Biodosimetry in interventional radiology: cutaneous-based immunoassay for anticipating risks of dermatitis

OBJECTIVES

Interventional radiology procedures expose individuals to ionizing radiation. However, existing dosimetry methods do not provide the dose effectively absorbed to the skin, and do not consider the patient's individual response to irradiation. To resolve this lack of dosimetry data, we developed a new external irradiation biodosimetry device, DosiKit, based on the dose-dependent relationship between irradiation dose and radiation-induced H2AX protein phosphorylation in hair follicles. This new biological method was tested in Clermont-Ferrand University Hospital to evaluate the assay performances in the medical field and to estimate DosiKit sensitivity threshold.

METHODS

DosiKit was tested over 95 patients treated with neuroradiological interventions. For each intervention, lithium fluoride thermoluminescent dosimeters (TLD) were used to measure total dose received at each hair collection point (lateral and occipital skull areas), and conventional indirect dosimetry parameters were collected with a Dosimetry Archiving and Communication System (DACS).

RESULTS

Quantitative measurement of radiation-induced H2AX protein phosphorylation was performed on 174 hair samples before and after the radiation exposure and 105 samples showed a notable induction of gammaH2AX protein after the radiological procedure. According to a statistical analysis, the threshold sensitivity of the DosiKit immunoassay was estimated around 700 mGy.

CONCLUSIONS

With this study, we showed that DosiKit provides a useful way for mapping the actually absorbed doses, allowing to identify patients overexposed in interventional radiology procedures, and thus for anticipating risk of developing dermatitis.

KEY POINTS

• DosiKit is a new external irradiation biodosimetry device, based on the dose-dependent relationship between irradiation dose and radiation-induced H2AX protein phosphorylation in hair follicles. • DosiKit was tested over 95 patients treated with neuroradiological interventions. • The threshold sensitivity of the DosiKit immunoassay was estimated around 700 mGy and DosiKit provides a useful way for mapping the actually absorbed doses.

Deployment of the DosiKit System Under Operational Conditions: Experience From a French Defense National Nuclear Exercise

Estimation of the dose received by accidentally irradiated victims is based on a tripod: clinical, biological, and physical dosimetry. The DosiKit system is an operational and mobile biodosimetry device allowing the measurement of external irradiation directly on the site of a radiological accident. This tool is based on capillary blood sample and hair follicle collection. The aim is to obtain a whole-body and local-surface dose assessment. This paper is about the technical evaluation of the DosiKit; the analytical process and scientific validation are briefly described. The Toulon exercise scenario was based on a major accident involving the reactor of a nuclear attack submarine. The design of the scenario made it impossible for several players (firefighters, medical team) to leave the area for a long time, and they were potentially exposed to high dose rates. The DosiKit system was fully integrated into a deployable radiological emergency laboratory, and the response to operational needs was very satisfactory.

Opposite effects of GCN5 and PCAF knockdowns on the alternative mechanism of telomere maintenance

Cancer cells can use a telomerase-independent mechanism, known as alternative lengthening of telomeres (ALT), to elongate their telomeres. General control non-derepressible 5 (GCN5) and P300/CBP-associated factor (PCAF) are two homologous acetyltransferases that are mutually exclusive subunits in SAGA-like complexes. Here, we reveal that down regulation of GCN5 and PCAF had differential effects on some phenotypic characteristics of ALT cells. Our results suggest that GCN5 is present at telomeres and opposes telomere recombination, in contrast to PCAF that may indirectly favour them in ALT cells.

Comparative analysis of micro-RNAs in human papillomavirus-positive versus -negative oropharyngeal cancers

BACKGROUND

Oncogenic mechanisms of human papillomavirus (HPV)-positive oropharyngeal cancer are still poorly characterized. Analysis of their microRNA expression profile might provide valuable information.

METHODS

The microRNA expression profiles were analyzed by micro-arrays in 26 oropharyngeal cancers. A microRNA signature specific to HPV-status was identified by analyzing a learning/training set consisting of 16 oropharyngeal cancers. The robustness of this signature was further confirmed by blind case-by-case classification of a validation set composed of 10 independent tumors. Putative targeted molecular pathways were proposed using DIANA miRPath online software (http://microrna.gr/mirpath).

