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Biomedical subjects

Johannes H A M Kaanders

Publications and source records attributed to Johannes H A M Kaanders.

At least 19 recordsLinked to original sources
PubMed2007

Effect of routine follow-up after treatment for laryngeal cancer on life expectancy and mortality: results of a Markov model analysis.

BACKGROUND: Routine follow-up is offered to all patients with laryngeal cancer who are treated with curative intent. Although time and resources are devoted to surveillance, the effect of asymptomatic recurrence detection is not well understood. For this study, the authors evaluated the effect that routine follow-up may have on life expectancy and disease-specific mortality rate for patients with laryngeal cancer. METHODS: Using a Markov model, a cohort simulation was performed on 4 hypothetical age groups of patients with laryngeal cancer. Three different follow-up strategies were compared-the current schedule, no follow-up, and the perfect follow-up-in which all recurrences were detected asymptomatically. Sensitivity analyses were performed to study the impact of variations in the transition rates on life expectancy. RESULTS: Compared with no follow-up, the current schedule showed a gain in life expectancy with a range from 0.3 years to 1.5 years that decreased with advancing age. Abolishing the current follow-up schedule raised the disease-specific mortality rate; the increase ranged from 2.8% to 5.9%. Variations of +/-25% in the transition rates produced only a modest effect on life expectancy. CONCLUSIONS: A small reduction in life expectancy was observed when follow-up was withheld from the majority of patients. Disease-specific mortality rates rose when no follow-up was provided. These rates probably were overestimated. A simplified version of the current follow-up protocol may be implemented.

Adult↗
PubMed2007

Screening for local and regional cancer recurrence in patients curatively treated for laryngeal cancer: definition of a high-risk group and estimation of the lead time.

BACKGROUND: All patients treated for laryngeal cancer are offered the same follow-up schedule to detect asymptomatic locoregional recurrences. In this study, we evaluated the prognostic profile of patients for cancer recurrence and estimated the lead time. METHODS: A cohort study was performed between 1990 and 1995. Cox proportional hazards model was used to analyze the prognostic factors. The effect of altering the follow-up for asymptomatic recurrence detection was determined after estimating the lead time. RESULTS: The variables cT classification, smoking, and histologic grade proved to be prognostic factors. The risk of locoregional failure was 15% in the low-risk group versus 29% in the high-risk group. The estimated lead time was 2 to 4 weeks. CONCLUSION: Risk profiles for locoregional relapse were defined. Intensifying the follow-up schedule is not advisable because the lead time is very short. An excessively high number of routine visits would have to be performed to increase the detection rate for asymptomatic recurrences.

Carcinoma, Squamous Cell↗
PubMed2006

Reduced late rectal mucosal changes after prostate three-dimensional conformal radiotherapy with endorectal balloon as observed in repeated endoscopy.

PURPOSE: The aim of this study was to investigate prospectively the rectal wall (Rwall) spatial dose distribution, toxicity, and mucosal changes after prostate cancer radiotherapy with or without an endorectal balloon (ERB). METHODS AND MATERIALS: A total of 24 patients with ERB and 24 without ERB (No-ERB) were treated with three-dimensional conformal radiotherapy (3D-CRT) to a dose of 67.5 Gy. The Rwall was divided into 16 mucosal areas and Rwall dose surface maps were constructed. After 3 months, 6 months, 1 year, and 2 years a rectosigmoidoscopy was performed, and each mucosal area was scored on telangiectasia, congestion, ulceration, stricture, and necrosis. Late rectal toxicity was correlated with the endoscopic findings. RESULTS: The ERB significantly reduced the Rwall volume exposed to doses >40 Gy. Late rectal toxicity (grade >or=1, including excess of bowel movements and slight rectal discharge) was reduced significantly in the ERB group. A total of 146 endoscopies and 2,336 mucosal areas were analyzed. Telangiectases were most frequently seen and appeared after 6 months. At 1 and 2 years, significantly less high-grade telangiectasia (T 2-3) was observed in the ERB group at the lateral and posterior part of the Rwall. In mucosal areas exposed to doses >40 Gy, less high-grade telangiectases (T 2-3) were seen in the ERB group compared with the No-ERB group. CONCLUSIONS: An ERB reduced the Rwall volume exposed to doses >40 Gy, resulting in reduction of late rectal mucosal changes and reduced late rectal toxicity. Although further analysis is needed, these data suggest an ERB-induced increased tolerance for late Rwall damage.

