Managing RT Schedules of Early-Stage Breast Cancer Patients with a Genetic-Dosimetric Validated Model for Late Fibrosis

PURPOSE/OBJECTIVE(S)

Define a multifactorial risk prediction model for RT-induced fibrosis and investigate the benefit of a personalized approach for breast cancer (BC) patients (pts) treated with whole breast RT.

MATERIALS/METHODS

In a previous study, we confirmed the predictive role of 30 SNPs from the literature and built an interaction aware Polygenic Risk Score (PRS, following the methods from Franco RO 2021) for Late Fibrosis (FG2+) on a cohort of 1500 pts from the REQUITE EU/USA prospective observational study. The PRS weights the radiosensitive (RS) and radioresistant (RR) genetic components and can be included in NTCP models. In a subgroup from the same cohort (390 pts), we have also confirmed an NTCP model based on biologically Equivalent Uniform Dose (BEUD) from PTV DVHs for pts treated at 40-50 Gy and no RT boost. Here, we combine PRS and BEUD into a sigmoid model allowing PRS to modulate BEUD50 (BEUD leading to 50% FG2+), i.e., we permitted a personalized BEUD50. We can also consider this as translating the PRS into a personalized equivalent BEUD, which is added/subtracted to the treatment BEUD. We evaluated model performances through ROC-AUC, calibration plot and Precision-Recall AUC.

RESULTS

A total of 381 pts had complete dosimetric/genetic data, prescribed dose 40-50 Gy, and no fibrotic alteration at RT start. We scored FG2+ in 87 pts (23%). PRS ranged from -13 (more RR pts) to 7 (more RS), and a unit in PRS corresponds to 5.3 Gy BEUD or 3 Gy in EQ EUD2 Gy. Table 1 summarizes model performances, with details for subgroups below/above the quartiles I/III of the BEUD distribution. The PRS-only model correctly describes the toxicity rates in the whole population (calibration slope/offset = 0/1). Still, it overestimates/underestimates the absolute risks in the low/high dose ranges. The integrated model improves AUC-ROC and AUC-PRC by 5% and 10% and guarantees a better calibration in pts receiving low/high BEUD to the PTV.

CONCLUSION

We developed a multifactorial model for FG2+ based on two previously validated models and reported the improvement against single-factor models. The BEUD+PRS model is suitable for assisting clinicians in managing early-stage BC pts. The number of fractions or the daily dose could be reduced for RS pts. The integrated model resulted in a possible quantitative tool for driving the planning decision process. Also, it showed a better performance in the high BEUD region, suggesting the potential value of its extension toward RT including boost or ultra hypofractionation. We are testing this extension in the whole REQUITE cohort.

Abstract S2-03: Does BRCA status affect outcome in young breast cancer patients? Results from the prospective study of outcomes in sporadic and hereditary breast cancer (POSH)

Background

Germline mutations in BRCA1/2 account for ∼3% of breast cancer cases but >10% of young patients who present with triple negative (TN) breast cancer. Young age at diagnosis is also associated with an increased risk of recurrence and inferior survival compared to older patients. Numerous publications describe an increased incidence of adverse biological features in tumours from young breast cancer patients; however it is unclear whether these fully explain the poor outcome.

The effect of carrying a BRCA1/2 mutation on the prognosis of breast cancer remains controversial with retrospective studies reporting better, similar and worse outcomes for mutation carriers compared to patients with sporadic tumours. BRCA carriers could feasibly have enhanced or reduced sensitivity to certain chemotherapeutics; however retrospective studies are problematic due to missing data and biased ascertainment. POSH is multicentre prospective observational cohort study designed to investigate factors which affect prognosis in young breast cancer patients (Copson et al, JNCI, 2013). Here we report the pathology, treatment and outcome of patients with TN tumours as a preliminary analysis to determine the impact of a germline BRCA1 mutation on survival. The whole cohort analysis including BRCA1 and BRCA2 is in progress.

Methods

2956 patients aged ≤40 at breast cancer diagnosis were recruited from 127 UK oncology centres between 2000 and 2008. Patient characteristics, family history, risk factors, tumour pathology and treatment information, and blood DNA were collected at recruitment. Follow-up data were collected at 6 and 12 months, then annually. Summary statistics were used to describe patients by BRCA1 status. Kaplan-Meier estimates were used to describe univariate survival data.

Results

BRCA1 status is currently available for 542 patients with TN tumours. Pathogenic BRCA1 mutations were identified in 122 patients (BRCA1+); 420 had no BRCA1 mutation (BRCA1-). BRCA1+ were younger than BRCA1- (median age 34 vs 36 years, p<0.001) and more likely to have a positive family history (p<0.001). There were no significant differences between BRCA1+ vs BRCA1- for: median tumour size (20.8mm vs 23.0mm); tumour grade distribution (95.8% grade 3 vs 93.6%); nodal involvement (35.2% node positive vs 39.9%); or presence of metastases at diagnosis (0.0% vs 1.0%).