RESULTS

We have identified 25 miRNA signatures, which discriminates HPV16-positive oropharyngeal cancer from their HPV-negative counterparts. These 25 microRNAs play a potential role in Wnt and PI3K-pathways, cell-adhesion/cell-polarity, and the cytoskeleton regulation.

CONCLUSION

Our study contributes to a better understanding of pathogenic mechanisms involved in the development of HPV-positive oropharyngeal cancer and in the identification of potential therapeutic molecular targets. © 2016 Wiley Periodicals, Inc. Head Neck 38: 1708-1716, 2016.

A predictive transcriptomic signature of oropharyngeal cancer according to HPV16 status exclusively

OBJECTIVE

Human-papillomaviruses (HPV) type 16 is a causative agent in an increasing subset of oropharyngeal squamous cell carcinomas (OPSCCs). These tumors have distinct oncogenic mechanisms and a more favorable prognosis than tobacco-induced OPSCCs. Although these differences emphasize the need for a specific therapeutic approach, HPV status is still not used to guide treatment. A better characterization of the molecular profile related to HPV16-induced OPSCC might help to develop personalized treatments.

PATIENTS AND METHODS

Using a human whole-genome DNA-microarray, we have examined the gene expression profiles in 15 HPV-negative and 15 transcriptionally-active HPV-positive OPSCCs. The study was conducted in two steps. Firstly, a learning/training-set consisting of 8 HPV16-positive and 8 HPV16-negative OPSCCs was analyzed to identify a specific signature. Potentially confounding factors (stage, sex and tobacco) were equally distributed in both groups. Subsequently the robustness of this signature was confirmed by blind case-by-case classification of a validation-set composed of the 14 remaining tumors.

RESULTS

We have identified a signature composed of 224 genes, which discriminates HPV16-induced OPSCC from their HPV-negative counterparts. After the blind classification of the 14 tumours, the viral status was revealed: 13 out of 14 tumors were correctly classified according to tumor etiology, 1/14 was not determined and none were misclassified. Several of the differentially expressed genes were involved in cell-cycle regulation, DNA replication and repair, transcription regulation, immune response and apoptosis.

CONCLUSION

Our study contributes to a better understanding of pathogenic mechanisms involved in the development of HPV-positive OPSCCs and in the identification of potential therapeutic targets.

Comparison of transcriptomic signature of post-Chernobyl and postradiotherapy thyroid tumors

BACKGROUND

We previously identified two highly discriminating and predictive radiation-induced transcriptomic signatures by comparing series of sporadic and postradiotherapy thyroid tumors (322-gene signature), and by reanalyzing a previously published data set of sporadic and post-Chernobyl thyroid tumors (106-gene signature). The aim of the present work was (i) to compare the two signatures in terms of gene expression deregulations and molecular features/pathways, and (ii) to test the capacity of the postradiotherapy signature in classifying the post-Chernobyl series of tumors and reciprocally of the post-Chernobyl signature in classifying the postradiotherapy-induced tumors.

METHODS

We now explored if postradiotherapy and post-Chernobyl papillary thyroid carcinomas (PTC) display common molecular features by comparing molecular pathways deregulated in the two tumor series, and tested the potential of gene subsets of the postradiotherapy signature to classify the post-Chernobyl series (14 sporadic and 12 post-Chernobyl PTC), and reciprocally of gene subsets of the post-Chernobyl signature to classify the postradiotherapy series (15 sporadic and 12 postradiotherapy PTC), by using conventional principal component analysis.

RESULTS

We found that the five genes common to the two signatures classified the learning/training tumors (used to search these signatures) of both the postradiotherapy (seven PTC) and the post-Chernobyl (six PTC) thyroid tumor series as compared with the sporadic tumors (seven sporadic PTC in each series). Importantly, these five genes were also effective for classifying independent series of postradiotherapy (five PTC) and post-Chernobyl (six PTC) tumors compared to independent series of sporadic tumors (eight PTC and six PTC respectively; testing tumors). Moreover, part of each postradiotherapy (32 genes) and post-Chernobyl signature (16 genes) cross-classified the respective series of thyroid tumors. Finally, several molecular pathways deregulated in post-Chernobyl tumors matched those found to be deregulated in postradiotherapy tumors.