Gastrointestinal Hemorrhage↗
PubMed2006

Microenvironmental transformations by VEGF- and EGF-receptor inhibition and potential implications for responsiveness to radiotherapy.

The microregional distribution and dynamics of tumor cell hypoxia and proliferation are important determinants of tumor aggressiveness and resistance to treatment. Modulation of these elements by biological targeted drugs such as EGFR- and VEGFR-inhibitors may improve the effect of radiotherapy significantly. These combinations are being evaluated in clinical trials and evidence of their effectiveness is accumulating. However, the mechanistic basis of this cooperative effect and the role and behavior of the microregional tumor phenotype under EGF- and VEGF-blockage is poorly understood. Unfolding of these interactions and effects further downstream is necessary to exploit these biological modifiers most profitably to unravel questions such as: (1) can microregional phenotypes be modulated by EGFR- or VEGFR-blockage and how do downstream effects in the signaling pathways relate to these changes? (2) How do the microregional changes induced by EGFR- and VEGF-blockage affect the responsiveness of tumors to ionizing radiation? Answering these questions will improve our understanding of tumor growth related phenotypic transformations at the microregional level and how these can be influenced by modulation of the EGF- and VEGF-signaling pathways. This knowledge can be used to identify and improve therapeutic combinations with the novel biological modifiers and test a variety of biological-based treatment approaches.

Cell Cycle↗
PubMed2006

Derivative-free generation and interpolation of convex Pareto optimal IMRT plans.

In inverse treatment planning for intensity-modulated radiation therapy (IMRT), beamlet intensity levels in fluence maps of high-energy photon beams are optimized. Treatment plan evaluation criteria are used as objective functions to steer the optimization process. Fluence map optimization can be considered a multi-objective optimization problem, for which a set of Pareto optimal solutions exists: the Pareto efficient frontier (PEF). In this paper, a constrained optimization method is pursued to iteratively estimate the PEF up to some predefined error. We use the property that the PEF is convex for a convex optimization problem to construct piecewise-linear upper and lower bounds to approximate the PEF from a small initial set of Pareto optimal plans. A derivative-free Sandwich algorithm is presented in which these bounds are used with three strategies to determine the location of the next Pareto optimal solution such that the uncertainty in the estimated PEF is maximally reduced. We show that an intelligent initial solution for a new Pareto optimal plan can be obtained by interpolation of fluence maps from neighbouring Pareto optimal plans. The method has been applied to a simplified clinical test case using two convex objective functions to map the trade-off between tumour dose heterogeneity and critical organ sparing. All three strategies produce representative estimates of the PEF. The new algorithm is particularly suitable for dynamic generation of Pareto optimal plans in interactive treatment planning.

Algorithms↗
PubMed2006

Imaging hypoxia after oxygenation-modification: comparing [18F]FMISO autoradiography with pimonidazole immunohistochemistry in human xenograft tumors.

PURPOSE: Hypoxia is one of the reasons for radiation therapy resistance. Positron emission tomography using (18)F-labeled misonidazole ([(18)F]FMISO) is a non-invasive method of imaging tumor hypoxia. Aim of this study was to validate [(18)F]FMISO against the clinically most widely used hypoxic cell marker pimonidazole under different oxygenation conditions. MATERIALS AND METHODS: One human head and neck squamous cell carcinoma (SCCNij3) and two human glioblastoma (E102 and E106) xenograft tumor lines were studied after injection of [(18)F]FMISO and pimonidazole. Control mice were compared with a second group breathing carbogen to reduce tumor hypoxia and with a third group with clamped tumors to increase hypoxia. Tumor sections were analyzed on a phosphor imaging system and consecutively stained immunohistochemically (IHC) for visualization of pimonidazole. Pixel-by-pixel analysis was performed and the hypoxic fraction, obtained after segmentation of the pimonidazole signal, was related to the mean optical density of [(18)F]FMISO and pimonidazole. RESULTS: A moderate pixel-by-pixel correlation between [(18)F]FMISO autoradiography and pimonidazole IHC was found for the control tumors, after carbogen breathing and after clamping for SCCNij3. For E102 and E106, mean signal intensities for pimonidazole significantly decreased after carbogen breathing and increased after clamping, mean [(18)F]FMISO signal intensities increased significantly after clamping and a significant correlation between the hypoxic fractions and the mean [(18)F]FMISO signal intensities was found. CONCLUSIONS: [(18)F]FMISO autoradiography and pimonidazole immunohistochemistry can both be used to visualize treatment induced changes in tumor hypoxia. However, the response to these modifications differs widely between xenograft tumor lines.

