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I Linkov

Publications and source records attributed to I Linkov.

At least 19 recordsLinked to original sources

Radionuclides in fruit systems: model prediction-experimental data intercomparison study.

This paper presents results from an international exercise undertaken to test model predictions against an independent data set for the transfer of radioactivity to fruit. Six models with various structures and complexity participated in this exercise. Predictions from these models were compared against independent experimental measurements on the transfer of 134Cs and 85Sr via leaf-to-fruit and soil-to-fruit in strawberry plants after an acute release. Foliar contamination was carried out through wet deposition on the plant at two different growing stages, anthesis and ripening, while soil contamination was effected at anthesis only. In the case of foliar contamination, predicted values are within the same order of magnitude as the measured values for both radionuclides, while in the case of soil contamination models tend to under-predict by up to three orders of magnitude for 134Cs, while differences for 85Sr are lower. Performance of models against experimental data is discussed together with the lessons learned from this exercise.

Cesium Radioisotopes↗

Multicriteria decision analysis: a comprehensive decision approach for management of contaminated sediments.

Contaminated sediments and other sites present a difficult challenge for environmental decisionmakers. They are typically slow to recover or attenuate naturally, may involve multiple regulatory agencies and stakeholder groups, and engender multiple toxicological and ecotoxicological risks. While environmental decision-making strategies over the last several decades have evolved into increasingly more sophisticated, information-intensive, and complex approaches, there remains considerable dissatisfaction among business, industry, and the public with existing management strategies. Consequently, contaminated sediments and materials are the subject of intense technology development, such as beneficial reuse or in situ treatment. However, current decision analysis approaches, such as comparative risk assessment, benefit-cost analysis, and life cycle assessment, do not offer a comprehensive approach for incorporating the varied types of information and multiple stakeholder and public views that must typically be brought to bear when new technologies are under consideration. Alternatively, multicriteria decision analysis (MCDA) offers a scientifically sound decision framework for management of contaminated materials or sites where stakeholder participation is of crucial concern and criteria such as economics, environmental impacts, safety, and risk cannot be easily condensed into simple monetary expressions. This article brings together a multidisciplinary review of existing decision-making approaches at regulatory agencies in the United States and Europe and synthesizes state-of-the-art research in MCDA methods applicable to the assessment of contaminated sediment management technologies. Additionally, it tests an MCDA approach for coupling expert judgment and stakeholder values in a hypothetical contaminated sediments management case study wherein MCDA is used as a tool for testing stakeholder responses to and improving expert assessment of innovative contaminated sediments technologies.

Journal Article↗

Radionuclides in fruit systems: model-model intercomparison study.

Modeling is widely used to predict radionuclide distribution following accidental radionuclide releases. Modeling is crucial in emergency response planning and risk communication, and understanding model uncertainty is important not only in conducting analysis consistent with current regulatory guidance, but also in gaining stakeholder and decision-maker trust in the process and confidence in the results. However, while methods for dealing with parameter uncertainty are fairly well developed, an adequate representation of uncertainties associated with models remains rare. This paper addresses uncertainty about a model's structure (i.e., the relevance of simplifying assumptions and mathematical equations) that is seldom addressed in practical applications of environmental modeling. The use of several alternative models to derive a range of model outputs or risks is probably the only available technique to assess consistency in model prediction. Since each independent model requires significant resources for development and calibration, multiple models are not generally applied to the same problem. This study uses results from one such model intercomparison conducted by the Fruits Working Group, which was created under the International Atomic Energy Agency (IAEA) BIOMASS (BIOsphere Modelling and ASSessment) Program. Model-model intercomparisons presented in this study were conducted by the working group for two different scenarios (acute or continuous deposition), one radionuclide ((137)Cs), and three fruit-bearing crops (strawberries, apples, and blackcurrants). The differences between models were as great as five orders of magnitude for short-term predictions following acute radionuclide deposition. For long-term predictions and for the continuous deposition scenario, the differences between models were about two orders of magnitude. The difference between strawberry, apple, and blackcurrant contamination predicted by one model is far less than the difference in prediction of contamination for a single plant species given by different models. This study illustrates the importance of problem formulation and implementation of an analytic-deliberative process in risk characterization.

Cesium Radioisotopes↗

Radionuclide migration in forest ecosystems--results of a model validation study.

