Sex-related differences in risk factors, outcome, and quality of life in patients with permanent atrial fibrillation: results from the RACE II study.

AIMS: Atrial fibrillation (AF) risk factors translate into disease progression. Whether this affects women and men differently is unclear. We aimed to investigate sex differences in risk factors, outcome, and quality of life (QoL) in permanent AF patients. METHODS AND RESULTS: The Rate Control Efficacy in Permanent Atrial Fibrillation (RACE II) randomized 614 patients, 211 women and 403 men, to lenient or strict rate control. In this post hoc analysis risk factors, cardiovascular events during 3-year follow-up (cardiovascular death, heart failure hospitalization, stroke, systemic embolism, bleeding, and life-threatening arrhythmic events), outcome parameters, and QoL were compared between the sexes. Women were older (71 ± 7 vs. 66 ± 8 years, P < 0.001), had more hypertension (70 vs. 57%, P = 0.002), and heart failure with preserved ejection fraction (36 vs. 17%, P < 0.001), but less coronary artery disease (13 vs. 21%, P = 0.02). Women had more risk factors (3.7 ± 1.2 vs. 2.9 ± 1.4, P < 0.001) Cardiovascular events occurred in 46 (22%) women and 59 (15%) men (P = 0.03). Women had a 1.52 times [95% confidence interval (CI) 1.03-2.24] higher yearly cardiovascular event-rate [8.2% (6.0-10.9) vs. 5.4% (4.1-6.9), P = 0.03], but this was no longer significant after adjusting for the number of underlying risk factors. Women had reduced QoL, irrespective of age and heart rate but negatively influenced by their risk factors. CONCLUSION: In this permanent AF population, women had more accumulation of AF risk factors than men. The observed higher cardiovascular event rate in women was no longer significant after adjusting for the number of risk factors. Further, QoL was negatively influenced by the higher number of risk factors in women. This suggests that sex differences may be driven by the greater risk factor burden in women.

When and how to perform venoplasty for lead placement.

Because of the increasing use of cardiac implantable electronic devices (CIEDs) with one or more intracardiac electrodes, the rate of lead failure is increasing. Moreover, upgrade of the CIED frequently is indicated for cardiac resynchronization therapy or other reasons. Both these situations require a new intervention, preferably using ipsilateral venous access. However, venous obstruction after CIED insertion occurs in 10%-20% of patients and poses a major obstacle for implantation of additional leads. Possible solutions include lead extraction, contralateral lead insertion, and venoplasty. Preprocedural venoplasty is associated with the lowest short- and long-term risks. Here we describe a step-by-step approach to this technique, which can be introduced and safely performed in most interventional catheterization laboratories.

Lenient versus strict rate control in patients with atrial fibrillation.

BACKGROUND: Rate control is often the therapy of choice for atrial fibrillation. Guidelines recommend strict rate control, but this is not based on clinical evidence. We hypothesized that lenient rate control is not inferior to strict rate control for preventing cardiovascular morbidity and mortality in patients with permanent atrial fibrillation. METHODS: We randomly assigned 614 patients with permanent atrial fibrillation to undergo a lenient rate-control strategy (resting heart rate <110 beats per minute) or a strict rate-control strategy (resting heart rate <80 beats per minute and heart rate during moderate exercise <110 beats per minute). The primary outcome was a composite of death from cardiovascular causes, hospitalization for heart failure, and stroke, systemic embolism, bleeding, and life-threatening arrhythmic events. The duration of follow-up was at least 2 years, with a maximum of 3 years. RESULTS: The estimated cumulative incidence of the primary outcome at 3 years was 12.9% in the lenient-control group and 14.9% in the strict-control group, with an absolute difference with respect to the lenient-control group of -2.0 percentage points (90% confidence interval, -7.6 to 3.5; P<0.001 for the prespecified noninferiority margin). The frequencies of the components of the primary outcome were similar in the two groups. More patients in the lenient-control group met the heart-rate target or targets (304 [97.7%], vs. 203 [67.0%] in the strict-control group; P<0.001) with fewer total visits (75 [median, 0], vs. 684 [median, 2]; P<0.001). The frequencies of symptoms and adverse events were similar in the two groups. CONCLUSIONS: In patients with permanent atrial fibrillation, lenient rate control is as effective as strict rate control and is easier to achieve. (ClinicalTrials.gov number, NCT00392613.)

