Photon iso-effective dose for cancer treatment with mixed field radiation based on dose-response assessment from human and an animal model: clinical application to boron neutron capture therapy for head and neck cancer.

Boron neutron capture therapy (BNCT) is a treatment modality that combines different radiation qualities. Since the severity of biological damage following irradiation depends on the radiation type, a quantity different from absorbed dose is required to explain the effects observed in the clinical BNCT in terms of outcome compared with conventional photon radiation therapy. A new approach for calculating photon iso-effective doses in BNCT was introduced previously. The present work extends this model to include information from dose-response assessments in animal models and humans. Parameters of the model were determined for tumour and precancerous tissue using dose-response curves obtained from BNCT and photon studies performed in the hamster cheek pouch in vivo models of oral cancer and/or pre-cancer, and from head and neck cancer radiotherapy data with photons. To this end, suitable expressions of the dose-limiting Normal Tissue Complication and Tumour Control Probabilities for the reference radiation and for the mixed field BNCT radiation were developed. Pearson's correlation coefficients and p-values showed that TCP and NTCP models agreed with experimental data (with r > 0.87 and p-values >0.57). The photon iso-effective dose model was applied retrospectively to evaluate the dosimetry in tumours and mucosa for head and neck cancer patients treated with BNCT in Finland. Photon iso-effective doses in tumour were lower than those obtained with the standard RBE-weighted model (between 10% to 45%). The results also suggested that the probabilities of tumour control derived from photon iso-effective doses are more adequate to explain the clinical responses than those obtained with the RBE-weighted values. The dosimetry in the mucosa revealed that the photon iso-effective doses were about 30% to 50% higher than the corresponding RBE-weighted values. While the RBE-weighted doses are unable to predict mucosa toxicity, predictions based on the proposed model are compatible with the observed clinical outcome. The extension of the photon iso-effective dose model has allowed, for the first time, the determination of the photon iso-effective dose for unacceptable complications in the dose-limiting normal tissue. Finally, the formalism developed in this work to compute photon-equivalent doses can be applied to other therapies that combine mixed radiation fields, such as hadron therapy.

Toward a clinical application of ex situ boron neutron capture therapy for lung tumors at the RA-3 reactor in Argentina.

PURPOSE: Many types of lung tumors have a very poor prognosis due to their spread in the whole organ volume. The fact that boron neutron capture therapy (BNCT) would allow for selective targeting of all the nodules regardless of their position, prompted a preclinical feasibility study of ex situ BNCT at the thermal neutron facility of RA-3 reactor in the province of Buenos Aires, Argentina. (l)-4p-dihydroxy-borylphenylalanine fructose complex (BPA-F) biodistribution studies in an adult sheep model and computational dosimetry for a human explanted lung were performed to evaluate the feasibility and the therapeutic potential of ex situ BNCT. METHODS: Two kinds of boron biodistribution studies were carried out in the healthy sheep: a set of pharmacokinetic studies without lung excision, and a set that consisted of evaluation of boron concentration in the explanted and perfused lung. In order to assess the feasibility of the clinical application of ex situ BNCT at RA-3, a case of multiple lung metastases was analyzed. A detailed computational representation of the geometry of the lung was built based on a real collapsed human lung. Dosimetric calculations and dose limiting considerations were based on the experimental results from the adult sheep, and on the most suitable information published in the literature. In addition, a workable treatment plan was considered to assess the clinical application in a realistic scenario. RESULTS: Concentration-time profiles for the normal sheep showed that the boron kinetics in blood, lung, and skin would adequately represent the boron behavior and absolute uptake expected in human tissues. Results strongly suggest that the distribution of the boron compound is spatially homogeneous in the lung. A constant lung-to-blood ratio of 1.3 ± 0.1 was observed from 80 min after the end of BPA-F infusion. The fact that this ratio remains constant during time would allow the blood boron concentration to be used as a surrogate and indirect quantification of the estimated value in the explanted healthy lung. The proposed preclinical animal model allowed for the study of the explanted lung. As expected, the boron concentration values fell as a result of the application of the preservation protocol required to preserve the lung function. The distribution of the boron concentration retention factor was obtained for healthy lung, with a mean value of 0.46 ± 0.14 consistent with that reported for metastatic colon carcinoma model in rat perfused lung. Considering the human lung model and suitable tumor control probability for lung cancer, a promising average fraction of controlled lesions higher than 85% was obtained even for a low tumor-to-normal boron concentration ratio of 2. CONCLUSIONS: This work reports for the first time data supporting the validity of the ovine model as an adequate human surrogate in terms of boron kinetics and uptake in clinically relevant tissues. Collectively, the results and analysis presented would strongly suggest that ex situ whole lung BNCT irradiation is a feasible and highly promising technique that could greatly contribute to the treatment of metastatic lung disease in those patients without extrapulmonary spread, increasing not only the expected overall survival but also the resulting quality of life.