The primary objective of the IAEA's BIOMASS Forest Working Group (FWG) was to bring together experimental radioecologists and modellers to facilitate the exchange of information which could be used to improve our ability to understand and forecast radionuclide transfers within forests. This paper describes a blind model validation exercise which was conducted by the FWG to test nine models which members of the group had developed in response to the need to predict the fate of radiocaesium in forests in Europe after the Chernobyl accident. The outcomes and conclusions of this exercise are summarised. It was concluded that, as a group, the models are capable of providing an envelope of predictions which can be expected to enclose experimental data for radiocaesium contamination in forests over the time scale tested. However, the models are subject to varying degrees of conceptual uncertainty which gives rise to a very high degree of divergence between individual model predictions, particularly when forecasting edible mushroom contamination. Furthermore, the forecasting capability of the models over future decades currently remains untested.

Ecosystem↗

Modelling and experimental studies on the transfer of radionuclides to fruit.

Although fruit is an important component of the diet, the extent to which it contributes to radiological exposure remains unclear, partially as a consequence of uncertainties in models and data used to assess transfer of radionuclides in the food chain. A Fruits Working Group operated as part of the IAEA BIOMASS (BIOsphere Modelling and ASSessment) programme from 1997 to 2000, with the aim of improving the robustness of the models that are used for radiological assessment. The Group completed a number of modelling and experimental activities including: (i) a review of experimental, field and modelling information on the transfer of radionuclides to fruit; (ii) discussion of recently completed or ongoing experimental studies; (iii) development of a database on the transfer of radionuclides to fruit; (iv) development of a conceptual model for fruit and (v) two model intercomparison studies and a model validation study. The Group achieved significant advances in understanding the processes involved in transfer of radionuclides to fruit. The work demonstrated that further experimental and modelling studies are required to ensure that the current generation of models can be applied to a wide range of scenarios.

Fruit↗

Equilibrium of radiocesium with stable cesium within the biological cycle of contaminated forest ecosystems.

Concentrations of (137)Cs and stable Cs were determined in plant, mushroom, lichen and soil samples collected at two forest sites with different contamination levels in Belarus in 1998. The concentration of (137)Cs in soil was the highest in near-surface organic layers (Of and Oh horizons) and decreased with depth in the mineral layers, whereas the concentrations of stable Cs were almost constant in the soil profile. The levels of (137)Cs and stable Cs in biological samples varied depending both on the species and the plant part sampled. Even though different species and parts of the same species were included, the concentration ratios of (137)Cs to stable Cs were fairly constant for samples collected at the same forest site, and were in the same order of magnitude as the (137)Cs to stable Cs ratios for the organic soil layers. This finding suggests that (137)Cs, mainly deposited on the forest ecosystems from the Chernobyl accident in 1986, was well mixed with stable Cs within the biological cycle in the forest ecosystems by 1998. The transfer factor for each biological sample of (137)Cs was almost the same as that of stable Cs, if they were calculated based on the concentrations in the Of + Oh layer. This suggests that the stable-Cs-based transfer factor could be used as equilibrium transfer factor of (137)Cs for different types of biological samples in the forest.

Agaricales↗

The role of fungi in the transfer and cycling of radionuclides in forest ecosystems.

Fungi are one of the most important components of forest ecosystems, since they determine to a large extent the fate and transport processes of radionuclides in forests. They play a key role in the mobilization, uptake and translocation of nutrients and are likely to contribute substantially to the long-term retention of radiocesium in organic horizons of forest soil. This paper gives an overview of the role of fungi regarding the transfer and cycling of nutrients and radionuclides, with special emphasis on mycorrhizal symbiosis. Common definitions of transfer factors, soil-fungus and soil-green plant, including their advantages and limitations. are reviewed. Experimental approaches to quantify the bioavailability of radionuclides in soil and potential long-term change are discussed.

Biological Availability↗

Uncertainty and variability in risk from trophic transfer of contaminants in dredged sediments.