Assessment of sex-related differences and outcome in patients who underwent cryoballoon pulmonary vein isolation for atrial fibrillation: an observational cohort study.

OBJECTIVES: Pulmonary vein isolation (PVI) is widely accepted as an effective and safe treatment for symptomatic atrial fibrillation (AF). However, data on sex-related differences and associations with clinical outcome and safety of PVI with cryoballoon ablation are limited. We sought to compare sexrelated efficacy and safety of cryoballoon ablation and identify sex-related associations with clinical outcomes. METHODS AND RESULTS: We included 650 consecutive patients with AF undergoing PVI with cryoballoon ablation at our institution between 2013 and 2017. The efficacy outcome was the first documented recurrence (>30 s) of AF, atrial flutter or atrial tachycardia (AF/AT) or repeat ablation during follow-up, after a 90-day blanking period. The safety outcome was the incidence of periprocedural complications. Mean age of the population was 58±10, and 210 (32.3%) patients were women. Women were older, had a higher body mass index, had more renal dysfunction and less coronary artery disease as compared with men. The rate of AF/AT recurrence was similar between women and men at 12-month follow-up (27.6% vs 24.8%, p=0.445). The incidence of periprocedural complications was higher in women (12.9% vs 4.6%; p<0.001), specifically groin haematomas and phrenic nerve palsy. On multivariate analysis, left atrial volume index (adjusted OR 1.05, 95% CI 1.00 to 1.10; p=0.032) was associated with the incidence of procedural complications in women. For men, no relation with complications could be found. CONCLUSION: The efficacy of cryoballoon ablation was similar between women and men; however, women had a higher risk of procedural complications.

Initial experience with pulsed field ablation for atrial fibrillation.

Introduction: Pulsed field ablation (PFA) was recently introduced for the treatment of symptomatic atrial fibrillation (AF) with the claim of selectively ablating the myocardium while sparing surrounding tissues. We present our initial experience with a PFA catheter for pulmonary vein isolation (PVI) and describe procedural findings and peri-procedural safety of the first 100 patients. Materials and methods: We investigated 100 patients treated for symptomatic AF using the FARAWAVE PFA catheter (Farapulse, Menlo Park, CA, USA) between July 2021 and March 2022. Procedure workflow and electrophysiological findings at the time of ablation, peri-procedural complications, and operator learning curves are described. Results: The mean age of patients was 62.9 ± 9.4 years, 62% were male subjects and 80% had paroxysmal AF. The median CHA2DS2-VASc score was 1.5 (IQR: 1.0-2.0) and the mean left atrial volume index was 35.7 ± 9.6 ml/m2. In 88 (88%) patients, PVI alone was performed and in 12 (12%) patients additional ablation of the posterior wall was performed. 3D-electroanatomic mapping was performed in 18 (18%) patients. Procedures without mapping lasted for 52.3 ± 16.6 min. The mean number of applications per pulmonary vein (PV) was 8.1 ± 0.6. In all patients (100%), all PVs were confirmed to be isolated. The learning curves of the two operators who performed > 20 procedures showed a negligible variation of performance over time and practice did not significantly predict procedure time [Operator 1 (senior): R 2 = 0.034, p = 0.35; Operator 2 (junior): R 2 = 0.004, p = 0.73]. There was no difference between the procedure times between senior and junior operators (Operator 1: 46.9 ± 9.7 min vs. Operator 2: 45.9 ± 9.9 min; p = 0.73). The only complications observed were two cases of bleeding at the site of percutaneous access. Conclusion: Our initial experience shows that use of the PFA catheter for pulmonary vein isolation (PVI) is safe, fast, and easy to learn.

