: A case-control study including lung adenocarcinoma patients and healthy subjects was performed. Restriction fragment length polymorphism analysis was used for genotyping. Descriptive analyses included genotype and allelic frequencies; the odds ratio and 95% confidence interval were calculated as an estimate of relative risk. Significance was set at p<0.05. RESULTS: A significant difference in CC vs TT+CT MTHFR genotype distribution was observed between patients and controls. There was no significant association between the TYMS polymorphisms and the risk of lung adenocarcinoma. CONCLUSIONS: The MTHFR 677T allele is likely to have a protective effect against lung adenocarcinoma development.

RAD51 135G>C and TP53 Arg72Pro polymorphisms and susceptibility to breast cancer in Serbian women.

Breast cancer is a complex disease with both genetic and environmental factors involved in its etiology. An important role of polymorphisms in genes involved in DNA repair has been reported related to breast cancer risk. We conducted a case-control study in order to investigate the association of RAD51 135G>C and TP53 Arg72Pro polymorphisms with breast cancer in Serbian women.48 BRCA negative women with breast cancer and family history of breast/ovarian cancer (hereditary group), 107 women with breast cancer but without family history of the disease (sporadic group) and 114 healthy women without a history of the disease (control group) were included. Restriction fragment length polymorphism was used for genotyping. Genotype and allelic frequencies, the odds ratio (OR) and the 95 % confidence interval (CI) were calculated as an estimate of relative risk. The Hardy-Weinberg equilibrium was tested using χ(2) test. Significance was considered for p < 0.05. RAD51 135G>C showed statistically significant association of CC genotype and increased breast cancer risk (OR 10.28, 95 % CI 1.12-94.5) in hereditary group of patients compared to the control group. Regarding the TP53 Arg72Pro, we showed statistical significance for ProPro + ProArg comparing to ArgArg (OR 2.34, 95 %, CI 1.17-4.70) in hereditary compared to sporadic group. RAD51 135G>C contributes to hereditary breast cancer in Serbian population, with CC genotype as a risk factor. We also found that carriers of Pro allele of TP53 codon 72 is related to hereditary cancer comparing to sporadic one, which indicates it as a potential risk factor for hereditary form of disease.

Serbian high-risk families: extensive results on BRCA mutation spectra and frequency.

Mutations in BRCA genes elevate risk for breast and ovarian cancer. These mutations are population specific. As there are no data on BRCA mutation screening on larger number of probands in Serbia to date, aim of this study was to determine types and frequencies of BRCA mutations in individuals from high-risk families from Serbia, as well as to determine which BRCA mutations may be considered as founder for Serbian population. We analyzed 94 probands and detected 9 frameshift mutations in 12 individuals, 1 benign BRCA2 nonsense mutation and numerous missense and synonymous mutations in both genes. Frequency of frameshift mutations is 12.77%. In addition to two novel mutations detected in our population we reported previously, we detected another novel mutation--c.7283delT in BRCA2 exon 14. None of the detected deleterious mutations may be considered as founder mutations for Serbian population, as each of them was found in no more than two high-risk families. This mutation diversity is most probably due to high migration rate in history of this part of Europe. Interpretation of genetic testing results with missense mutations of unknown clinical importance is very challenging and should be approached with caution, using all available data sources for results' interpretation.

TP53 codon 72 polymorphism and risk of cervical carcinoma in Serbian women.

PURPOSE: It was shown that individuals homozygous for the Arg-encoding allele of codon 72 TP53 gene may have an increased risk to human papillomavirus (HPV)-related cervical carcinomas. However, many studies have failed to confirm this hypothesis. The aim of this study was to investigate a role of the TP53 codon 72 polymorphism in cervical carcinoma development in Serbian women. METHODS: In comparative, prospective study, we analyzed 49 wild type TP53 gene cervical carcinomas samples and 74 cervical smears of gynecologically healthy women. DNA was extracted by salting-out procedure. Codon 72 polymorphism was assessed by Restriction Fragment-Length Polymorphism method. Presence of HPV infection was detected through amplification of one part of L1 viral gene. χ(2) and odds ratio were used for statistical analysis. RESULTS: The distribution of Arg/Arg, Arg/Pro, and Pro/Pro genotypes of codon 72 of TP53 gene was: 63.3, 34.7, and 2.0 % in the cervical carcinomas and 58.1, 33.8, and 8.1 % in the control group. We observed an increased risk for the development of cervical carcinoma for Arg homozygotes in relation to heterozygotes plus Pro homozygotes (OR 1.24; 95 % CI 0.59-2.61) and higher one for Arg/Arg plus Arg/Pro genotype in relation to Pro homozygotes (OR 4.24; 95 % CI 0.49-36.32). CONCLUSIONS: The results indicate that carriers of Arg allele of codon 72 TP53 gene have an increased risk for development of cervical carcinoma in Serbian women. However, the influence is not statistically significant and requires analysis of larger case-control group.

The usability of allele-specific PCR and reverse-hybridization assays for KRAS genotyping in Serbian colorectal cancer patients.

BACKGROUND: Colorectal cancers (CRCs) with wild-type KRAS respond to EGFR-targeted antibody treatment. Analysis of the hotspot clustered mutations in codons 12 and 13 is compulsory before therapy and no standardized methodology for that purpose has been established so far. Since these mutations may have different biological effects and clinical outcome, reliable frequency and types of KRAS mutations need to be determined for individual therapy. AIMS: The purpose of this study was to describe the KRAS mutation spectrum in a group of 481 Serbian mCRC patients and to compare the general performances of allele-specific PCR and reverse-hybridization assays. METHODS: KRAS testing was performed with two diagnostic analyses, DxS TheraScreen K-RAS PCR Kit and KRAS StripAssay™. RESULTS: KRAS mutations in codons 12 and 13 were present in 37.6 % of analyzed formalin-fixed paraffin-embedded (FFPE) DNA samples. The seven most frequent mutation types were observed with both assays: p.G12D 34.6 %, p.G12V 24.9 %, p.G12A 10.3 %, p.G12C 8.1 %, p.G12S 5.4 %, p.G12R 1.6 %, and p.G13D 15.1 %. Regarding double mutants, 0.8 % of them were present among all tested samples and 2.2 % among KRAS mutated ones. CONCLUSIONS: Two screening approaches that were used in this study have been shown as suitable tests for detecting KRAS mutations in diagnostic settings. In addition, they appear to be good alternatives to methods presently in use. In our experience, both methods showed capacity to detect and identify double mutations which may be important for potential further subgrouping of CRC patients.