Median follow-up was 7.3 years. Overall survival of patients with stage 1-3 disease treated with anthracycline +/- taxane neoadjuvant chemotherapy (n=538; 151 deaths) was better for BRCA1+ vs BRCA1- (79.1% vs 73.6% at 5-yrs; HR[95%CI]=0.84[0.57,1.25],p=0.388). Distant disease-free survival (DDFS) was also higher for BRCA1+ (5-yr DDFS 76.1% vs 71.5%; HR[CI]=0.92[0.63,1.35], p=0.682). Moreover, survival after first distant relapse was better for BRCA1+ patients (41.9% vs 36.8% at 1-yr; HR[CI]=0.78[0.51,1.18], p=0.233).

Conclusions

Our prospective data show better survival in young BRCA1+ patients with early TN breast cancer treated with anthracycline/-taxane chemotherapy than BRCA1- patients. However, the difference between the groups was not significant in this partial sample. Results for the whole cohort will be available by the time of the meeting.

Citation Format: Eccles DM, Copson ER, Maishman T, Tapper W, Cutress R, Gerty S, Stanton L, Altman DG, Durcan L, Simmonds P, Decker B, Allen J, Luccarini C, Easton D, Dunning A, POSH Steering Group and Collaborators. Does BRCA status affect outcome in young breast cancer patients? Results from the prospective study of outcomes in sporadic and hereditary breast cancer (POSH) [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr S2-03.

Quantitative apparent diffusion coefficient (ADC) values as an imaging biomarker for fibrosis in pediatric Crohn's disease: preliminary experience

PURPOSE

To compare histopathology with ADC values in strictured bowel segments in pediatric patients with known Crohn's disease and surgical bowel resection.

METHODS

Magnetic resonance enterography (MRE) images of 14 subjects with Crohn's disease who had surgical bowel resection for strictures were retrospectively reviewed. Five of 14 subjects had DWI (b=0, 500, 1000) sequences included in the MRE study. ADC measurements were made by placing ROI's in the strictured bowel wall and compared to full-thickness histologic analysis of resected specimens. ADC values were also compared to control ADC measurements (in normal and inflamed-nonstenotic bowel segments) as well as the mean ADC values of Crohn's patients published in the literature.

RESULTS

All five subjects had transmural fibrosis. The mean ADC value with b = 500 was 0.92 ± 0.10 × 10(-3) mm(2)/s and with b = 1000 was 0.8 ± 0.05 × 10(-3) mm(2)/s. There was a significant difference in ADC values between strictures and inflamed-nonstenotic segments (p=0.0143) and between normal and diseased bowel segments (p=0.009-0.0143).

CONCLUSIONS

Quantitative ADC measures of transmural fibrosis are lower compared to the reported values of inflammation in Crohn's disease. To our knowledge, this is the first pediatric pilot study to investigate the correlation of quantitative DWI with histology of surgical specimens in pediatric patients with Crohn's disease. Our results are comparable to a recently published study in adult Crohn's patients showing a significant correlation between a decrease in ADC values and fibrosis.

CD4 deficit and tuberculosis risk persist with delayed antiretroviral therapy: 5-year data from CIPRA HT-001

SETTING

Port-au-Prince, Haiti.

OBJECTIVE

To determine long-term effects of early vs. delayed initiation of antiretroviral therapy (ART) on immune recovery and tuberculosis (TB) risk in human immunodeficiency virus (HIV) infected individuals.

DESIGN

Open-label randomized controlled trial of immediate ART in HIV-infected adults with CD4 counts between 200 and 350 cells/mm(3) vs. deferring ART until the CD4 count was <200 cells/mm(3). The primary comparisons were CD4 counts over time and risk for incident TB, with 5 years of follow-up.

RESULTS

A total of 816 participants were enrolled, with 408 in each treatment arm. The early treatment group started ART within 2 weeks, while the deferred treatment group started ART a median of 1.3 years after enrollment. After 5 years, the mean CD4 count in the early treatment group was significantly higher than in the deferred treatment group (496 cells/mm(3), 95% confidence interval [CI] 477-515 vs. 373 cells/mm(3), 95%CI 357-389; P < 0.0001). TB risk was higher in the deferred treatment group (unadjusted HR 2.41, 95%CI 1.56-3.74; P < 0.0001) and strongly correlated with lower CD4 counts in time-dependent multivariate analysis.