Identifying patients with atrial fibrillation recurrences after two pulmonary vein isolation procedures.

INTRODUCTION: Pulmonary vein isolation (PVI) is an important treatment for atrial fibrillation (AF). However, many patients need more than one procedure to maintain long-term sinus rhythm. Even after two PVIs some may suffer from AF recurrences. We aimed to identify characteristics of patients who fail after two PVI procedures. METHODS AND RESULTS: We included 557 consecutive patients undergoing a first PVI procedure with a second-generation 28 mm cryoballoon. Follow-up procedures were performed using radiofrequency ablation targeting reconnected PVs only. Recurrent AF was defined as any episode of AF lasting >30 s on ECG or 24 hour Holter monitoring performed at 3, 6 and 12 months post procedure. Mean age was 59.1±10.2 years, 383 (68.8%) were male, 448 (80.4%) had paroxysmal AF and the most common underlying condition was hypertension (36.6%). A total of 140/557 (25.1%) patients underwent redo procedure with PVI only. Of these patients 45 (32.4%) had recurrence of AF. These patients were comparable regarding age and sex to those in sinus rhythm after one or two procedures. Multivariate logistic regression showed that non-paroxysmal AF (OR 1.08 (95% CI 1.01 to 1.15), estimated glomerular filtration rate (OR 0.96, 95% CI 0.94 to 0.99), bundle branch block (OR 4.17, 95% CI 1.38 to 12.58), heart failure (OR 4.17, 95% CI 1.38 to 12.58) and Left Atrium Volume Index (OR 1.04, 95% CI 1.01 to 1.08) were associated with AF recurrence after two PVIs. The area under the curve for the identified risk factors was 0.74. CONCLUSIONS: Using a PVI-only approach, recurrence of AF after two AF ablation procedures is associated with more advanced underlying disease and persistent types of AF.

[Methods of health economic evaluation for health services research]. / Methoden der gesundheitsökonomischen Evaluation in der Versorgungsforschung.

On August 30, 2010, the German Network for Health Services Research [Deutsches Netzwerk Versorgungsforschung e. V. (DNVF e. V.)] approved the Memorandum III "Methods for Health Services Research", supported by the member societies mentioned as authors and published in this Journal [Gesundheitswesen 2010; 72: 739-748]. The present paper focuses on methodological issues of economic evaluation of health care technologies. It complements the Memorandum III "Methods for Health Services Research", part 2. First, general methodological principles of the economic evaluations of health care technologies are outlined. In order to adequately reflect costs and outcomes of health care interventions in the routine health care, data from different sources are required (e. g., comparative efficacy or effectiveness studies, registers, administrative data, etc.). Therefore, various data sources, which might be used for economic evaluations, are presented, and their strengths and limitations are stated. Finally, the need for methodological advancement with regard to data collection and analysis and issues pertaining to communication and dissemination of results of health economic evaluations are discussed.

Does intensity of rate control influence outcome in persistent atrial fibrillation? Data of the RACE study.

BACKGROUND: Large trials have demonstrated that rate control is an acceptable alternative for rhythm control. However, optimal heart rate during atrial fibrillation (AF) remains unknown. Aim of this analysis was to compare outcome between rate control > or =80 and <80 beat/min in patients with persistent atrial fibrillation. METHODS: In the RAte Control versus Electrical cardioversion for persistent atrial fibrillation study, 522 patients were included, and 256 were randomized to rate control. This post hoc analysis included patients randomized to rate control. Patients were divided according to their mean resting heart rate during follow-up, <80 beat/min (n = 75) or > or =80 beat/min (n = 139). The end point, a composite of cardiovascular mortality, heart failure, thromboembolic complications, bleeding, pacemaker implantation, and severe drug side effects, was compared between both groups. RESULTS: During follow-up (2.3 +/- 0.6 years), a significant difference between both groups in heart rate was observed (72 +/- 5 vs 90 +/- 8 beat/min; P < .001). Rate control drugs were not significantly different between both groups. New York Heart Association class and fractional shortening remained unchanged in both groups. There were 17 (23%) end points in the low heart rate group and 24 (17%) in the higher heart rate group (absolute difference, 5.4 [-7.3 to 8.2]; P = ns). Independent predictors for the primary end point were coronary artery disease, digoxin use, and interrupted anticoagulation, not high heart rate. Quality of life was comparable in both groups during follow-up. CONCLUSIONS: In patients treated with a rate control strategy, no differences were observed in terms of cardiovascular morbidity, mortality, and quality of life between the observed differences in level of rate control throughout follow-up.