Animals↗
PubMed2006

Effects of hyperoxygenation on FDG-uptake in head-and-neck cancer.

PURPOSE: Tumor hyperoxygenation results in high response rates to ARCON (accelerated radiotherapy with carbogen and nicotinamide). The effect of hyperoxygenation on tumor metabolism using [(18)F]fluorodeoxyglucose (FDG) positron emission tomography (PET) was investigated. METHODS: Within one week, FDG-PET was performed without and with hyperoxygenation by carbogen breathing and/or nicotinamide administration in 22 patients, eligible for ARCON for head-and-neck cancer. Maximum standardized uptake values (SUV(max)) in both scans and the relative change were calculated in the primary tumor and in normal muscle. RESULTS: Alteration of the tumor oxygenation state induced profound, but variable, metabolic changes (median DeltaSUV(max) -4%; range -61% to +30%). Metabolism in normal muscle was not affected. In three patients who did not achieve local tumor control, the SUV(max) after hyperoxygenation differed less than 5% change as compared to baseline, whereas 13 of the 16 patients with local tumor control showed a larger difference (p<0.05). CONCLUSION: Given the heterogeneous response pattern of nicotinamide and carbogen on FDG-uptake in head-and-neck carcinoma, the prognostic significance of semiquantitative FDG-PET before and after hyperoxygenation remains uncertain and requires confirmation in larger clinical studies before introducing the procedure as a predictive tool for oxygenation modifying treatments.

Aged↗
PubMed2006

The prognostic value of endogenous hypoxia-related markers for head and neck squamous cell carcinomas treated with ARCON.

BACKGROUND AND PURPOSE: Hypoxic radioresistance is an important cause for treatment failure in a number of tumor types including head and neck cancers. Recent studies suggest that outcome can be improved by oxygenation modifying treatments such as ARCON. A robust endogenous marker of hypoxia might be a valuable aid to select patients for such treatments. The aim of this investigation was to study associations between the putative endogenous hypoxia markers CA-IX, Glut-1 and Glut-3 and clinical tumor and patient characteristics and to evaluate the prognostic value of these markers. PATIENTS AND METHODS: Tumor biopsies from 58 patients treated with ARCON in a phase II trial were included. Tumor sections were immunohistochemically stained for CA-IX, Glut-1 and Glut-3. Sections were scored for relative tumor area stained by the markers (CA-IX and Glut-3) and for intensity of staining (Glut-1 and Glut-3). Further, sections were stained for CD34, an endothelial marker to assess microvascular density. RESULTS: Staining of CA-IX and Glut-3 was observed at some distance from vessels and adjacent to necrosis. Glut-1 staining was generally very diffuse. The distribution of clinical characteristics was equal between tumors with high and low marker expression. Significant differences were found for locoregional control (P = 0.04) and for freedom of distant metastases (P = 0.02) in favour of patients with high CA-IX positivity (>25% of tumor area). High Glut-3 expression was associated with a better locoregional control (P = 0.04). Higher Glut-1 intensity was associated with an increased rate of distant metastases (P = 0.0005) and a worse overall survival (P = 0.001). CONCLUSIONS: The inconsistent associations with outcome of CA-IX and the glucose transporters indicate that different factors play a role in up-regulation of these markers. Compared to studies with conventional treatment, the correlation between CA-IX expression and Glut-3 expression and outcome was reversed after treatment with ARCON. This does not support the potential of any of these proteins as very specific and robust hypoxia markers.

Adult↗
PubMed2006

Compliance and efficiency before and after implementation of a clinical practice guideline for laryngeal carcinomas.