CONCLUSION

Delays in ART initiation for HIV-infected adults with CD4 counts of 200-350 cells/mm(3) can result in long-term immune dysfunction and persistent increased risk for TB.

CT perfusion for detection of delayed cerebral ischemia in aneurysmal subarachnoid hemorrhage: a systematic review and meta-analysis

BACKGROUND AND PURPOSE

Delayed cerebral ischemia is a significant cause of morbidity and mortality after aneurysmal SAH, leading to poor outcomes. The purpose of this study was to evaluate the usefulness of CTP in determining delayed cerebral ischemia in patients with aneurysmal SAH.

MATERIALS AND METHODS

We conducted a systematic review evaluating studies that assessed CTP in patients with aneurysmal SAH for determining delayed cerebral ischemia. Studies using any of the following definitions of delayed cerebral ischemia were included in the systematic review: 1) new onset of clinical deterioration, 2) cerebral infarction identified on follow-up CT or MR imaging, and 3) functional disability. A random-effects meta-analysis was performed assessing the strength of association between a positive CTP result and delayed cerebral ischemia.

RESULTS

The systematic review identified 218 studies that met our screening criteria, of which 6 cohort studies met the inclusion criteria. These studies encompassed a total of 345 patients, with 155 (45%) of 345 patients classified as having delayed cerebral ischemia and 190 (55%) of 345 patients as not having delayed cerebral ischemia. Admission disease severity was comparable across all groups. Four cohort studies reported CTP test characteristics amenable to the meta-analysis. The weighted averages and ranges of the pooled sensitivity and specificity of CTP in the determination of delayed cerebral ischemia were 0.84 (0.7-0.95) and 0.77 (0.66-0.82), respectively. The pooled odds ratio of 23.14 (95% CI, 5.87-91.19) indicates that patients with aneurysmal SAH with positive CTP test results were approximately 23 times more likely to experience delayed cerebral ischemia compared with patients with negative CTP test results.

CONCLUSIONS

Perfusion deficits on CTP are a significant finding in determining delayed cerebral ischemia in aneurysmal SAH. This may be helpful in identifying patients with delayed cerebral ischemia before development of infarction and neurologic deficits.

Intraplaque high-intensity signal on 3D time-of-flight MR angiography is strongly associated with symptomatic carotid artery stenosis

BACKGROUND AND PURPOSE

Intraplaque hemorrhage in carotid artery atherosclerotic plaque has been shown to be a marker of risk, associated with prior and future ischemic events, and has been associated with regions of intraplaque high-intensity signal on 3D-TOF MRA. We assessed the association of intraplaque high-intensity signal determined on 3D-TOF MRA with the incidence of prior ipsilateral stroke or TIA.

MATERIALS AND METHODS

We assessed intraplaque hemorrhage by evaluating for intraplaque high-intensity signal adapting a recently validated technique on 3D-TOF source images in participants with high-grade (≥ 70%) extracranial carotid stenosis. Logistic regression analyses were used to assess the strength of association between the presence of intraplaque high-intensity signal on routine MRA sequences and prior stroke or TIA.

RESULTS

Intraplaque high-intensity signal was present in 22 (41.5%) of 53 carotid arteries studied in 51 patients. Ipsilateral ischemic events occurred in 15 (68.1%) of 22 in the intraplaque high-intensity signal-positive group (10 strokes, 5 TIAs) and in 4 (12.9%) of 31 in the intraplaque high-intensity signal-negative group (3 strokes, 1 TIA). Ischemic events occurred within the 6-month period preceding imaging in 18 (94.7%) of 19 cases. The univariate odds ratio of the association of intraplaque high-intensity signal with any prior ischemic event was 14.5 (95% CI, 3.6-57.6), and the multivariate age- and sex-adjusted odds ratio was 14.2 (95% CI, 3.3-60.5). The association remained present across 1.5 T and 3T magnet field strengths.

CONCLUSIONS

Intraplaque high-intensity signal determined from MRA sequences already in place to measure luminal stenosis is strongly associated with prior ipsilateral ischemic events. Prospective validation of these findings to predict outcome in carotid artery stenosis could provide a valuable and widely accessible stroke risk stratification tool.

Functional variants at the 11q13 risk locus for breast cancer regulate cyclin D1 expression through long-range enhancers

Analysis of 4,405 variants in 89,050 European subjects from 41 case-control studies identified three independent association signals for estrogen-receptor-positive tumors at 11q13. The strongest signal maps to a transcriptional enhancer element in which the G allele of the best candidate causative variant rs554219 increases risk of breast cancer, reduces both binding of ELK4 transcription factor and luciferase activity in reporter assays, and may be associated with low cyclin D1 protein levels in tumors. Another candidate variant, rs78540526, lies in the same enhancer element. Risk association signal 2, rs75915166, creates a GATA3 binding site within a silencer element. Chromatin conformation studies demonstrate that these enhancer and silencer elements interact with each other and with their likely target gene, CCND1.