The risks associated with bioaccumulative contaminants must be considered when evaluating dredged material disposal alternatives. The bioaccumulation of organochlorines and other contaminants by higher trophic level organisms represents one of the most significant sources of uncertainty in risk assessment. Both population variability (e.g. true population heterogeneity in body weight, lipid content, etc.) and uncertainty (e.g. measurement error) in trophic transfer can lead to large errors in predicted risk values for ecological receptors. This paper describes and quantitatively evaluates sources of uncertainty and variability in estimating the risk to an ecological receptor (osprey) from the trophic transfer of polychlorinated biphenyls (PCBs) in sediments from the New York-New Jersey (NY-NJ) Harbor. The distribution of toxicity quotients is obtained using a food chain model for the osprey and specifying distributions for input parameters, which are disaggregated to represent either uncertainty or variability. PCB concentrations in sediment and water are treated as predominantly uncertain, whereas lipid content in fish, feeding preferences, and fish weight are assumed to contribute primarily to population variability in PCB accumulation. The analysis shows that point estimates of reasonable maximum exposure (RME) exceed the uncertainty bounds on the 95th percentile of variability. The analysis also shows that uncertainties in the sediment and water contaminant concentrations contribute more to the range of risk estimates than does the variability in the population exposure parameters. The separation of uncertainty and variability in food chain models can help to support management decisions regarding dredged material disposal by providing a quantitative expression of the confidence in ecological risk estimates. A rationale is provided for the distinction between uncertain and variable parameters based on management goals and data availability.

Animals↗

Reconstruction of doses from radionuclide inhalation for nuclear power plant workers using air concentration measurements and associated uncertainties.

This paper presents a case study to illustrate the influence of parameter uncertainties on calculating an internal radiation dose of one actual nuclear plant worker, alias Mr. X, as well as the utility of air sampling for internal dose reconstruction. Input probability distributions for air concentrations of radionuclides were derived from empirical air measurements taken by fixed area air samplers. The total internal dose was calculated by multiplying radionuclide intake by dose conversion factors in Monte-Carlo simulations. There is significant variability in dose conversion factors and uncertainty in the estimated concentrations of radionuclides in the air to which Mr. X was exposed. The high variability and uncertainty of the model parameters contributed to large ranges of predicted internal doses for Mr. X. Two-dimensional Monte-Carlo simulations were conducted to separate contributions of the uncertainty and variability. Sensitivity analysis was conducted to determine which of the input parameters contributed most to uncertainty in internal dose estimates. Our analysis suggests that the uncertainty resulting from use of general air surveys contributes more to the internal dose ranges than the variability from DCFs and other population-derived parameters. Reduction of the uncertainty in reconstructed internal dose can be achieved by using personal air sampling and/or individual bioassays and regular whole-body counting.

Air Pollutants, Radioactive↗

Spatially explicit exposure models: application to military sites.

As a result of defense-related activities, large areas of valuable habitats can be physically disturbed and/or contaminated by hazardous pollutants. It is, however, important to understand that the military impact on such areas may not be wholly detrimental to the environment: their closure to the public can result in environmental conservation of large portions of habitat. Many former military ranges have been converted for civil usage; others are still actively operated for military purposes. In both cases, a major task for environmental policy- and decision-makers is to determine scientifically justified reuse and/or operation scenarios that would not result in deterioration of site habitats and that would in fact be favorable to further development of biodiversity within the areas' existing ecosystems. Ecological risk assessment is suggested as the key process to use in facilitating the assessment of the ecological value of contaminated and/or disturbed military sites and in the development of a reuse decision protocol. We are currently developing and integrating a number of risk and habitat assessment techniques into such a protocol. This paper presents our approach to one aspect of this system: the incorporation of spatial information into ecological risk assessment. We present a software prototype that calculates radionuclide accumulation by deer foraging in areas having specified contamination patterns.

Decision Support Techniques↗

Biological behavior of human breast cancer micrometastases.