CONCLUSIONS

Overall, our data suggest that thyroid tumors that developed following either external exposure or internal (131)I contamination shared common molecular features, related to DNA repair, oxidative and endoplasmic reticulum stresses, allowing their classification as radiation-induced tumors in comparison with sporadic counterparts, independently of doses and dose rates, which suggests there may be a "general" radiation-induced signature of thyroid tumors.

Use of gene expression signature to discriminate oropharyngeal cancers according to HPV16 status

6055

Background: Strong evidence supports the hypothesis that high-risk human papillomavirus (HPV), particularly HPV16, is a causative agent for an increasing subset of oropharyngeal squamous cell carcinomas (OPSCC). These tumors have distinct oncogenic mechanisms and a more favorable prognosis than tobacco induced OPSCC. Although these differences emphasize the need for a specific therapeutic approach, HPV status is still not used to guide treatment. A better understanding of the molecular profile related to HPV16 induced OPSCC may help to develop personalized treatments. Methods: To identify an HPV16-related molecular signature, we compared the gene expression profile of 15 transcriptionally active HPV16-positive and 15 HPV16-negative OPSCC. The study was conducted in two steps. First, a learning set of 16 OPSCC comprising 8 HPV16-positives and 8 HPV16-negatives OPSCC was analyzed in order to identify the signature. Potentially confounding factors of stage, sex and tobacco consumption were equally distributed in both groups. Secondarily, the robustness of this signature was further confirmed by blind case-by-case classification of an independent set of 14 OPSCC. Results: We identified a signature composed of 224 genes which discriminates HPV16-induced OPSCC from their tobacco induced counterparts. After the viral status was revealed, 13 out of 14 tumors were correctly classified according to tumor etiology, 1/14 was undetermined and none were misclassified. Interestingly, deregulated genes in HPV16-positive tumors are principally involved in innate immunity, in cell cycle regulation through the TP53/RB/E2F pathway, and autophagy through mTOR regulation. Well known targets of E6 and E7 proteins are also found to be deregulated. Conclusions: Our results demonstrate that a set of selected genes can distinguish OPSCC according to etiology. These genes shed light on HPV16 induced carcinogenesis since specific molecular pathways are deregulated. Further investigations are required for a better understanding of the differing natural histories and biological properties of these tumors. These properties may be exploited as a target of novel therapeutic agents in HPV-related OPSCC.

Discriminating gene expression signature of radiation-induced thyroid tumors after either external exposure or internal contamination

Both external radiation exposure and internal radionuclide contamination are well known risk factors in the development of thyroid epithelial tumors. The identification of specific molecular markers deregulated in radiation-induced thyroid tumors is important for the etiological diagnosis since neither histological features nor genetic alterations can discriminate between sporadic and radiation-induced tumors. Identification of highly discriminating markers in radiation-induced tumors is challenging as it relies on the ability to identify marker deregulation which is associated with a cellular stress that occurred many years before in the thyroid cells. The existence of such a signature is still controversial, as it was not found in several studies while a highly discriminating signature was found in both post-radiotherapy and post-Chernobyl series in other studies. Overall, published studies searching for radiation-induced thyroid tumor specificities, using transcriptomic, proteomic and comparative genomic hybridization approaches, and bearing in mind the analytical constraints required to analyze such small series of tumors, suggest that such a molecular signature could be found. In comparison with sporadic tumors, we highlight molecular similarities and specificities in tumors occurring after high-dose external radiation exposure, such as radiotherapy, and in post-Chernobyl tumors that occurred after internal 131I contamination. We discuss the relevance of signature extrapolation from series of tumors developing after high and low doses in the identification of tumors induced at very low doses of radiation.