Histamine reduces boron neutron capture therapy-induced mucositis in an oral precancer model.

OBJECTIVES: Searching for more effective and selective therapies for head and neck cancer, we demonstrated the therapeutic effect of boron neutron capture therapy (BNCT) to treat oral cancer and inhibit long-term tumor development from field-cancerized tissue in the hamster cheek pouch model. However, BNCT-induced mucositis in field-cancerized tissue was dose limiting. In a clinical scenario, oral mucositis affects patients' treatment and quality of life. Our aim was to evaluate different radioprotectors, seeking to reduce the incidence of BNCT-induced severe mucositis in field-cancerized tissue. MATERIALS AND METHODS: Cancerized pouches treated with BNCT mediated by boronophenylalanine at 5 Gy were treated as follows: control: saline solution; Hishigh : histamine 5 mg kg(-1) ; Hislow : histamine 1 mg kg(-1) ; and JNJ7777120: 10 mg kg(-1). RESULTS: Hislow reduced the incidence of severe mucositis in field-cancerized tissue to 17% vs CONTROL: 55%; Hishigh : 67%; JNJ7777120: 57%. Hislow was non-toxic and did not compromise the long-term therapeutic effect of BNCT or alter gross boron concentration. CONCLUSION: Histamine reduces BNCT-induced mucositis in experimental oral precancer without jeopardizing therapeutic efficacy. The fact that both histamine and boronophenylalanine are approved for use in humans bridges the gap between experimental work and potential clinical application to reduce BNCT-induced radiotoxicity in patients with head and neck cancer.

Design, construction and application of a neutron shield for the treatment of diffuse lung metastases in rats using BNCT.

A model of multiple lung metastases in BDIX rats is under study at CNEA (Argentina) to evaluate the feasibility of BNCT for multiple, non-surgically resectable lung metastases. A practical shielding device that comfortably houses a rat, allowing delivery of a therapeutic, uniform dose in lungs while protecting the body from the neutron beam is presented. Based on the final design obtained by numerical simulations, the shield was constructed, experimentally characterized and recently used in the first in vivo experiment at RA-3.

Biodistribution of the boron carriers boronophenylalanine (BPA) and/or decahydrodecaborate (GB-10) for Boron Neutron Capture Therapy (BNCT) in an experimental model of lung metastases.

BNCT was proposed for the treatment of diffuse, non-resectable tumors in the lung. We performed boron biodistribution studies with 5 administration protocols employing the boron carriers BPA and/or GB-10 in an experimental model of disseminated lung metastases in rats. All 5 protocols were non-toxic and showed preferential tumor boron uptake versus lung. Absolute tumor boron concentration values were therapeutically useful (25-76ppm) for 3 protocols. Dosimetric calculations indicate that BNCT at RA-3 would be potentially therapeutic without exceeding radiotolerance in the lung.

Boron neutron capture therapy for oral precancer: proof of principle in an experimental animal model.