PURPOSE: Clinically undetectable micrometastases may account for disease recurrence in breast cancer patients after variable disease-free intervals. However, little is known about the cellular mechanisms controlling human breast cancer micrometastases. We compared tumor proliferation rate, apoptotic index, and angiogenesis in human breast cancer micrometastases with those of macroscopic axillary lymph node metastases. EXPERIMENTAL DESIGN: Seven breast cancer micrometastases (<2 mm) obtained from the sentinel nodes of seven patients were compared with 13 macrometastases (lymph node replaced with tumor) obtained from 13 patients. The tissue was fixed in formalin, embedded in paraffin, serially sectioned, and evaluated by H&E and immunohistochemistry for cytokeratin. Tumor proliferation rate was assessed as the number of Ki-67-positive nuclei/total number of tumor nuclei. Tumor vascularity was quantified using antibody to factor VIII to identify microvessels per high-power field (at x400). Apoptosis was quantified using the terminal deoxynucleotidyl transferase (Tdt)-mediated nick end labeling method. Results were analyzed with the Wilcoxon rank-sum test. RESULTS: Median size of micrometastases was 0.5 mm (range, 0.4-1.0), and the median number of tumor nuclei/section was 143 (range, 90-312). Median proliferation rate for macrometastases was greater than for micrometastases (35% versus 12%; P = 0.003). Median microvessel density/high-power field for macrometastases was greater than for micrometastases (17 versus 1; P < 0.001). There was no difference in apoptotic index between macrometastases and micrometastases (1.1% versus 0.7%; P = not significant). CONCLUSIONS: Human breast cancer micrometastases have lower tumor proliferation rates and angiogenesis than breast cancer macrometastases. These characteristics may explain their differential growth patterns.

Adult↗

Correlations among tumor types in mouse cancer bioassays: liver adenomas, liver carcinomas, leukemias and lymphomas.

In an examination of rodent bioassays Young and Gries [Young S.S., and Gries C.L. Exploration of the negative correlation between proliferative hepatocellular lesions and lymphoma in rats and mice--establishment and implications. Fundam. Appl. Toxicol. 1984: 4: 632-6401 and Haseman et al. [Haseman J.K., et al. Body weight-tumor incidence correlations in long-term rodent carcinogenicity studies. Toxicol. Pathol. 1997: 25: 256-263] noticed that there is a negative correlation (anticorrelation) between development of liver tumors and leukemia or lymphomas. If an animal has a lymphoma or leukemia it is less likely to develop liver tumors. These studies noted that this applies to several strains of animals. The anticorrelation appeared in control animals. In this paper we study this anticorrelation in the quarter of a million rodents exposed in the Carcinogenesis Bioassay Database System (CBDS) database of the National Toxicology program in both control and dosed animals. We failed to completely replicate Young and Gries or Haseman et al. However, when benign liver tumors (adenomas or nodules) and malignant liver tumors (carcinomas) are considered separately AND different leukemia and lymphoma types are considered, a strong anticorrelation appears. We identify survival and the time period (in years) during which the bioassay was completed as an important factor in interpreting correlations and anticorrelations. Differences between liver adenomas and carcinomas and lymphoma types contribute to a more general question of grouping of the individual tumor types. In our classification scheme (originally developed about 1986 by Dr. Bailar) an effort is made to distinguish benign and malignant neoplasms, while other investigators group all tumors at a specific site. For many analyses liver adenomas and carcinomas have been lumped together. This is because it is suspected that the diagnoses by pathologists may not distinguish, or ignore the (benign) adenoma when a (malignant) carcinoma is present. Possible biological differences in tumor mechanisms may require separate evaluation of these tumors with all the dangers of "pathologist bias" that this introduces.

Adenoma↗

Weight and survival depression in rodent bioassays with and without tumor decreases.

It has been suggested that the decreased tumor rates (anticarcinogenicity) commonly observed in the National Toxicology Program (NTP) rodent bioassays may be caused by compound-induced decreases in body weight or decreases in survival of treated animals. In this study, weight decrement and survival depression following chemical treatment was studied for those chemicals which induce site specific decreases in tumor rates (anticarcinogens) and those which do not (non-anticarcinogens) in a database of 312 chemicals tested in the NTP bioassay program prior to 1983. There is an evident difference in weight depression and animal survival between anticarcinogens and non-anticarcinogens but it is small relative to the variability between chemicals in the two groups. We argue that weight or survival depression cannot, in a simple way, explain the difference between anticarcinogenic and non-anticarcinogenic chemicals. In fact, there are a number of chemicals that are anticarcinogenic with no evidence of weight or survival depression and many chemicals that cause significant weight or survival decreases with no apparent anticarcinogenic effects. There is a small but statistically insignificant relationship between the degree of weight depression and the number of tumor sites found to have lower tumor rates in treated animals. These analyses suggest that biological factors other than weight and survival depression are involved in decreased tumor rates in rodent bioassays. These results, and those of the companion paper (I. Linkov et al., this issue), suggest that the anticarcinogenic responses observed in rodent cancer bioassays should be carefully considered in evaluations of the overall carcinogenic potential of chemicals.