Aging and photo-aging DNA repair phenotype of skin cells-evidence toward an effect of chronic sun-exposure

Several studies have demonstrated the deleterious effect of aging on the capacity of cells to repair their DNA. However, current existing assays aimed at measuring DNA repair address only a specific repair step dedicated to the correction of a specific DNA lesion type. Consequently they provide no information regarding the repair pathways that handle other types of lesions. In addition to aging, consequences of photo-exposure on these repair processes remain elusive. In this study we evaluated the consequence of aging and of chronic and/or acute photo-exposure on DNA repair in human skin fibroblasts using a multiplexed approach, which provided detailed information on several repair pathways at the same time. The resulting data were analyzed with adapted statistics/bioinformatics tools. We showed that, irrespective of the repair pathway considered, excision/synthesis was less efficient in non-exposed cells from elderly compared to cells from young adults and that photo-exposure disrupted this very clear pattern. Moreover, it was evidenced that chronic sun-exposure induced changes in DNA repair properties. Finally, the identification of a specific signature at the level of the NER pathway in cells repeatedly exposed to sun revealed a cumulative effect of UVB exposure and chronic sun irradiation. The uses of bioinformatics tools in this study was essential to fully take advantage of the large sum of data obtained with our multiplexed DNA repair assay and unravel the effects of environmental exposure on DNA repair pathways.

A transcriptome signature distinguished sporadic from postradiotherapy radiation-induced sarcomas

Exposure to ionizing radiation is a known risk factor for cancer. However, up to now, rigorously defined scientific criteria that could establish case-by-case the radiation-induced (RI) origin of a tumour have been lacking. To identify genes that could constitute a RI signature, we compared the transcriptome of 12 sarcomas arising in the irradiation field of a primary tumour following radiotherapy with the transcriptome of 12 sporadic sarcomas. This learning/training set contained four leiomyosarcomas, four osteosarcomas and four angiosarcomas in each subgroup. We identified a signature of 135 genes discriminating RI from sporadic sarcomas. The robustness of this signature was tested by the blind case-by-case classification of an independent set of 36 sarcomas of various histologies. Thirty-one sarcomas were classified as RI or sporadic; it was not possible to propose an aetiology for the five others. After the code break, it was found that one sporadic sarcoma was misclassified as RI. Thus, the signature is robust with a sensitivity of 96%, a positive and a negative predictive value of 96 and 100%, respectively and a specificity of 62%. The functions of the genes of the signature suggest that RI sarcomas were subject to chronic oxidative stress probably due to mitochondrial dysfunction.

Gene expression signature discriminates sporadic from post-radiotherapy-induced thyroid tumors

Both external and internal exposure to ionizing radiation are strong risk factors for the development of thyroid tumors. Until now, the diagnosis of radiation-induced thyroid tumors has been deduced from a network of arguments taken together with the individual history of radiation exposure. Neither the histological features nor the genetic alterations observed in these tumors have been shown to be specific fingerprints of an exposure to radiation. The aim of our work is to define ionizing radiation-related molecular specificities in a series of secondary thyroid tumors developed in the radiation field of patients treated by radiotherapy. To identify molecular markers that could represent a radiation-induction signature, we compared 25K microarray transcriptome profiles of a learning set of 28 thyroid tumors, which comprised 14 follicular thyroid adenomas (FTA) and 14 papillary thyroid carcinomas (PTC), either sporadic or consecutive to external radiotherapy in childhood. We identified a signature composed of 322 genes which discriminates radiation-induced tumors (FTA and PTC) from their sporadic counterparts. The robustness of this signature was further confirmed by blind case-by-case classification of an independent set of 29 tumors (16 FTA and 13 PTC). After the histology code break by the clinicians, 26/29 tumors were well classified regarding tumor etiology, 1 was undetermined, and 2 were misclassified. Our results help shed light on radiation-induced thyroid carcinogenesis, since specific molecular pathways are deregulated in radiation-induced tumors.

Abstract 5636: Gene expression signature discriminates sporadic from post-radiotherapy radiation-induced sarcomas

The purpose of the study is to identify markers that could define a robust signature discriminating case by case radiation-induced tumors from their sporadic counterparts. The rare occurrence of human radiation-induced tumors increases the difficulty of their identification. Nevertheless, in case of sarcomas occurring in the irradiation field after radiotherapy for a primary neoplasm, stringent criteria allow the radiation-induced etiology to be established with a high level of confidence. However, the available series remains limited. Global transcriptome studies are particularly affected by this problem since the methods used for data analysis are generally efficient only for long series. In order to solve this problem, we have developped new methods of classification, based on transcriptome analysis, for the case by case tumor diagnosis. To find a signature we first select a set of candidate genes, using Expectation-Maximisation algorithm, on a learning set of tumors. Second, using a training set of tumors, we select the genes with the higher potential for classifying the tumors. Then, the robustness of the signature was tested by blindly classifying an independent set of tumors.