OBJECTIVES: Field-cancerized tissue can give rise to second primary tumours, causing therapeutic failure. Boron neutron capture therapy (BNCT) is based on biological targeting and would serve to treat undetectable foci of malignant transformation. The aim of this study was to optimize BNCT for the integral treatment for oral cancer, with particular emphasis on the inhibitory effect on tumour development originating in precancerous conditions, and radiotoxicity of different BNCT protocols in a hamster cheek pouch oral precancer model. MATERIALS AND METHODS: Groups of cancerized hamsters were locally exposed to single or double (2 or 4 weeks apart) applications of BNCT at different dose levels, mediated by the boron compounds boronophenylalanine (BPA) or BPA and decahydrodecaborate (GB-10) administered jointly. Cancerized, sham-irradiated hamsters served as controls. Clinical status, tumour development from field-cancerized tissue and mucositis were followed for 8 months. RESULTS: A double application (4 weeks apart) of BNCT mediated by GB-10+ BPA at a total dose of 10 Gy in two 5-Gy doses rendered the best therapeutic advantage (63-100% inhibition of tumour development from field-cancerized tissue), minimizing dose-limiting mucositis. CONCLUSION: BNCT can be optimized for the integral treatment for head and neck cancer, considering the implications for field-cancerized tissue.

Boron neutron capture therapy (BNCT) inhibits tumor development from precancerous tissue: an experimental study that supports a potential new application of BNCT.

We previously demonstrated the efficacy of boron neutron capture therapy (BNCT) mediated by boronophenylalanine (BPA), GB-10 (Na(2)(10)B(10)H(10)) and (GB-10+BPA) to control tumors, with no normal tissue radiotoxicity, in the hamster cheek pouch oral cancer model. Herein we developed a novel experimental model of field-cancerization and precancerous lesions (globally termed herein precancerous tissue) in the hamster cheek pouch to explore the long-term potential inhibitory effect of the same BNCT protocols on the development of second primary tumors from precancerous tissue. Clinically, second primary tumor recurrences occur in field-cancerized tissue, causing therapeutic failure. We performed boron biodistribution studies followed by in vivo BNCT studies, with 8 months follow-up. All 3 BNCT protocols induced a statistically significant reduction in tumor development from precancerous tissue, reaching a maximum inhibition of 77-100%. The inhibitory effect of BPA-BNCT and (GB-10+BPA)-BNCT persisted at 51% at the end of follow-up (8 months), whereas for GB-10-BNCT it faded after 2 months. Likewise, beam-only elicited a significant but transient reduction in tumor development. No normal tissue radiotoxicity was observed. At 8 months post-treatment with BPA-BNCT or (GB-10+BPA)-BNCT, the precancerous pouches that did not develop tumors had regained the macroscopic and histological appearance of normal (non-cancerized) pouches. A potential new clinical application of BNCT would lie in its capacity to inhibit local regional recurrences.

Dosimetry and radiobiology at the new RA-3 reactor boron neutron capture therapy (BNCT) facility: application to the treatment of experimental oral cancer.

The National Atomic Energy Commission of Argentina (CNEA) constructed a novel thermal neutron source for use in boron neutron capture therapy (BNCT) applications at the RA-3 research reactor facility located in Buenos Aires. The aim of the present study was to perform a dosimetric characterization of the facility and undertake radiobiological studies of BNCT in an experimental model of oral cancer in the hamster cheek pouch. The free-field thermal flux was 7.1 x 10(9) n cm(-2)s(-1) and the fast neutron flux was 2.5 x 10(6) n cm(-2)s(-1), indicating a very well-thermalized neutron field with negligible fast neutron dose. For radiobiological studies it was necessary to shield the body of the hamster from the neutron flux while exposing the everted cheek pouch bearing the tumors. To that end we developed a lithium (enriched to 95% in (6)Li) carbonate enclosure. Groups of tumor-bearing hamsters were submitted to BPA-BNCT, GB-10-BNCT, (GB-10+BPA)-BNCT or beam only treatments. Normal (non-cancerized) hamsters were treated similarly to evaluate normal tissue radiotoxicity. The total physical dose delivered to tumor with the BNCT treatments ranged from 6 to 8.5 Gy. Tumor control at 30 days ranged from 73% to 85%, with no normal tissue radiotoxicity. Significant but reversible mucositis in precancerous tissue surrounding tumors was associated to BPA-BNCT. The therapeutic success of different BNCT protocols in treating experimental oral cancer at this novel facility was unequivocally demonstrated.