Decreased breast cancer risk in systemic lupus erythematosus: the search for a genetic basis continues

PURPOSE

Recent work has demonstrated an important decrease in breast cancers for women with systemic lupus erythematosus (SLE). The reason behind this phenomenon is unknown. Our purpose was to explore whether the single nucleotide polymorphisms (SNPs) predisposing to SLE might be protective against breast cancer (in women in the general population).

METHODS

We focused on loci relevant to 10 SNPs associated with SLE (with a p value of <10(-9)). We determined whether we could establish a decreased frequency of these SNPs in breast cancer cases versus controls, within the general population. To do this we used a large breast cancer genome-wide association study (GWAS) dataset, involving 3,659 breast cancer cases and 4,897 controls. These subjects were all primarily of European ancestry.

RESULTS

The population-based GWAS breast cancer data we examined suggested little evidence for important associations between breast cancer and SLE-related SNPs. Within the general population GWAS data, a cytosine(C) nucleotide substitution at rs9888739 (on chromosome 16p11.2) showed a very weak inverse association with breast cancer. The odds ratio (OR) for the rs9888739-C allele was 0.907551 (p value 0.049899) in the GWAS breast cancer sample, compared to controls. There was a slightly stronger, positive, association with breast cancer for rs6445975-G (Guanine) on chromosome 3p14.3, with a breast cancer OR of 1.0911 (p value 0.0097).

CONCLUSIONS

Within this large breast cancer dataset, we did not demonstrate important associations with 10 lupus-associated SNPs. If decreased breast cancer risk in SLE is influenced by genetic profiles, this may be due to complex interactions and/or epigenetic factors.

Diagnostic accuracy of 4D-CT for parathyroid adenomas and hyperplasia

BACKGROUND AND PURPOSE

4D-CT is a novel method of multiphase CT imaging. When used to localize parathyroid adenomas and hyperplasia, this technique may allow for more robust diagnostic accuracy than traditional sonography and nuclear scintigraphy techniques. The purpose of our study is to assess the accuracy of 4D-CT for localizing pathologically proved parathyroid adenomas and hyperplasia found during surgery.

MATERIALS AND METHODS

A total of 35 pathologically proved cases of parathyroid adenoma and hyperplasia were retrospectively reviewed between January 2009 and March 2011. Inclusion criteria were availability of final surgical pathology and performance of preoperative 4D-CT. No cases were excluded. Sensitivity, specificity, and accuracy of 4D-CT were ascertained including both the side and quadrant of the pathologically proved lesion.

RESULTS

Of the 35 pathologically proved cases collected over the study period, 32 (sensitivity = 91%) patients were found positive for parathyroid disease using 4D-CT, including 3 cases of multigland disease. For lateralization of single-gland disease, 4D-CT demonstrated an accuracy of 93%. 4D-CT revealed a suboptimal 44% sensitivity, but 100% specificity, for multigland disease.

CONCLUSIONS

4D-CT demonstrated a high diagnostic accuracy for single and multigland disease in our cohort. Importantly, 4D-CT accurately lateralized single-gland adenomas in >90% of cases, allowing the surgeon to employ a directed operative approach. 4D-CT also showed a very high specificity for the detection of multigland disease.

Prognostic factors of cancer recurrence and progression in non-muscle-invasive urothelial carcinoma: A multicenter study of over 4,300 patients

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Background: The outcomes of patients with non-muscle-invasive urothelial carcinoma of the bladder (NMIUCB) remain poorly understood. The aim of our study was to identify prognostic factors of cancer recurrence and progression in patients with primary UCB.

Methods: We performed a combined analysis on individual data from 4,325 patients with primary NMIUCB.

Results: Within a median follow-up of 64 months, 1,960 patients (45.4%) experienced disease recurrence, 498 (11.5%) experienced progression to muscle-invasive stage, 1,155 (26.7%) died of any cause, and 310 (7.2%) died of their cancer. In multivariable Cox regression analysis, advanced age, higher grade, larger tumor size, higher number of tumors, number of prior recurrences, and type of intravesical therapy were independent predictors of disease recurrence and progression. While treatment intravesical chemotherapy was only associated with decreased/delayed cancer recurrence, intravesical BCG therapy was associated with decreased/delayed cancer recurrence and progression. The predictive accuracies of the models for recurrence and progression were 63.5% and 71.3%, respectively.

Conclusions: Even in a heterogenous patient population, BCG therapy appears to decrease frequency and delay time to cancer recurrence and progression in patients with NMIUCB. Predictive tools based on combination of multiple clinical variables which capture the biological and clinical potential of nonmuscle-invasive disease could help with patient counseling and individualized risk assessment for adjuvant intravesical therapy and clinical trial design.