We evaluated whether the implementation of a nationwide clinical practice guideline for diagnosis, treatment and follow-up of laryngeal carcinomas led to changes in hospital costs, balanced against clinical changes observed following the guideline's implementation. Charts of 822 patients with larynx carcinoma (459 treated before the introduction of the guideline and 363 thereafter) in five hospitals were retrospectively investigated. In all phases, no differences in total hospital costs were observed after the guideline's implementation. Total mean costs were Euro 3,207 (95%CI 3,091-3,395) for diagnosis, Euro 3,169 (2,153-4,182), Euro 5,026 (3,996-6,057), Euro 6,458 (5,579-7,337), Euro 8,037 (7,469-8,606), Euro 12,765 (10,763-14,769), Euro 19,227 (16,848-21,605) for treatment of dysplasia, carcinoma in situ, T1, T2, T3 and T4 carcinoma, respectively, and Euro 1,856 (1,491-2,220) for 1 year disease-free follow-up. In an earlier study, we observed several positive changes after the guideline's implementation. Balanced against the equal costs before and after the guideline's implementation, we conclude that the efficiency of the care process improved.

Adult↗
PubMed2006

Radiotherapy in the treatment of mucosal melanoma of the upper aerodigestive tract: analysis of 74 cases. A Rare Cancer Network study.

PURPOSE: To retrospectively analyze a series of mucosal melanoma of the upper aerodigestive tract to determine the prognostic factors and contribute to understanding the role of radiotherapy in the therapeutic strategy. METHODS AND MATERIALS: Seventy-four patients were analyzed. The most frequent locations were nasal and oral, in 31 patients (41.9%) and 12 patients (16.2%), respectively. Sixty-three patients (85.1%) were in Stage I, 5 (6.8%) in Stage II, and 6 (8.1%) in Stage III. Treatment consisted of surgery in 17 patients (23.0%), surgery and radiotherapy in 42 (56.8%), radiotherapy in 11 (14.9%), and chemo-immunotherapy in 4 (5.4%). Median follow-up was 20 months. RESULTS: Local control at 3 years was 57% after surgery alone and 71% after surgery and radiotherapy. Overall and disease-free survival rates, respectively, were 41% and 31% at 3 years and 14% and 22% at 10 years. After univariate analysis, female gender, melanosis, tumor size </=3 cm, Stage I, postoperative radiotherapy, and complete remission were favorable prognostic factors. Stage I and melanosis were confirmed by multivariate analysis. CONCLUSIONS: Local control was improved by postoperative radiotherapy, despite survival being as poor as in other published series. Stage I and melanosis at diagnosis were the most favorable prognostic factors.

Adult↗
PubMed2006

Bladder filling variation during radiation treatment of prostate cancer: can the use of a bladder ultrasound scanner and biofeedback optimize bladder filling?

PURPOSE: To investigate the use of a bladder ultrasound scanner in achieving a better reproducible bladder filling during irradiation of pelvic tumors, specifically prostate cancer. METHODS AND MATERIALS: First, the accuracy of the bladder ultrasound scanner relative to computed tomography was validated in a group of 26 patients. Next, daily bladder volume variation was evaluated in a group of 18 patients. Another 16 patients participated in a biofeedback protocol, aiming at a more constant bladder volume. The last objective was to study correlations between prostate motion and bladder filling, by using electronic portal imaging device data on implanted gold markers. RESULTS: A strong correlation between bladder scanner volume and computed tomography volume (r = 0.95) was found. Daily bladder volume variation was very high (1 SD = 47.2%). Bladder filling and daily variation did not significantly differ between the control and the feedback group (47.2% and 40.1%, respectively). Furthermore, no linear correlations between bladder volume variation and prostate motion were found. CONCLUSIONS: This study shows large variations in daily bladder volume. The use of a biofeedback protocol yields little reduction in bladder volume variation. Even so, the bladder scanner is an easy to use and accurate tool to register these variations.

Biofeedback, Psychology↗
PubMed2006

Cancer recurrence after total laryngectomy: treatment options, survival, and complications.

BACKGROUND: A follow-up schedule to detect asymptomatic cancer recurrence is offered to all patients with laryngeal cancer. In this study, the therapeutic options, prognosis, and morbidity of patients with total laryngectomy, who were found to have cancer recurrence during this follow-up schedule were determined. METHODS: Patients who had undergone a total laryngectomy between January 1, 1990, and January 1, 2000, and had cancer recurrence were included. Data from this group were analyzed retrospectively. RESULTS: The prognosis was poor after the development of cancer recurrence. Curative therapy could only be offered to 27.5% of these patients. Only 5% of the patients were disease free at the end of the study period. Many patients with cancer recurrence needed interventions. A large proportion of them had complications. CONCLUSIONS: The follow-up schedule offered to patients after total laryngectomy should put greater emphasis on care than on early detection of cancer recurrence.