Microdistributions of prospective BNCT-compound CuTCPH in tissue sections with a heavy ion microbeam.

Microdistributions of the prospective BNCT-compound CuTCPH, a carborane-containing tetraphenylporphyrin with one Cu atom in its molecular structure, have been obtained in tissue sections of different organs of tumor-bearing and normal Syrian hamsters injected with the boron compound by employing a heavy ion microbeam. High resolution X-ray spectroscopy following micro-PIXE (Particle Induced X-ray Emission with micrometer-sized beams) with a focused (16)O ion beam was used. Focusing was performed with a heavy-ion scanning high-precision magnetic quadrupole triplet microprobe. Squamous Cell Carcinomas were induced on the right Cheek Pouch of Syrian Hamsters (HCP), sampled, cryo-sectioned and freeze-dried. Two-dimensional maps of elemental concentration were obtained by scanning the beam over the samples. Very non-uniform Cu concentrations were found in all sections.

In vivo response to the different LET regions of a 55 MeV helium ion beam.

We evaluated the in vivo response to heavy particle irradiation in rat tail epidermis using silver-stained nucleolar organizer regions (AgNOR) as the end-point. The energy degradation of the beam across the circular section of the tail allowed us to study the damage elicited by two different LET regions of a helium beam, i.e. non-Bragg peak (NBP) and Bragg peak (BP), at different sites on the same sample. The tails were locally irradiated with a helium ion beam at different fluences. AgNOR exhibited marked variations between tissue areas only a few micrometers apart within each tail exposed to a given beam fluence. An analysis of the AgNOR variations in NBP and BP areas of tails exposed to different beam fluences revealed a dose-dependent effect. The AgNOR provide quantitative evidence of differential damage in neighboring tissue areas exposed to different LET regions of a helium-ion beam.

Boron neutron capture therapy for the treatment of oral cancer in the hamster cheek pouch model.

We have proposed and validated the hamster cheek pouch model of oral cancer for boron neutron capture therapy (BNCT) studies and shown that boronophenylalanine delivers potentially therapeutic 36.9 +/- 17.5 ppm boron to tumor tissue with tumor:normal tissue and tumor:blood ratios of 2.4:1 and 3.2:1, respectively. Here we report the first evidence of the usefulness of BNCT for the treatment of oral cancer in an experimental model. We assessed the response of hamster cheek pouch tumors, precancerous tissue, and normal oral tissue to boronophenylalanine-mediated BNCT using the thermalized epithermal beam of the RA-6 Reactor at the Bariloche Atomic Center. BNCT leads to complete remission by 15 days posttreatment in 78% of tumors and partial remission in an additional 13% of tumors with virtually no damage to normal tissue.

The hamster cheek pouch as a model of oral cancer for boron neutron capture therapy studies: selective delivery of boron by boronophenylalanine.