[Table: see text]

No significant financial relationships to disclose.

Genetic susceptibility according to three metabolic pathways in cancers of the lung and bladder and in myeloid leukemias in nonsmokers

BACKGROUND

We chose a set of candidate single nucleotide polymorphisms (SNPs) to investigate gene-environment interactions in three types of cancer that have been related to air pollution (lung, bladder and myeloid leukemia).

PATIENTS AND METHODS

The study has been conducted as a nested case-control study within the European Prospective Investigation into Cancer and Nutrition cohort (409 cancer cases and 757 matched controls). We included never and ex-smokers. SNPs were in genes involved in oxidative stress, phase I metabolizing genes, phase II metabolizing genes and methylenetetrahydrofolate reductase (MTHFR).

RESULTS

The most notable findings are: GSTM1 deletion and bladder cancer risk [odds ratio (OR) = 1.60; 95% confidence interval 1.00-2.56]; CYP1A1 and leukemia (2.22, 1.33-3.70; heterozygotes); CYP1B1 and leukemia (0.47, 0.27-0.84; homozygotes); MnSOD and leukemia (1.91, 1.08-3.38; homozygotes) and NQO1 and lung cancer (8.03, 1.73-37.3; homozygotes). Other statistically significant associations were found in subgroups defined by smoking habits (never or ex-smokers), environmental tobacco smoke or gender, with no obvious pattern. When gene variants were organized according to the three main pathways, the emerging picture was of a strong involvement of combined phase I enzymes in leukemia, with an OR of 5 (1.63-15.4) for those having three or more variant alleles. The association was considerably stronger for leukemias arising before the age of 55.

HapMap-based study of the 17q21 ERBB2 amplicon in susceptibility to breast cancer

ERBB2 is frequently amplified in breast tumours as part of a wide region of amplification on chromosome 17q21. This amplicon contains many candidate genes for breast cancer susceptibility. We used a genetic association study design to determine if common genetic variation (frequency>or=5%) in a 400-kb region surrounding ERBB2 and containing the PPARBP, CRK7, NEUROD2, PPP1R1B, STARD3, TCAP, PNMT, CAB2, ERBB2, C17ORF37, GRB7 and ZNFN1A3 genes, was associated with breast cancer risk. Sixteen tagging single-nucleotide polymorphisms (tSNPs) selected within blocks of linkage disequilibrium from the HapMap database, one HapMap singleton SNP, and six additional SNPs randomly selected from dbSNP were genotyped using Taqman in a large study set of British women (2275 cases, 2280 controls). We observed no association between any of the genotypes or associated haplotypes and disease risk. In order to simulate unidentified SNPs, we performed the leave-one-out cross-validation procedure on the HapMap data; over 90% of the common genetic variation was well represented by tagging polymorphisms. We are therefore likely to have tagged any common variants present in our population. In summary, we found no association between common genetic variation in the 17q21 ERBB2 amplicon and breast cancer risk in British women.

Methodology of laboratory measurements in prospective studies on gene-environment interactions: the experience of GenAir

Several large prospective investigations are under way or are planned in different parts of the world, aiming at the investigation of gene-environment interactions for chronic diseases. Technical, practical and ethical issues are raised by such large investigations. Here we describe how such issues were approached within a case-control study nested in EPIC, a large European cohort, and the kind of validation studies that have been set up. The GenAir investigation aimed at measuring the effects of air pollution and environmental tobacco smoke on human health in EPIC with a nested design and with biological measures. Validation studies included (a) comparisons between cotinine measurements, hemoglobin adducts and questionnaire data; (b) an analysis of the determinants of DNA adduct concentration; (c) comparison among different genotyping methods; (d) an analysis of the determinants of plasma DNA amounts. We also describe how the ethical issues were dealt with in our investigation.

Environmental tobacco smoke and risk of respiratory cancer and chronic obstructive pulmonary disease in former smokers and never smokers in the EPIC prospective study

OBJECTIVES

To investigate the association between environmental tobacco smoke, plasma cotinine concentration, and respiratory cancer or death.

DESIGN

Nested case-control study within the European prospective investigation into cancer and nutrition (EPIC).

PARTICIPANTS

303,020 people from the EPIC cohort (total 500,000) who had never smoked or who had stopped smoking for at least 10 years, 123,479 of whom provided information on exposure to environmental tobacco smoke. Cases were people who developed respiratory cancers or died from respiratory conditions. Controls were matched for sex, age (plus or minus 5 years), smoking status, country of recruitment, and time elapsed since recruitment.