Animals↗

Anticarcinogenic responses in rodent cancer bioassays are not explained by random effects.

Anticarcinogenicity in a long-term rodent bioassay is defined as a statistically significant decrease of a specific tumor type in a dosed group following chemical exposure. About 92% of chemicals tested by the National Toxicology Program prior to 1983 reveal at least one site with a significant (p < or = 0.05) tumor rate decrease in one or more tested groups, a result consistent with those of J. K. Haseman and F. M. Johnson (1996, Mutat. Res. 350, 131-141) for a database of recently tested chemicals. Detection of tumor decreases in a specific site can be explained not only by biological effects, but also as a result of random variability in the background tumor rates, decreases in body weight, or decreases in survival of treated animals. This paper evaluates the rate of false-positive anticarcinogenic findings due to random effects (variations in tumor rates and the multiple comparisons undertaken in evaluating a bioassay), while a companion paper addresses the influence of weight and survival depression. Monte-Carlo simulation was conducted to assess the contribution of random effects. This contribution was found to be important even when a statistical significance cutoff of p0 < or = 0.05 was chosen. If a more stringent statistical criterion was used (p0 < or = 0.01 or p < or = 0.005), the proportion of false positive determinations diminishes. The number of anticarcinogens in the database remains substantially higher than predicted by the stimulations. An examination of the distribution of all p values (T. Schweder and E. Spjøtvoll, 1982, Biometrika 69, 493-502) also indicates that statistically significant anticarcinogenic responses are found in the database at a higher rate than would result from purely random responses. Finally, the cross-species prediction of anticarcinogenic responses was examined in a manner similar to a study of cross-species prediction of carcinogenic responses (G. M. Gray et al., 1995, Reg. Toxicol. Pharmacol. 20, 281-301). The analyses show that anticarcinogenic effects in one rodent species predict well anticarcinogenic effect in another rodent species. It seems likely that biological factors are involved in anticarcinogenic responses observed in rodent cancer bioassays.

Animals↗

Polymorphous low-grade adenocarcinoma of minor salivary glands: a study of 17 cases with emphasis on cell differentiation.

AIMS: The diagnosis of polymorphous low-grade adenocarcinoma (PLGA) of salivary glands remains difficult for general surgical pathologists. In an effort to understand the morphological heterogeneity of these neoplasms and facilitate their recognition we reviewed the architectural patterns, cell differentiation and immunohistochemical features of 17 case of PLGA. METHODS AND RESULTS: There were 11 females and six males with a mean age of 58 years. Twelve tumours were located in the palate, two in the posterior third of the tongue, and one each in the upper lip, buccal mucosa and retromolar triangle. Two patients presented with neck metastases. The mean tumour size was 20 mm (range 6-50 mm). The tumour cells were arranged in five architectural patterns: tubules and small duct-like structures; cords and trabeculae; solid nests; cribriform areas and papillae. Twelve (71%) cases were composed of a combination of tubules and small duct-like structures, cords and trabeculae, and solid nests. Cribriform areas with pseudoluminal spaces were seen in six (35%) cases. A focal papillary pattern was evident in three cases and constituted 40% of the tumour in one. Perineural invasion was seen in 13 cases (76%). All cases studied were positive for CAM5.2, 34BE12, vimentin and S100 protein and showed overexpression of bcl-2 protein. Rb protein was present in 13 cases whereas p53 expression was absent in all cases. The average proliferation index (PI) was 7% (range 1-17%). Three patients developed local recurrences with cervical lymph node metastases but no patient died as result of tumour. No morphological features were found to be prognostic for the development of local recurrences or lymph nodes metastases. CONCLUSIONS: PLGA is a distinctive neoplasm of salivary glands formed by luminal and nonluminal tumour cells with limited patterns of architectural differentiation. The relative proportion of these cells seems to play a significant role in the morphogenesis of these tumours. The overexpression of the bcl-2 protein and the low PI suggest that inhibition of programmed cell death may be involved in the oncogenesis of PLGA.

Adenocarcinoma↗

Remedial policies in radiologically-contaminated forests: environmental consequences and risk assessment.