[Comments by the Working Group for Methods of Economic Evaluation in Health Care (AG MEG) to IQWiG's Draft Guidelines "Methods for Assessment of the Relation of Benefits to Costs in the German Statutory Health Care System"]. / Stellungnahme der AG Methoden der gesundheitsökonomischen Evaluation (AG MEG) zu dem Methodenpapier "Methodik für die Bewertung von Verhältnissen zwischen Nutzen und Kosten im System der deutschen gesetzlichen Krankenversicherung" des Instituts für Qualität und Wirtschaftlichkeit im Gesundheitswesen (IQWiG).

Since the coming into force of the GKV-Wettbewerbsstärkungsgesetz ("Act to strengthen competition in the statutory health insurance system") in April 2007, the Gemeinsame Bundesausschuss (G-BA "Federal Joint Committee") can commission the Institut für Qualität und Wirtschaftlichkeit im Gesundheitswesen (IQWiG--Institute for Quality and Efficiency in Health Care") with the assessment of costs and benefits of drugs. In January 2008, IQWiG published a working document for consultation describing the proposed methods for carrying out those evaluations. This commentary by the AG Methoden der Gesundheitsökonomischen Evaluation (AG MEG--"Working Group for methods of economic evaluation in health care") provides a critical appraisal and recommendations for the further development of IQWIG's draft guidelines. The core statements of the commentary are as follows: (1) The draft guidelines are unbalanced. Instead of providing comprehensive methodological guidance for health technology assessment, which is the actual task of IQWiG, they deal predominantly with the methods of technology appraisal which is in the responsibility of the decision-making bodies, i.e. of the G-BA and the Spitzenverband Bund der Krankenkassen ("Central Federal Association of Health Insurance Funds"). (2) IQWiG intends to compare the cost-effectiveness of alternative treatment options only within a given therapeutic area. The rationale for this restriction is not clear, as the decision-makers have to determine ceiling prices across therapeutic areas and diseases and effectively the overall volume of health care expenditure, as well. (3) IQWiG aims at carrying out an economic evaluation only if in a preceding benefit assessment a drug has been judged to be superior. Therefore, it has to be assured that the benefit assessment is performed in such a way that its results may be used for the economic assessment. This requires the application of summary scores for the joint measurement of multidimensional endpoints (as, e.g., QALYs), to evaluate community effectiveness instead of efficacy, and to choose a time horizon that is sufficiently long to reflect any differences in the health benefits between the technologies being compared. Furthermore, the comment hints at some additional problems embodied in the draft guidelines and a number of key methodological issues which are not discussed at all in the working document. In summary, the methods currently proposed by IQWiG are not up to the task of conducting economic evaluations. It is strongly recommended to perform a public consultation process for the revised draft guidelines anew.

Insulin glargine added to therapy with oral antidiabetic agents improves glycemic control and reduces long-term complications in patients with type 2 diabetes - a simulation with the Diabetes Mellitus Model (DMM).