MAIN OUTCOME MEASURES

Newly diagnosed cancer of lung, pharynx, and larynx; deaths from chronic obstructive pulmonary disease or emphysema. Plasma cotinine concentration was measured in 1574 people.

RESULTS

Over seven years of follow up, 97 people had newly diagnosed lung cancer, 20 had upper respiratory cancers (pharynx, larynx), and 14 died from chronic obstructive pulmonary disease or emphysema. In the whole cohort exposure to environmental tobacco smoke was associated with increased risks (hazard ratio 1.30, 95% confidence interval 0.87 to 1.95, for all respiratory diseases; 1.34, 0.85 to 2.13, for lung cancer alone). Higher results were found in the nested case-control study (odds ratio 1.70, 1.02 to 2.82, for respiratory diseases; 1.76, 0.96 to 3.23, for lung cancer alone). Odds ratios were consistently higher in former smokers than in those who had never smoked; the association was limited to exposure related to work. Cotinine concentration was clearly associated with self reported exposure (3.30, 2.07 to 5.23, for detectable/non-detectable cotinine), but it was not associated with the risk of respiratory diseases or lung cancer. Frequent exposure to environmental tobacco smoke during childhood was associated with lung cancer in adulthood (hazard ratio 3.63, 1.19 to 11.11, for daily exposure for many hours).

CONCLUSIONS

This large prospective study, in which the smoking status was supported by cotinine measurements, confirms that environmental tobacco smoke is a risk factor for lung cancer and other respiratory diseases, particularly in ex-smokers.

Polygenic inherited predisposition to breast cancer

The known breast cancer predisposing genes account for only about 20% of inherited susceptibility. Epidemiological analyses suggest that much of the remaining 80% is explained by the combined effect of many individually weak genetic variants, rather than by further rare, highly penetrant mutations. In the near term, identification of variants may indicate new pathways or mechanisms in breast cancer development. The polygenic model implies a wide distribution of risk in the population. In the longer term, it may be possible to construct individual risk profiles to guide public health interventions. The search for genetic variants has so far proved difficult. A key unanswered question is the "genetic architecture" of predisposition-that is, strong or weak alleles, common or rare. We describe a genome-wide scan designed to provide a first-pass answer to this question.

The amino terminus of apolipoprotein B is necessary but not sufficient for microsomal triglyceride transfer protein responsiveness

Human apolipoprotein (apo) B mediates the formation of neutral lipid-containing lipoproteins in the liver and intestine. The association of apoB with lipid is thought to be promoted by the microsomal triglyceride transfer protein complex. We have reconstituted lipoprotein assembly in an insect cell line that normally does not support this process. Expression of human microsomal triglyceride transfer protein (MTP) and apolipoprotein B48 (apoB48) together enabled Sf-21 insect cells to secrete approximately 60-fold more lipoprotein-associated triacylglycerol than control cells. This dramatic effect demonstrates that effective partitioning of triacylglycerol into the secretory pathway requires an endoplasmic reticulum-associated neutral lipid transporter (provided by MTP) and an apolipoprotein to shuttle the lipid through the pathway. Expression of the human apoB48 gene in insect cells resulted in secretion of the protein product. Including both MTP subunits with apoB48 and oleic acid specifically increased apoB48 secretion 8-fold over individual subunits alone. To assess whether specific regions of apoB are necessary for MTP responsiveness, nine apoB segments were expressed. These included NH2-terminal segments as well as internal and COOH-terminal regions of apoB fused with a heterologous signal sequence. ApoB segments containing the NH2-terminal 17% of the protein were secreted and responded to MTP activity; however, a segment containing only the NH2-terminal 17% of the protein was not significantly responsive to MTP. Segments lacking the NH2 terminus were not MTP-responsive, and five of six of these proteins were trapped intracellularly but, in certain cases, could be rescued by fusion to apoB17. These results suggest that the NH2 terminus of apoB is necessary but not sufficient for MTP responsiveness.

A gene (DLG2) located at 17q12-q21 encodes a new homologue of the Drosophila tumor suppressor dIg-A

We have isolated a novel cDNA that maps distal to BRCA1 at 17q12-q21. The total sequence predicts a protein of 576 amino acids with three conserved regions: a 90-amino-acid repeat domain, a SH3 (src homology region 3) motif, and a guanylate kinase domain. These conserved regions are shared among members of the discs-large family of proteins that include human p55, a membrane protein expressed in erythrocytes, rat PSD-95/SAP90, a synapse protein expressed in brain, Drosophila dIg-A, a septate junction protein expressed in various epithelia, and human and mouse ZO-1 and canine ZO-2, two tight junction proteins. dIg-A has been shown to act as a tumor suppressor, and the other members may all be involved in signal transduction through specialized membrane domains with highly organized cytoskeletons and thus are potential tumor suppressors. Since allelic loss has been reported in the 17q12-q21 region in breast and ovarian cancer and it appears that BRCA1 is not the target of the losses, we looked for somatic alterations in DLG2 in sporadic breast tumors. No evidence for mutation was found, making it unlikely that DLG2 is involved in sporadic breast cancer.

