Molecular Determinants of Colon Cancer Susceptibility in the East and West.

The currently available knowledge of factors that dictate the development and progression as well as the clinical outcome of colorectal cancers (CRC) is mainly derived from Western countries. Considerable number of publications document different incidence rates and contrasting clinical features of CRC in various groups such as the differences between urban vs. rural areas, young vs. old age and the East vs. the West. In particular, Egyptian CRC is a surprisingly young age disease with higher proportion of poorly differentiated and advanced stage cancers as compared to the Western counterparts. Less number of publications addressed the molecular genetics and epigenetic basis of these differences. The available data on CRC and other cancers support a substantial role of several environmental risk factors which impinge on the epigenome and alter the overall cellular and tissue homeostasis. Thus, environmental factors could play a role in predisposition to CRC in general as well as in shaping distinct disease phenotypes in different settings. On the other hand, the environment offers a wide range of preventive modalities including a selection of dietary chemopreventive agents which could play a significant role in fighting cancer at early stages. We here compare the clinical and molecular characteristics of Eastern and Western CRC based on the latest literature. The genetic, epigenetic and environmental etiologies for the observed differences are discussed. Finally, prospects for cancer prevention in light of the increased etiologic understanding are outlined.

SU-E-E-04: Building and Strengthening the First Master's Program in Medical Physics in The Gulf Region.

PURPOSE: The first medical physics Master's program in the Arabian Gulf region was started in 2002 at King Fahd University of Petroleum & Minerals (KFUPM), Dhahran, Saudi Arabia. METHODS: After consulting with national and international representatives from the AAPM, IOMP, the University of Wisconsin-Madison and King Faisal Specialist Hospital and Research Center (KFSHRC) we constructed a versatile and rigorous curriculum. The program requires the completion of 7 core courses, 7 required labs, a minimum of 3 elective courses, a research project, a four-month clinical rotation and passing and a comprehensive examination. The success of the program required very close collaboration with national hospitals such as King Fahad Specialist Hospital in Dammam (KFSH-D), KFSHRC, and Riyadh Military Hospital. We cemented the collaboration with a formal agreement between KFUPM and KFSH-D, whereby the clinical medical physicists are actively involved in teaching lectures and labs, evaluating students' performance and co-supervising their clinical rotation and research projects. In order to prepare our graduates for their medical physics careers, we emphasize innovative learning methods such as students centered learning, execution of course projects, experiential learning and acquiring research skills and tools such as Monte Carlo simulations. RESULTS: Our graduates have succeeded in securing clinical positions in some of the best hospitals in the region and achieved high employer satisfaction. Some students have gone to pursue their PhD's in North America and Europe. Many of our students succeeded in publishing their projects in international journals and international conferences. One of our students was instrumental in obtaining a US patent (US Patent # 785298) for an innovative x-ray tube design. CONCLUSIONS: We have achieved national recognition through the excellence of our graduates. In order to maintain high education quality standards and achieve international recognition, we are presently working to acquire IAEA approval and CAMPEP accreditation.

Potential role of a navigator gene NAV3 in colorectal cancer.

BACKGROUND: The recently described navigator proteins have a multifaceted role in cytoskeletal dynamics. We report here on the relevance of one of them, navigator 3 (NAV3), in colorectal cancer (CRC). METHODS: We analysed changes in chromosome 12 and NAV3 copy number in CRC/adenoma samples of 59 patients and in 6 CRC cell lines, using fluorescence in situ hybridisation, loss of heterozygosity, and array-CGH. NAV3 target genes were identified by siRNA depletion, expression arrays, and immunohistochemistry. RESULTS: NAV3 deletion and chromosome 12 polysomy were detected in 30 and 70% of microsatellite stability (MSS) carcinomas, in 23 and 30% of adenomas and in four of six CRC cell lines. NAV3 amplification was found in 25% of MSS samples. NAV3 alterations correlated with lymph node metastasis. In normal colon cells, NAV3 silencing induced upregulation of interleukin 23 receptor (IL23R) and gonadotropin releasing hormone receptor. In MSS and microsatellite instability tumours, IL23R immunoreactivity correlated with Dukes' staging and lymph node metastases, whereas nuclear beta-catenin correlated with lymph node metastases only. CONCLUSION: NAV3 copy number changes are frequent in CRC and in adenomas, and upregulation of IL23R, following NAV3 silencing, strongly correlates with Dukes' staging and lymph node metastases. This suggests that NAV3 has a role in linking tissue inflammation to cancer development in the colon.