Adult↗
PubMed2006

Correction of an image size difference between positron emission tomography (PET) and computed tomography (CT) improves image fusion of dedicated PET and CT.

AIM: Clinical work in software positron emission tomography/computed tomography (PET/CT) image fusion has raised suspicion that the image sizes of PET and CT differ slightly from each other, thus rendering the images suboptimal for image fusion. The aim of this study was to evaluate the extent of the relative image size difference between PET and CT and the impact of the correction of this difference on the accuracy of image fusion. METHODS: The difference in real image size between PET and CT was evaluated using a phantom study. Subsequently, 13 patients with cancer in the head/neck area underwent both CT and [(18)F]fluorodeoxyglucose PET in a custom-made mask for external beam radiotherapy, with multimodality markers for positional reference. The image size of PET relative to CT was determined by evaluating the distances between the markers in multiple directions in both scans. Rigid-body image fusion was performed using the markers as landmarks, with and without correction of the calculated image size difference. RESULTS: Phantom studies confirmed a difference in real image size between PET and CT, caused by an absolute error in PET image size calibration. The clinical scans demonstrated an average relative difference in image size of 2.0% in the transverse plane and 0.8% along the longitudinal axis, the PET images being significantly smaller. Image fusion using original images demonstrated an average registration error of 2.7 mm. This error was decreased to 1.4 mm after size correction of the PET images, a significant improvement of 48% (P<0.001). CONCLUSIONS: A significant deviation in PET image size may occur, either as a real image size deviation or as a relative difference from CT. Although possibly not clinically relevant in normal diagnostic procedures, correction of such a difference benefits image fusion accuracy. Therefore, it is advisable to calibrate the PET image size relative to CT before performing high-accuracy rigid-body image fusion.

Algorithms↗
PubMed2006

Dynamics of hypoxia, proliferation and apoptosis after irradiation in a murine tumor model.

Proliferation and hypoxia affect the efficacy of radiotherapy, but radiation by itself also affects the tumor microenvironment. The purpose of this study was to analyze temporal and spatial changes in hypoxia, proliferation and apoptosis after irradiation (20 Gy) in cells of a murine adenocarcinoma tumor line (C38). The hypoxia marker pimonidazole was injected 1 h before irradiation to label cells that were hypoxic at the time of irradiation. The second hypoxia marker, CCI-103F, and the proliferation marker BrdUrd were given at 4, 8 and 28 h after irradiation. Apoptosis was detected by means of activated caspase 3 staining. After immunohistochemical staining, the tumor sections were scanned and analyzed with a semiautomatic image analysis system. The hypoxic fraction decreased from 22% in unirradiated tumors to 8% at both 8 h and 28 h after treatment (P < 0.01). Radiation did not significantly affect the fraction of perfused vessels, which was 95% in unirradiated tumors and 90% after treatment. At 8 h after irradiation, minimum values for the BrdUrd labeling index (LI) and maximum levels of apoptosis were detected. At 28 h after treatment, the BrdUrd labeling and density of apoptotic cells had returned to pretreatment levels. At this time, the cell density had decreased to 55% of the initial value and a proportion of the cells that were hypoxic at the time of irradiation (pimonidazole-stained) were proliferating (BrdUrd-labeled). These data indicate an increase in tumor oxygenation after irradiation. In addition, a decreased tumor cell density without a significant change in tumor blood perfusion (Hoechst labeling) was observed. Therefore, it is likely that in this tumor model the decrease in tumor cell hypoxia was caused by reduced oxygen consumption.

Animals↗
PubMed2005

Hypoxia in relation to vasculature and proliferation in liver metastases in patients with colorectal cancer.