Using a learning/training set of 12 radiation-induced (RI) and 12 sporadic (SP) sarcomas including angiosarcomas, leiomyosarcomas and osteosarcomas, we identified a minimal signature of 143 genes discriminating the sarcomas according to the etiology. A larger signature of 1100 genes, using less stringent criteria of classification was also established. The robustness of these signatures was tested by the blindly case by case classification of an independent set of 22 RI and 14 SP sarcomas of various histologies. After the histology code-break, 28/36 sarcomas were well-classified using the minimal signature, in 6 cases (1 RI and 5 SP) the etiology could not be established whereas 2 SP sarcomas were classified as RI. Using the large signature, the etiology was not determined in 4 cases (1 RI and 3 SP) and the 32 other sarcomas were well-classified. Several pathway were found differentially expressed according to the etiology. Notably, the NRF2-mediated oxidative stress response pathway, the ubiquitination-deubiquitination pathways and several genes coding subunits of the 26S proteasome and heat shock proteins underwent a general up regulation in RI sarcomas. These data suggest that RI sarcomas are submitted to oxidative stress that could generate the formation of mis-folded and oxidated proteins further degradated by the ubiquitination-deubiquitination-proteasome pathway. In this study, we identify a robust signature discriminating radiation-induced from sporadic sarcomas, opening the possibility to recognise, case by case, the implication of ionizing radiation in a tumor formation.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5636.

Are adenosquamous lung carcinomas a simple mix of adenocarcinomas and squamous cell carcinomas, or more complex at the molecular level?

Adenocarcinomas (AC), squamous cell carcinomas (SCC) and adenosquamous carcinomas (ASC) are three histological subtypes of non-small-cell lung carcinomas (NSCLC). ASC are morphologically mixed tumours that contain the two cell components AC and SCC. To understand if they are a "simple" mix of AC and SCC or if they present molecular specificities, as compared with the molecular characterization of both components, we performed a comparative transcriptome analysis on a series of nine ASC, five AC and five SCC induced in rats by radon exposure. We found that 72, 40 and 39 genes were differentially expressed when comparing AC_SCC, ASC_SCC and AC_ASC, respectively. Moreover, when classifying the three histological subtypes, using genes that discriminated AC and SCC, we observed that all ASC were classified as intermediate between the AC and SCC, some being closer to AC, others to SCC. These results indicated that, regarding gene expression, ASC could be considered as a mix of AC and SCC, both in various proportions. However, they also exhibit molecular specificities since we found specific genes discriminating ASC_SCC and AC_ASC. In conclusion, the ASC mixed lung tumours are more complex than simple mixes of AC and SCC components. Neuroendocrine differentiation and ERK proliferation pathways seemed preferentially deregulated in ASC compared to AC and SCC respectively, pathways that are worthy of being explored because they could partially explain the high clinical aggressiveness of ASC.

Silencing of Cited2 and Akap12 genes in radiation-induced rat osteosarcomas

We have previously studied genomic copy number changes and global gene expression patterns in rat osteosarcomas (OS) induced by the bone-seeking alpha emitter (238)Pu by comparative genomic hybridization (CGH) and oligonucleotide microarray analyses, respectively. Among the previously identified genes that were down-regulated in radiation-induced rat OS tumors, Cited2 (Cbp/p300-interacting transactivator, with Glu/Asp-rich carboxy-terminal domain, 2) and Akap12 (a kinase anchoring protein, also known as src-suppressed C-kinase substrate, SSeCKS) genes mapped to the most frequently lost regions on chromosome 1p. In the present study, relative copy number losses of Cited2 and Akap12 genes were observed in 8 of 15 (53%) and 10 of 15 (67%) tumors by quantitative PCR analysis. Loss of Cited2 and Akap12 in the tumors was confirmed at the levels of mRNA and protein expression by quantitative RT-PCR and immunoblot analyses, respectively. These results indicate that Cited2 and Akap12 are silenced in radiation-induced OS, and therefore are novel candidate tumor-suppressor genes of this tumor.