Clinic based transfer of the N(D,W)(60Co) calibration coefficient using a linear accelerator.

Ionization chambers used for reference dosimetry require a local secondary standard ionization chamber with a 60Co absorbed dose to water calibration coefficient N(D,W)(60Co) traceable to a national primary standards dosimetry laboratory or an accredited secondary dosimetry calibration laboratory. Clinic based (in-house) transfer of this coefficient to tertiary reference ionization chambers has traditionally been accomplished with chamber cross calibration in water using a 60Co beam; however, access to 60Co teletherapy machines has become increasingly limited for clinic based physicists. In this work, the accuracy of alternative methods of transferring the N(D,W)(60Co) calibration coefficient using 6 and 18 MV photon beams from a linear accelerator in lieu of 60Co has been investigated for five different setups and four commonly used chamber types.

Differential cancer predisposition in Lynch syndrome: insights from molecular analysis of brain and urinary tract tumors.

Hereditary non-polyposis colorectal carcinoma (Lynch syndrome) is among the most common hereditary cancers in man and a model of cancers arising through deficient DNA mismatch repair (MMR). Lynch syndrome patients are predisposed to different cancers in a non-random fashion, the basis of which is poorly understood. We addressed this issue by determining the molecular profiles for different tumors from a nationwide cohort of Lynch syndrome families (approximately 150 tumors in total). We focused on some less prevalent cancers, affecting the brain (n = 7) and urinary tract (five bladder and five ureter uroepithelial cancers and four kidney adenocarcinomas), and compared their molecular characteristics to those of the most common cancers, colorectal, gastric and endometrial adenocarcinomas, from the same families. Despite origin from verified MMR gene mutation carriers, the frequency of high-level microsatellite instability in tumors varied between high (100-96% for ureter, stomach and colon), intermediate (63-60% for endometrium and bladder) and low (25-0% for kidney and brain). In contrast to gastrointestinal and endometrial carcinomas, active (nuclear) beta-catenin was rare and KRAS mutations were absent in brain and urological tumors. Compared with other tumors, frequent stabilization of p53 protein characterized urinary tract cancers. Promoter methylation of tumor suppressor genes discriminated the tumors in an organ-specific manner. Our findings suggest that different Lynch syndrome tumors develop along different routes. Uroepithelial cancers of the ureter (and bladder to lesser extent) share many characteristics of MMR deficiency-driven tumorigenesis, whereas brain tumors and kidney adenocarcinomas follow separate pathways.

Is gastric cancer part of the tumour spectrum of hereditary non-polyposis colorectal cancer? A molecular genetic study.