OBJECTIVE: The purpose of this study was to compare the effect of two insulin therapies with respect to long-term complications in type 2 diabetes patients using the Diabetes Mellitus Model (DMM). The therapies under investigation were insulin glargine combined with the oral antidiabetic agents, glimepiride and metformin, (BOT = basal supported oral treatment) and premixed insulin (CT = conventional therapy). METHODS: The DMM predicts complications over a 10-year period using data from published studies. Particular interest is placed on the influence of HbA1c levels related to time. The simulations are based on 10,000 virtual patients taking BOT and CT and the clinical data are based on the results of the LAPTOP study (Lantus + Amaryl + metformin versus premixed insulin in patients with type 2 diabetes mellitus after failing oral treatment pathways) comparing BOT and CT for 24 weeks. The simulations were performed in patients aged 60 A+/- 9 years with type 2 diabetes in which the duration of disease had a baseline of 9 A+/- 7 years. Sensitivity analyses were carried out by changing the response rate of those on BOT, the age of patients and duration of diabetes. RESULTS: The overall relative risk reductions obtained with BOT versus CT for the base case are, 11% for the nervous and vascular systems, 7% for the renal system, 5% for ophthalmic disorders, 3% for the cardiovascular system and mortality and 6% for any kind of event after 10 years. The advantages of BOT were robust to all the changes in the sensitivity analyses. When compared with the base case, the best therapeutic effects were obtained in younger patients who had been diabetic for a shorter period. CONCLUSIONS: Using the DMM data from the LAPTOP study, simulations based on both therapies showed that the BOT regimen provides better glycemic control and reduction in HbA1c thereby leading to a reduction in the long-term complications of diabetes and mortality.

Different classes of EGFR inhibitors may have different potential to improve local tumour control after fractionated irradiation: a study on C225 in FaDu hSCC.

BACKGROUND AND PURPOSE: Previous experiments reported from this laboratory have shown that simultaneous application of the selective epidermal growth factor receptor tyrosine kinase (EGFR-TK) inhibitor BIBX1382BS during fractionated irradiation significantly prolonged growth delay of FaDu human squamous cell carcinoma but did not improve local tumour control. The present study investigates the effect of the EGFR monoclonal antibody (mAb) C225 on local tumour control of FaDu tumours after combined treatment with single dose and fractionated irradiation to address whether different classes of EGFR inhibitors have different potential to improve the outcome of radiotherapy in the same tumour model. MATERIAL AND METHODS: In unirradiated tumours, C225 was given either once or 4 times i.p. to the nude mice. Irradiation experiments were performed with graded single doses under clamp hypoxic conditions or with 30 fractions in 6 weeks with graded total doses under ambient blood flow. C225 was given 6h before or 6 h before and 2, 5 and 7 days after single dose irradiation. During fractionated irradiation C225 was given once per week. Experimental endpoints were tumour growth delay and local tumour control 120 after end of irradiation. RESULTS: C225 treatment resulted in prolongation of tumour growth delay after drug treatment alone as well as after single dose and fractionated irradiation. TCD50 values were reduced from 56.3 Gy [95% CI 50; 62 Gy] after single dose irradiation alone to 46.0 Gy [41;51] (enhancement ratio [ER]=1.22, P<0.01) after 1 C225 injection and 47.7 Gy [44; 51] after 4 injections of the drug (ER=1.18, P=0.06). After fractionated irradiation, tumour control dose 50% (TCD50) was 73.0 Gy [64; 82] in control tumours and 63.1 Gy [57; 69] after simultaneous C225 treatment, corresponding to an ER of 1.2 (P=0.01). CONCLUSION: Treatment of FaDu hSCC with the anti-EGFR mAb C225 resulted in a significant prolongation of tumour growth delay after single dose and fractionated irradiation. In contrast to previous results on the EGFR-TK inhibitor BIBX1382BS, this prolongation of growth delay translated into a slight but significant improvement of local tumour control. The data indicate that different classes of EGFR inhibitors may have different potential to improve the outcome of radiotherapy in the same tumour model.

Repopulation of moderately well-differentiated and keratinizing GL human squamous cell carcinomas growing in nude mice.