Herein we propose and validate the hamster cheek pouch model of oral cancer for boron neutron capture therapy (BNCT) studies. This model serves to explore new applications of the technique, study the biology and radiobiology of BNCT, and assess the uptake of boron compounds and response of tumor, precancerous tissue, and clinically relevant normal tissues. These issues are central to evaluating and improving the therapeutic gain of BNCT. The success of BNCT is dependent on the absolute amount of boron in the tumor, and the tumor:blood and tumor:normal tissue boron concentration ratios. Within this context, biodistribution studies are pivotal. Tumors were induced in the hamsters with a carcinogenesis protocol that uses dimethyl-1,2-benzanthracene and mimics spontaneous tumor development in human oral mucosa. The animals were then used for biodistribution and pharmacokinetic studies of boronophenylalanine (BPA). Blood, tumor, precancerous pouch tissue surrounding tumor, normal pouch tissue, tongue, skin, cheek mucosa, palate mucosa, liver, and spleen, were sampled at 0-12 h after administration of 300 mg BPA/kg. The data reveal selective uptake of BPA by tumor tissue and, to a lesser degree, by precancerous tissue. Mean tumor boron concentration was 36.9 +/- 17.5 ppm at 3.5 h and the mean boron ratios were 2.4:1 for tumor:normal pouch tissue and 3.2:1 for tumor:blood. Higher doses of BPA (600 and 1200 mg BPA/kg) increased tumor uptake. Potentially therapeutic absolute boron concentrations, and tumor:normal tissue and tumor:blood ratios can be achieved in the hamster oral cancer model using BPA as the delivery agent.

Modified silver staining of nucleolar organizer regions to improve the accuracy of image analysis.

Silver staining of nucleolar organizer regions (NORs) and their subsequent quantification by image analysis are used increasingly in human pathological specimens and experimental models. Because certain conditions determined by the type of tissue and/or its fixation render AgNOR segmentation for image analysis difficult due to insufficient contrast or nonspecific silver precipitation, we propose three improvements to the original technique to overcome these difficulties. Pretreatment with 7% nitric acid produced very distinct dark brown images of AgNORs on a yellow background. The gradient of background colors allowed easy discrimination of nucleolar, nuclear and cytoplasmic structures. Seven morphometric parameters related to number, size and shape of AgNORs were evaluated quantitatively by image analysis on sections pretreated with nitric acid and on adjacent sections treated with citrate buffer in a wet autoclave according to the most widely accepted method for image analysis of AgNOR. Both methods yielded similar results. A second improvement was achieved by coating the slides with 7% celloidin solution in ethyl alcohol-ether prior to AgNOR staining and acid pretreatment. This coating prevented nonspecific silver deposition on argyrophilic bacteria and other tissue debris in human vaginal smears that could make visualizing AgNOR sites difficult. Finally, placing sections face down on the staining solution prevents the formation of nonspecific silver precipitates. These procedures can be applied together or separately according to the requirements of the material to be evaluated.

Experimental study to test the potential tumor promotion effect of a tooth bleaching agent.

Carbamide Peroxide is routinely employed as a whitener for tooth enamel. Oral mucosa protection is recommended to avoid inflammatory reactions. Experimental work has demonstrated its irritative effect on gastric mucosa when swallowed. The activity of certain oxidizing agents as tumoral promoters has been demonstrated and associated to their capacity to induce hyperplasia. Within this context it seemed of interest to assess the possible action of carbamide peroxide as a tumoral promoter in oral mucosa with or without a precancerous condition. Its action was tested in 2 models which are highly sensitive to chemical cancerization: a) Dorsum skin or SENCAR mice treated with carbamide peroxide daily or twice a week with or without prior initiation with dimethylbenz(a)anthracene (DMBA). Control mice were submitted to the standard carcinogenesis protocol, i.e. initiation with DMBA and promotion with 12-O-tetradecanoyl phorbol acetate (TPA). b) Hamster cheek pouch submitted to topical application of carbamide peroxide 3 times a week with or without prior initiation with DMBA, hamster cheek pouch submitted to repeated topical application of DMBA as a complete carcinogen: application twice a week in the control group and identical treatment + 1 weekly application of carbamide peroxide to evaluate its capacity to enhance the process. The effects were assessed between 1 and 14 weeks of treatment at different intervals for the different experimental protocols. The control cases exhibited hyperplasia and tumor induction in keeping with the known sequence for both carcinogenesis models. None of the cases revealed a promoter or enhancer capacity of carbamide peroxide. These results indicate the lack of risk involved in the application of carbamide peroxide even in oral mucosa with a precancerous condition due to the action of initiation agents such as tobacco and alcohol.