BACKGROUND: Gastric cancer is the second most common extracolonic malignancy in individuals with hereditary non-polyposis colorectal cancer (HNPCC)/Lynch syndrome. As gastric cancer is relatively common in the general population as well, it is not clear whether or not gastric cancer is a true HNPCC spectrum malignancy. AIM: To determine whether or not gastric cancer is a true HNPCC spectrum malignancy. SUBJECTS AND METHODS: The molecular and clinicopathological profiles of gastric cancers (n = 13) from HNPCC mutation carriers were evaluated and compared with the profiles of sporadic gastric cancers (n = 46) stratified by histology and microsatellite instability (MSI) status. RESULTS: This study on sporadic and HNPCC gastric cancers revealed several important universal associations. Loss of heterozygosity in the adenomatous polyposis coli (APC) region was associated with intestinal histology regardless of the MSI (p = 0.007). KRAS-mutations (p = 0.019) and frameshift mutations in repeat tracts of growth-regulatory genes (p<0.001) were associated with MSI tumours being absent in microsatellite stable (MSS) tumours. The average number of methylated tumour suppressor gene loci among the 24 genes studied (methylation index) was higher in MSI than in MSS tumours regardless of histology (p<0.001). Gastric cancers from HNPCC mutation carriers resembled sporadic intestinal MSI gastric cancers, except that MLH1 promoter methylation was absent (p<0.001) and the general methylation index was lower (p = 0.038), suggesting similar, but not identical, developmental pathways. All these lacked the mismatch repair protein corresponding to the germline mutation and displayed high MSI. CONCLUSION: The present molecular evidence, combined with the previous demonstration of an increased incidence relative to the general population, justify considering gastric cancers as true HNPCC spectrum malignancies.

Mechanisms of inactivation of MLH1 in hereditary nonpolyposis colorectal carcinoma: a novel approach.

Mutations in the DNA mismatch repair gene MLH1 are a major cause of hereditary nonpolyposis colorectal cancer (HNPCC). No mutant phenotype is observed before the wild-type (wt) allele is somatically inactivated in target tissue. We addressed the mechanisms of MLH1 inactivation in 25 colorectal (CRC) and 32 endometrial cancers (ECs) from MLH1 mutation carriers (Mut1, in-frame genomic deletion; Mut2, out-of-frame splice site mutation; Mut3, missense mutation). By a quantitative method, matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF), utilizing four intragenic single nucleotide polymorphisms and mutations, loss of heterozygosity (LOH) was present in 31/57 (54.4%) of tumors. The wt allele displayed LOH more often than the mutant allele (23/57 vs 8/57, P=0.006). For Mut1, LOH was more frequent in CRC than EC (10/11 vs 1/13, P<0.0001), whereas Mut2 and Mut3 displayed opposite LOH pattern. Moreover, although wt LOH predominated in CRC irrespective of the predisposing mutation, LOH often affected the mutant allele in EC from Mut2 and Mut3 carriers (6/19, 31.6%). MLH1 promoter methylation, which reflected a more widespread hypermethylation tendency, occurred in 4/55 (7.3%) of tumors and was inversely associated with LOH. In conclusion, the patterns of somatic events (LOH and promoter methylation) differ depending on the tissue and germline mutation, which may in part explain the differential tumor susceptibility of different organs in HNPCC. MALDI-TOF provides a novel approach for the detection and quantification of LOH.

Accurate skin dose measurements using radiochromic film in clinical applications.

Megavoltage x-ray beams exhibit the well-known phenomena of dose buildup within the first few millimeters of the incident phantom surface, or the skin. Results of the surface dose measurements, however, depend vastly on the measurement technique employed. Our goal in this study was to determine a correction procedure in order to obtain an accurate skin dose estimate at the clinically relevant depth based on radiochromic film measurements. To illustrate this correction, we have used as a reference point a depth of 70 micron. We used the new GAFCHROMIC dosimetry films (HS, XR-T, and EBT) that have effective points of measurement at depths slightly larger than 70 micron. In addition to films, we also used an Attix parallel-plate chamber and a home-built extrapolation chamber to cover tissue-equivalent depths in the range from 4 micron to 1 mm of water-equivalent depth. Our measurements suggest that within the first millimeter of the skin region, the PDD for a 6 MV photon beam and field size of 10 x 10 cm2 increases from 14% to 43%. For the three GAFCHROMIC dosimetry film models, the 6 MV beam entrance skin dose measurement corrections due to their effective point of measurement are as follows: 15% for the EBT, 15% for the HS, and 16% for the XR-T model GAFCHROMIC films. The correction factors for the exit skin dose due to the build-down region are negligible. There is a small field size dependence for the entrance skin dose correction factor when using the EBT GAFCHROMIC film model. Finally, a procedure that uses EBT model GAFCHROMIC film for an accurate measurement of the skin dose in a parallel-opposed pair 6 MV photon beam arrangement is described.