As a result of the Chernobyl nuclear power plant accident in 1986, large forested areas in Europe were contaminated by radionuclides. Extensive societal pressure has been exerted to decrease the radiation dose to the population and to the environment. Thus, in making abatement and remediation policy decisions not only economic costs, but also human and environmental risk assessment are desired. Forest remediation by organic layer removal, one of the most promising cleanup policies, is considered in this paper. Ecological risk assessment requires evaluation of the radionuclide distribution in forests. The FORESTPATH model is used for predicting the radionuclide fate in forest compartments after deposition as well as for evaluating the application of the remedial policy. Time of intervention and radionuclide deposition profile was predicted as being crucial for the remediation efficiency. Risk assessment conducted for a critical group of forest users in Belarus shows that consumption of forest products (berries and mushrooms) leads to about 0.004% risk of a fatal cancer. Cost-benefit analysis for forest cleanup suggests that complete removal of organic layer is too expensive for application in Belarus.

Cost-Benefit Analysis↗

Cyclin D1 and retinoblastoma protein expression in Kaposi's sarcoma.

Cyclins are implicated in the induction and control of the cell cycle. Cyclin D1 regulates G1-phase progression by phosphorylation of the retinoblastoma protein (pRb). The Kaposi's sarcoma-associated herpesvirus/human herpesvirus 8 (KSHV) contains and transcribes an open reading frame with sequence similarities to cellular D-type cyclins. The KSHV-cyclin protein is associated with kinase activity capable of phosphorylating pRb in vitro. Here, we study for the first time the endogenous cyclin D1 and Rb protein expression in Kaposi's sarcoma (KS) tissue. Twenty-four consecutive biopsies of AIDS-related (n=21) and classical (n=3) KS were studied by immunohistochemistry with monoclonal antibodies against cyclin D1 and pRb. We detected cyclin D1 in 1 of 13 patch/plaque stage, in 4 of 5 nodular stage and in 3 of 6 visceral KS lesions. By Western blot analysis, this cellular cyclin D1 monoclonal antibody did not cross-react with the purified KSHV-cyclin protein. The pRb was consistently detected in 24 of 24 KS lesions. In summary, early KS lesions rarely have detectable expression of endogenous cyclin D1. Advanced and disseminated KS lesions tend to have overexpression of endogenous cyclin D1. Therefore, cellular cyclin D1 expression appears to correlate with tumor progression in KS. The endogenous cyclin D1 is antigenically distinct from the KSHV-cyclin homolog. The pRb, which may serve as a substrate for KSHV-cyclin, is found in all KS lesions examined.

Antibodies, Monoclonal↗

Glutathione S-transferase PI (GST-pi) class expression by immunohistochemistry in benign and malignant prostate tissue.

PURPOSE: Glutathione S-transferase (GST) enzymes may prevent carcinogenesis through inactivation of reactive electrophiles by conjugation to reduced glutathione. Recently, it was reported that most prostate cancers fail to express GST-pi despite an abundant presence in benign prostate tissue, suggesting a common genetic alteration. To define its presence in prostate tissue, we evaluated GST-pi expression in a variety of prostate tissues. MATERIALS AND METHODS: Immunostaining with anti-GST-pi antibody was performed on 69 benign prostates, 44 malignant prostates, 12 incidental prostate carcinomas and 17 prostatic intraepithelial neoplasia (PIN) specimens. Specimens were evaluated for the presence and percent of GST-pi. Within benign tissue, GST-pi immunostaining was distinguished between basal cells and secretory acinar epithelium. RESULTS: In benign epithelium, the basal cells demonstrated intense staining in all cases. The mean percent staining among the basal cells was 67% (R 40-90%). The acinar epithelium stained weakly positive in 94% (65/69) of specimens, however the mean percent staining was only 5% (R 0-25%). GST-pi was detected in only 3.5% (2/56) of the prostate cancers. No incidental prostate cancers and only one (6%) high grade PIN stained positive. CONCLUSIONS: Our study confirms the absence of GST-pi expression in prostate cancer and high grade PIN. Furthermore, GST-pi expression correlates well with the basal cell phenotype, but not with benign epithelial cells. The lack of staining among prostate cancer cells may reflect the absence of a basal cell layer, suggesting that GST-pi is involved more in epithelial differentiation and questioning its role in the malignant transformation of prostatic acinar cells.

Epithelium↗