PURPOSE: To investigate hypoxia measured by pimonidazole binding, glucose transporter 1 (GLUT1) and carbonic anhydrase IX (CA-IX) expression, proliferation, and vascularity in liver metastases of colorectal cancer and to compare GLUT1 and CA-IX expression in corresponding primary tumors. METHODS AND MATERIALS: Twenty-five patients with liver metastases of colorectal cancer, planned for metastasectomy, were included. The hypoxia marker pimonidazole and proliferation marker iododeoxyuridine were administered before surgery. After immunofluorescent staining of the frozen metastases, pimonidazole binding, vascularity, and proliferation were analyzed quantitatively. Thirteen paraffin-embedded primary tumors were stained immunohistochemically for GLUT1 and CA-IX expression, which was analyzed semiquantitatively in primary tumors and corresponding liver metastases. RESULTS: In liver metastases, pimonidazole binding showed a pattern consistent with diffusion-limited hypoxia. The mean pimonidazole-positive fraction was 0.146; the mean distance from vessels to pimonidazole-positive areas was 80 microm. When expressed, often co-localization was observed between pimonidazole binding and GLUT1 or CA-IX expression, but microregional areas of mismatch were also observed. No correlation between the level of pimonidazole binding and GLUT1 or CA-IX expression was observed. In some patients, a large fraction (up to 30%) of proliferating cells was present in pimonidazole-stained areas. Expression of CA-IX in primary tumors and metastases showed a significant correlation, which was absent for GLUT1 expression. CONCLUSIONS: Compared with other tumor types, liver metastases of colorectal cancer contain large amounts of hypoxic cells. The lack of correlation with pimonidazole binding brings into question the value of GLUT1 and CA-IX as endogenous markers of hypoxia.

Adult↗
PubMed2005

Oxygen-modifying treatment with ARCON reduces the prognostic significance of hemoglobin in squamous cell carcinoma of the head and neck.

PURPOSE: To evaluate the prognostic significance of hemoglobin (Hb) levels measured before and during treatment with accelerated radiotherapy with carbogen and nicotinamide (ARCON). METHODS AND MATERIALS: Two hundred fifteen patients with locally advanced tumors of the head and neck were included in a phase II trial of ARCON. This treatment regimen combines accelerated radiotherapy for reduction of repopulation with carbogen breathing and nicotinamide to reduce hypoxia. In these patients, Hb levels were measured before, during, and after radiotherapy. RESULTS: Preirradiation and postirradiation Hb levels were available for 206 and 195 patients respectively. Hb levels below normal were most frequently seen among patients with T4 (p < 0.001) and N2 (p < 0.01) disease. Patients with a larynx tumor had significantly higher Hb levels (p < 0.01) than other tumor sites. During radiotherapy, 69 patients experienced a decrease in Hb level. In a multivariate analysis there was no prognostic impact of Hb level on locoregional control, disease-free survival, and overall survival. Primary tumor site was independently prognostic for locoregional control (p = 0.018), and gender was the only prognostic factor for disease-free and overall survival (p < 0.05). High locoregional control rates were obtained for tumors of the larynx (77%) and oropharynx (72%). CONCLUSION: Hemoglobin level was not found to be of prognostic significance for outcome in patients with squamous cell carcinoma of the head and neck after oxygen-modifying treatment with ARCON.

Administration, Inhalation↗
PubMed2005

Hypoxic cell turnover in different solid tumor lines.

PURPOSE: Most solid tumors contain hypoxic cells, and the amount of tumor hypoxia has been shown to have a negative impact on the outcome of radiotherapy. The efficacy of combined modality treatments depends both on the sequence and timing of the treatments. Hypoxic cell turnover in tumors may be important for optimal scheduling of combined modality treatments, especially when hypoxic cell targeting is involved. METHODS AND MATERIALS: Previously we have shown that a double bioreductive hypoxic marker assay could be used to detect changes of tumor hypoxia in relation to the tumor vasculature after carbogen and hydralazine treatments. This assay was used in the current study to establish the turnover rate of hypoxic cells in three different tumor models. The first hypoxic marker, pimonidazole, was administered at variable times before tumor harvest, and the second hypoxic marker, CCI-103F, was injected at a fixed time before harvest. Hypoxic cell turnover was defined as loss of pimonidazole (first marker) relative to CCI-103F (second marker). RESULTS: The half-life of hypoxic cell turnover was 17 h in the murine C38 colon carcinoma line, 23 h and 49 h in the human xenograft lines MEC82 and SCCNij3, respectively. Within 24 h, loss of pimonidazole-stained areas in C38 and MEC82 occurred concurrent with the appearance of pimonidazole positive cell debris in necrotic regions. In C38 and MEC82, most of the hypoxic cells had disappeared after 48 h, whereas in SCCNij3, viable cells that had been labeled with pimonidazole were still observed after 5 days. CONCLUSIONS: The present study demonstrates that the double hypoxia marker assay can be used to study changes in both the proportion of hypoxic tumor cells and their lifespan at the same time. The present study shows that large differences in hypoxic cell turnover rates may exist among tumor lines, with half-lives ranging from 17-49 h.

Animals↗