Human brain wave activity during exposure to radiofrequency field emissions from mobile phones.

The aim of this study was to determine whether there is an effect of mobile phone electromagnetic field emissions on the human electroencephalograph (EEG). EEG recordings from ten awake subjects were taken during exposure to radiofrequency (RF) emissions from a mobile phone positioned behind the head. Two experimental trials were conducted. In the first trial, RF exposures were generated by a GSM mobile phone with the speaker disabled and configured to transmit at full-radiated power. During the second trial, exposures were generated by a non-modified GSM mobile phone in active standby mode. For each trial, subjects were exposed in five minute intervals to a randomized, interrupted sequence of five active and five sham exposures. The experiment was conducted under single-blind conditions. The average EEG band power in active exposure recordings was compared to corresponding sham recordings. Statistical tests indicated significant difference in the full-power mode trial within the EEG alpha (8-13 Hz) and beta (13-32 Hz) bands. A subsequent statistical analysis of median spectral power in discrete EEG rhythms revealed significant differences in 7 of the 32 distinct frequencies overall. In conclusion, the results of this study lend support to EEG effects from mobile phones activated in talk-mode.

Spectral karyotyping suggests additional subsets of colorectal cancers characterized by pattern of chromosome rearrangement.

The abundant chromosome abnormalities in most carcinomas are probably a reflection of genomic instability present in the tumor, so the pattern and variability of chromosome abnormalities will reflect the mechanism of instability combined with the effects of selection. Chromosome rearrangement was investigated in 17 colorectal carcinoma-derived cell lines. Comparative genomic hybridization showed that the chromosome changes were representative of those found in primary tumors. Spectral karyotyping (SKY) showed that translocations were very varied and mostly unbalanced, with no translocation occurring in more than three lines. At least three karyotype patterns could be distinguished. Some lines had few chromosome abnormalities: they all showed microsatellite instability, the replication error (RER)+ phenotype. Most lines had many chromosome abnormalities: at least seven showed a surprisingly consistent pattern, characterized by multiple unbalanced translocations and intermetaphase variation, with chromosome numbers around triploid, 6-16 structural aberrations, and similarities in gains and losses. Almost all of these were RER-, but one, LS411, was RER+. The line HCA7 showed a novel pattern, suggesting a third kind of genomic instability: multiple reciprocal translocations, with little numerical change or variability. This line was also RER+. The coexistence in one tumor of two kinds of genomic instability is to be expected if the underlying defects are selected for in tumor evolution.

Role of BAX mutations in mismatch repair-deficient colorectal carcinogenesis.

BAX gene mutations occur in approximately 50% of RER+ colorectal cancers. To determine the role of these mutations in tumour progression we analysed multiple different tumour sites from RER+ colorectal cancers for BAX mutations. Sixty colorectal carcinomas were analysed for microsatellite instability at loci BAT-26, L-myc, TGF betaRII, D13S160 and D2S123. Twelve out of 60 tumours (20%) were RER+. Forty-five different tumour sites from the 12 RER+ carcinomas were analysed for BAX mutations at the [(G)8] tract in exon 3. Six out of 12 (50%) RER+ tumours showed BAX mutations, four of which showed a homogenous pattern of such mutations detected in all tumour sites. In the other two cases, BAX mutations were present in some but not all tumour sites sampled from the same patient. In contrast, TGF betaRII mutations were found in 9/12 cases (75%) and in each of these were present in all the sampled sites. Two cases showed neither BAX nor TGF betaRII mutation. These data suggest that mutations in TGF betaRII may occur at a very early stage in tumour progression, perhaps in the founder clone. BAX mutations, however, are clearly not necessary for formation of the founder clone and can occur for the first time later in tumour progression.