Experimental study to test the potential tumor promotion effect of a tooth bleaching agent

Carbamide Peroxide is routinely employed as a whitener for tooth enamel. Oral mucosa protection is recommended to avoid inflammatory reactions. Experimental work has demonstrated its irritative effect on gastric mucosa when swallowed. The activity of certain oxidizing agents as tumoral promoters has been demonstrated and associated to their capacity to induce hyperplasia. Within this context it seemed of interest to assess the possible action of carbamide peroxide as a tumoral promoter in oral mucosa with or without a precancerous condition. Its action was tested in 2 models which are highly sensitive to chemical cancerization: a) Dorsum skin or SENCAR mice treated with carbamide peroxide daily or twice a week with or without prior initiation with dimethylbenz(a)anthracene (DMBA). Control mice were submitted to the standard carcinogenesis protocol, i.e. initiation with DMBA and promotion with 12-O-tetradecanoyl phorbol acetate (TPA). b) Hamster cheek pouch submitted to topical application of carbamide peroxide 3 times a week with or without prior initiation with DMBA, hamster cheek pouch submitted to repeated topical application of DMBA as a complete carcinogen: application twice a week in the control group and identical treatment + 1 weekly application of carbamide peroxide to evaluate its capacity to enhance the process. The effects were assessed between 1 and 14 weeks of treatment at different intervals for the different experimental protocols. The control cases exhibited hyperplasia and tumor induction in keeping with the known sequence for both carcinogenesis models. None of the cases revealed a promoter or enhancer capacity of carbamide peroxide. These results indicate the lack of risk involved in the application of carbamide peroxide even in oral mucosa with a precancerous condition due to the action of initiation agents such as tobacco and alcohol.

Experimental study to test the potential tumor promotion effect of a tooth bleaching agent.

Carbamide Peroxide is routinely employed as a whitener for tooth enamel. Oral mucosa protection is recommended to avoid inflammatory reactions. Experimental work has demonstrated its irritative effect on gastric mucosa when swallowed. The activity of certain oxidizing agents as tumoral promoters has been demonstrated and associated to their capacity to induce hyperplasia. Within this context it seemed of interest to assess the possible action of carbamide peroxide as a tumoral promoter in oral mucosa with or without a precancerous condition. Its action was tested in 2 models which are highly sensitive to chemical cancerization: a) Dorsum skin or SENCAR mice treated with carbamide peroxide daily or twice a week with or without prior initiation with dimethylbenz(a)anthracene (DMBA). Control mice were submitted to the standard carcinogenesis protocol, i.e. initiation with DMBA and promotion with 12-O-tetradecanoyl phorbol acetate (TPA). b) Hamster cheek pouch submitted to topical application of carbamide peroxide 3 times a week with or without prior initiation with DMBA, hamster cheek pouch submitted to repeated topical application of DMBA as a complete carcinogen: application twice a week in the control group and identical treatment + 1 weekly application of carbamide peroxide to evaluate its capacity to enhance the process. The effects were assessed between 1 and 14 weeks of treatment at different intervals for the different experimental protocols. The control cases exhibited hyperplasia and tumor induction in keeping with the known sequence for both carcinogenesis models. None of the cases revealed a promoter or enhancer capacity of carbamide peroxide. These results indicate the lack of risk involved in the application of carbamide peroxide even in oral mucosa with a precancerous condition due to the action of initiation agents such as tobacco and alcohol.

AgNOR are sensitive markers of radiation lesions in squamous epithelia.