A microarray to measure repair of damaged plasmids by cell lysates

DNA repair mechanisms constitute major defences against agents that cause cancer, degenerative disease and aging. Different repair systems cooperate to maintain the integrity of genetic information. Investigations of DNA repair involvement in human pathology require an efficient tool that takes into account the variety and complexity of repair systems. We have developed a highly sensitive damaged plasmid microarray to quantify cell lysate excision/synthesis (ES) capacities using small amounts of proteins. This microsystem is based on efficient immobilization and conservation on hydrogel coated glass slides of plasmid DNA damaged with a panel of genotoxic agents. Fluorescent signals are generated from incorporation of labelled dNTPs by DNA excision-repair synthesis mechanisms at plasmid sites. Highly precise DNA repair phenotypes i.e. simultaneous quantitative measures of ES capacities toward seven lesions repaired by distinct repair pathways, are obtained. Applied to the characterization of xeroderma pigmentosum (XP) cells at basal level and in response to a low dose of UVB irradiation, the assay showed the multifunctional role of different XP proteins in cell protection against all types of damage. On the other hand, measurement of the ES of peripheral blood mononuclear cells from six donors revealed significant diversity between individuals. Our results illustrate the power of such a parallelized approach with high potential for several applications including the discovery of new cancer biomarkers and the screening of chemical agents modulating DNA repair systems.

Transcriptional response of wild-type and ataxia telangiectasia lymphoblasts following exposure to equitoxic doses of ionizing radiation

Experiments were designed to compare the transcriptional response to ionizing radiation (IR) of wild-type (WT) and ataxia telangiectasia (AT) cells. mRNA levels were assessed 2, 4 and 24 h after exposure to equitoxic doses using cDNA microarrays. Data reveal distinct patterns of gene expression between AT and WT cells since IR-responsive genes were mostly cell-type specific, this group representing 87 and 94% of the responding genes in WT and AT cells, respectively. In both cell lines, transcriptional alterations of genes associated with proliferation correlated with the observed cell cycle and growth data. Deregulated genes involved in apoptosis suggest that wild-type cells were more prone to cell death by apoptosis than AT cells. Furthermore, genes associated with the response to oxidative stress were particularly deregulated in wild-type cells whereas alterations of genes related to unexpected pathways including RNA processing, protein synthesis and lipid metabolism were specifically found in irradiated AT cells. These data suggest that under radiation conditions leading to a similar survival of WT and AT cells, the mechanisms triggered after radiation were mainly dependent on ATM status and thus on the intrinsic radiosensitivity.

Gene expression profiling of differentiated thyroid neoplasms: diagnostic and clinical implications

PURPOSE

The purpose of this research was to identify novel genes that can be targeted as diagnostic and clinical markers of differentiated thyroid tumors.

EXPERIMENTAL DESIGN

Gene expression analysis using microarray platform was performed on 6 pathologically normal thyroid samples and 12 primary follicular and papillary thyroid neoplasms. Microarrays containing probes for 5,760 human full-length cDNAs were used for hybridization with total RNA from normal and tumor thyroid samples labeled with Cy3-dUTP and Cy5-dUTP, respectively. Scanned array images were recorded, and data analysis was performed. Selected sets of differentially expressed genes were analyzed using quantitative real-time reverse transcription-PCR for verification.

RESULTS

We identified 155 genes that differentiate histologically normal thyroid tissues from benign and malignant thyroid neoplasms. Of these 75 genes were differentiated between follicular neoplasms (adenoma and carcinoma) and the follicular variant of papillary carcinoma. Purely follicular neoplasms (adenomas and carcinomas) shared many genetic profiles, and only 43 genes were distinctly different between these tumors. Hierarchical cluster analysis also differentiated conventional papillary carcinoma from its follicular variant and follicular tumors. The differentially expressed genes were composed of members of cell differentiation, adhesion, immune response, and proliferation associated pathways. Quantitative real-time reverse transcription-PCR analysis of selected genes corroborated the microarray expression results.

CONCLUSIONS

Our study show the following: (1) differences in gene expression between tumor and nontumor bearing normal thyroid tissue can be identified, (2) a set of genes differentiate follicular neoplasm from follicular variant of papillary carcinoma, (3) follicular adenoma and carcinoma share many of the differentiated genes, and (4) gene expression differences identify conventional papillary carcinoma from the follicular variant.