Three-field breast irradiation technique using tangential quarter fields

We have developed and implemented in clinical practice an isocentric three-field breast irradiation technique using tangential quarter fields. In this technique, the same isocenter is used for the supraclavicular and the tangential breast fields. The superior-posterior corner of the tangential breast fields is placed at the central axis by asymmetric collimation of both the length and the width of the field. Consequently, the beam divergence at both the superior and posterior edges is eliminated, allowing a perfect geometric match between the posterior borders of both tangential breast fields and the supraclavicular field without table rotation. Compared to conventional techniques requiring table rotations, the present method produces a more uniform dose distribution in the target volume and requires significantly less simulation time.

DNA polymorphism studies. Approaches to elucidating multifactorial ischaemic heart disease: the apo B gene as an example

It is well established that elevated plasma levels of low-density lipoprotein (LDL) particles are a risk factor for ischaemic heart disease with the distribution in LDL levels seen in the general population being the result of interaction between environmental factors, such as dietary fat intake, and genetic variation that is present in different individuals. One of the candidate genes where such variation is likely to occur, is the gene coding for apolipoprotein B (apo B). Many studies have reported an association between a common polymorphism of the apo B gene, detected using the restriction enzyme XbaI, and differences in plasma lipid levels, explaining 3-5% of the variance in LDL-cholesterol levels in samples representative of the healthy population. It has been proposed that the mechanism of this association is due to functional amino acid changes within the apo B protein, that affect LDL catabolism by altering binding affinity to the LDL-receptor. Several amino acid substitutions in the apo B gene have now been characterized, and these form the basis of the different epitopes that create the Ag marker system. Previous studies have reported that the Ag(x) epitope is associated with lower plasma lipid levels, and until recently the molecular basis for this association has been unclear. We have determined that the Ag(x) epitope is associated with both a Pro-Leu2712, and Asn-Ser4311 substitution, with the Leu-Ser allele being associated with significantly lower levels of plasma lipids in a sample of healthy individuals from Sweden.(ABSTRACT TRUNCATED AT 250 WORDS)

Apolipoprotein B gene polymorphisms, lipoproteins and coronary atherosclerosis: a study of young myocardial infarction survivors and healthy population-based individuals

Association studies were carried out in a sample of 87 patients from Sweden who had survived a myocardial infarction (MI) before the age of 45, and 91 age-matched healthy individuals, to compare the impact of polymorphisms at the apolipoprotein (apo) E and B gene loci on among-individual differences in plasma lipid traits and progression of atherosclerosis. In the group of healthy individuals, polymorphisms creating the common apo E isoforms were, as expected, associated with significant differences in total and low density lipoprotein (LDL) cholesterol (11.7% and 11.6% of sample variance). For apo B, the polymorphism with the largest effect on apo B levels (16% of sample variance) was the C to T transition 265 bp 5' of the cap site, in the promoter (detectable by MspI). Both this polymorphism and the threonine2488 neutral substitution (detectable by XbaI) were associated with significant effects on LDL-cholesterol (8.3% and 9.3% of sample variance, respectively). The asparagine/serine4311 polymorphism was associated with a significant effect on high density lipoprotein (HDL) cholesterol alone, and there was no significant association with the glutamate/lysine4154 polymorphism (detectable by EcoRI) or the leucine-alanine-leucine (LAL) insertion/deletion polymorphism in the signal peptide. In the patients, polymorphisms creating the three common apo E isoforms were associated with large effects on cholesterol, apo B and triglyceride levels (19.9%, 20.3% and 23.9% of sample variance) of similar magnitude as in the healthy individuals. Apo B polymorphisms were found to be associated with much smaller effects on lipid traits than in the healthy individuals. The only significant association was between the asparagine/serine4311 polymorphism and HDL-triglyceride levels. However, global severity of coronary atherosclerosis at the first angiography was found to be significantly associated with the LAL insertion/deletion polymorphism (P = 0.008). Thus variation at the apo B gene locus is associated with the development of atherosclerosis, but the data suggests that this may act through mechanisms not directly related to effects on measured lipid traits.