The possibility of detection of incipient cellular alterations is central to early diagnosis and to clinician's capacity to discriminate between samples that appear similar on routine preparations. We examined the value of silver-stained nucleolar organizer regions (AgNOR) in detecting radio-induced alterations in a model of squamous epithelium biologically similar to oral mucosa. Morphometry of AgNOR has been proven to be of value in the detection of incipient cellular alterations. This method allows for the quantitative evaluation of lesions induced by high doses of radiation long before they become apparent in routine preparations. We herein examine the capacity of AgNOR to reveal the response to low doses of radiation, closer to the therapeutic or accidental dose to which the epithelium of oral mucosa may be exposed.

Early detection of alterations associated to oral cancer.

The model of hamster cheek pouch carcinogenesis closely mimics the development of human oral cancer. The study of the interaction between chemical carcinogens and radiation in the process of oral carcinogenesis is of interest given that the oral cavity is frequently exposed to chemical carcinogens such as alcohol and tobacco and is the route of entry of therapeutic radiation. In this context, markers of incipient alterations associated to a process of malignant transformation would contribute to early diagnosis and follow-up. The aim of the present study was to assess the early changes produced by carcinogenic agents applied separately or combined in a two-stage carcinogenesis protocol in hamster cheek pouch. The cheek pouch of the hamsters was treated with a single dose of radiation (20 Gy) or 7,12-dimethylbenz(a)anthracene (DMBA) as initiating agents and 12-O-tetradecanoylphorbol-13-acetate (TPA) as a promoting agent for 1 or 2 weeks. The end-points chosen to identify early alterations were hyperplastic foci and silver-stained nucleolar organizer regions (Ag NOR). The data show that both markers are useful in the detection of early alterations compatible with a process of malignant transformation.

Early detection of alterations associated to oral cancer

The model of hamster cheek pouch carcinogenesis closely mimics the development of human oral cancer. The study of the interaction between chemical carcinogens and radiation in the process of oral carcinogenesis is of interest given that the oral cavity is frequently exposed to chemical carcinogens such as alcohol and tobacco and is the route of entry of therapeutic radiation. In this context, markers of incipient alterations associated to a process of malignant transformation would contribute to early diagnosis and follow-up. The aim of the present study was to assess the early changes produced by carcinogenic agents applied separately or combined in a two-stage carcinogenesis protocol in hamster cheek pouch. The cheek pouch of the hamsters was treated with a single dose of radiation (20 Gy) or 7,12-dimethylbenz(a)anthracene (DMBA) as initiating agents and 12-O-tetradecanoylphorbol-13-acetate (TPA) as a promoting agent for 1 or 2 weeks. The end-points chosen to identify early alterations were hyperplastic foci and silver-stained nucleolar organizer regions (Ag NOR). The data show that both markers are useful in the detection of early alterations compatible with a process of malignant transformation.

Early detection of alterations associated to oral cancer.

The model of hamster cheek pouch carcinogenesis closely mimics the development of human oral cancer. The study of the interaction between chemical carcinogens and radiation in the process of oral carcinogenesis is of interest given that the oral cavity is frequently exposed to chemical carcinogens such as alcohol and tobacco and is the route of entry of therapeutic radiation. In this context, markers of incipient alterations associated to a process of malignant transformation would contribute to early diagnosis and follow-up. The aim of the present study was to assess the early changes produced by carcinogenic agents applied separately or combined in a two-stage carcinogenesis protocol in hamster cheek pouch. The cheek pouch of the hamsters was treated with a single dose of radiation (20 Gy) or 7,12-dimethylbenz(a)anthracene (DMBA) as initiating agents and 12-O-tetradecanoylphorbol-13-acetate (TPA) as a promoting agent for 1 or 2 weeks. The end-points chosen to identify early alterations were hyperplastic foci and silver-stained nucleolar organizer regions (Ag NOR). The data show that both markers are useful in the detection of early alterations compatible with a process of malignant transformation.