A novel truncated apolipoprotein B (apo B55) in a patient with familial hypobetalipoproteinemia and atypical retinitis pigmentosa

We have identified an apolipoprotein (apo) B mutation in a patient with an atypical form of retinitis pigmentosa (RP). In the family the eye disease is characterised by late age of onset and autosomal dominant inheritance. In addition to RP, the proband has low total cholesterol (4.5 mmol/l) and LDL-cholesterol (2.0 mmol/l) levels characteristic of the autosomal codominant apolipoprotein (apo) B deficiency disease hypobetalipoproteinemia (HBL). Using a monoclonal antibody directly against apo B and immunoblots of SDS polyacrylamide gel separated plasma, a normal apo B100 and a truncated apo B species with an estimated size of apo B54 was identified in the proband and his RP-affected sister. The location of the mutation in the apo B gene was identified using chemical cleavage of mismatch and this was confirmed by direct sequencing of an amplified fragment of DNA spanning the estimated site of the mutation. The mutation is a C----T transition at nucleotide 7692 which changes the CGA arginine2495 codon to a STOP codon resulting in the premature termination of apo B100. The truncated apo B protein is 2494 amino acids long with a predicted size of apo B55. Using allele specific oligonucleotides and oligonucleotide melting techniques, the proband, his sister and two other relatives out of a total of 20 family members, screened for the presence of the apo B55 mutation, were heterozygous for the mutation. The segregation of the apo B55 allele was confirmed in the family using the 3' variable number of tandem repeats of the apo B gene.(ABSTRACT TRUNCATED AT 250 WORDS)

Gene probes in diagnosis of familial hypercholesterolemia

In the United Kingdom, about 5% of patients with familial hypercholesterolemia (FH) have a detectable deletion or rearrangement of part of the LDL-receptor gene, which results in the detection of shorter or abnormally sized fragments of the LDL-receptor gene in a Southern blot hybridization. This gene deletion can be used for following the inheritance of the defective gene and for diagnosis in the families of these individuals. In the families of the remaining patients, diagnosis may be possible using linked restriction fragment length polymorphisms (RFLPs) detected with the LDL-receptor probe. There are now 10 common RFLPs of the LDL-receptor gene, with variable sites in the 3' half of the gene. Over 80% of patients are heterozygous for at least one of these RFLPs, and, therefore, RFLPs are potentially informative for DNA diagnosis. For a fetus at risk of homozygous FH, antenatal diagnosis may also be possible using these methods. However, family studies require samples to be available from affected or unaffected relatives of the patient, and this limits the applicability of the tests. For some mutations, the base-pair change causing the defect in the LDL receptor itself creates or destroys a site for a restriction enzyme. Such "mutation-specific" RFLPs could be used for population screening, but, so far, such use has only been reported for the FH mutation common in Lebanon. In the future, it may be possible to develop mutation-specific oligonucleotide probes for the diagnosis of FH. These would be appropriate for screening populations or patients with hyperlipidemia. This information may also be useful if different mutations require different therapeutic strategies.

Unequal crossing-over between two alu-repetitive DNA sequences in the low-density-lipoprotein-receptor gene. A possible mechanism for the defect in a patient with familial hypercholesterolaemia

We have previously identified a patient with familial hypercholesterolaemia (FH), where the defect appears to be caused by a deletion in the 3' region of the low-density lipoprotein (LDL)-receptor gene. We have now isolated the LDL-receptor gene from the patient and have studied the defect at the DNA level. Restriction mapping and sequence analysis demonstrate that a 4-kb DNA deletion has occurred between two alu-repetitive sequences that are in the same orientation, one in intron 12 and the other in intron 14. This deletion eliminates exons 13 and 14, and changes the reading frame of the resulting spliced mRNA such that a stop codon is created in the following exon. Immuno- and ligand-blot analysis using cultured fibroblasts from this patient revealed the normal gene product, but failed to detect any smaller receptor protein. This implies that the truncated receptor protein that is synthesised is rapidly degraded. We suggest that in this patient the deletion is caused by an unequal crossing-over event that occurred between two homologous chromosomes at meiosis.

Identification of deletions in the human low density lipoprotein receptor gene

DNA samples from 70 unrelated UK patients with heterozygous familial hypercholesterolaemia were screened by Southern blot hybridisation with a 5' fragment of the human low density lipoprotein (LDL) receptor cDNA. In the majority of cases, the restriction fragment pattern of the LDL receptor gene was indistinguishable from that observed in normal subjects. However, three patients were found to have a deletion of approximately 1 kb in the central portion of the gene. Mapping experiments indicated that in two patients a similar deletion has occurred that includes all or part of exon 5, and in the third patient a deletion has occurred that includes exon 7. Taking into account our previously described patient with a deletion in the 3' part of the gene, this means that in four out of 70 UK patients with familial hypercholesterolaemia (6%), the defect is caused by a detectable deletion of part of the coding portion of the low density lipoprotein receptor gene.