PURPOSE: It has been suggested that, reminiscent of the regulated proliferative response of normal squamous epithelium, squamous cell carcinomas that have preserved characteristics of differentiation have a greater repopulation capacity during fractionated irradiation than undifferentiated tumors. The aim of the present study was to investigate repopulation in moderately well-differentiated and keratinizing GL human squamous cell carcinomas in nude mice. METHODS AND MATERIALS: GL human squamous cell carcinomas were transplanted s.c. into the right hind leg of NMRI nu/nu mice. Irradiation was performed with 5.4 Gy fractions under clamp hypoxia or with 2 Gy fractions under ambient conditions. Six, 12, or 18 fractions were given daily, every second day, or every third day. Graded top-up doses were applied under clamp hypoxia to determine the tumor control dose 50% (TCD(50)). A total of 20 TCD(50) assays were performed and analyzed using maximum-likelihood techniques. RESULTS: With an increasing number of daily 5.4 Gy fractions under clamp hypoxia, the top-up TCD(50) values decreased significantly from 50.9 Gy (95% CI: 47, 54) after single doses to 0 Gy after 18 fractions. For the same number of fractions, the top-up TCD(50) increased with increasing overall treatment time. The results are consistent with a constant repopulation rate with a clonogenic doubling time (T(clon)) of 12.7 days (8.6, 16.8). Under ambient blood flow, the top-up TCD(50)s for daily 2 Gy fractions decreased significantly, but were less pronounced than for 5.4 Gy fractions under clamp hypoxia. For a given number of fractions under ambient conditions, the top-up TCD(50)s did not increase significantly with overall treatment time, except for irradiation with 12 fractions in 36 days compared to 12 and 24 days. The T(clon) value from these data was 24.0 days (11.6, 36.4). CONCLUSION: Our data demonstrate a slow but significant rate of repopulation of clonogenic tumor cells during fractionated irradiation of GL human squamous cell carcinomas under clamp hypoxia without indication of a change of the repopulation rate during treatment. Less pronounced repopulation was observed for irradiation under ambient conditions, which might be explained by preferential survival of hypoxic and therefore nonproliferating cells. Taken together with our previous studies on poorly differentiated FaDu tumors (Petersen et al., IJROBP 2001;51:483-493), the results support important heterogeneity of kinetics and mechanisms of repopulation, in particular of the influence of the oxygenation status of surviving clonogenic cells on the repopulation rate during fractionated irradiation, in different experimental squamous cell carcinoma.

Adjuvant inhibition of the epidermal growth factor receptor after fractionated irradiation of FaDu human squamous cell carcinoma.

BACKGROUND AND PURPOSE: Experiments performed by others have shown that inhibition of EGFR before and after single dose irradiation prolonged growth delay and improved local tumour control. This suggests that adjuvant EGFR inhibition can inactivate clonogens that survived irradiation. To test this hypothesis local tumour control was investigated after fractionated radiotherapy and adjuvant EGFR-TK inhibition. MATERIALS AND METHODS: FaDu hSCC xenografts were irradiated with 30 fractions in 6 weeks with total doses of 30-100Gy. After the end of fractionated irradiation, BIBX1382BS was administered daily orally over a time period of 75 days. Tumour volumes were determined two times per week, the volume doubling time during adjuvant treatment was calculated for progressing and recurrent tumours. Local tumour control was investigated 120 days after end of irradiation. RESULTS: Adjuvant BIBX1382BS significantly reduced the tumour growth rate but did not improve local tumour control. The TCD(50) values were 66.1Gy (95% C.I.: 59; 73Gy) after adjuvant BIBX1382BS treatment and 67.9Gy (61; 75Gy) for control tumours (P=0.9). CONCLUSIONS: These data indicate that, although growth of recurrent tumour cells after irradiation is dependent on the EGFR pathway, tumour cells retain their clonogenic potential despite of EGFR inhibition. The results imply also that a decreased tumour growth rate does not necessarily allow conclusions on enhanced inactivation of clonogenic cells when antiproliferative drugs are combined with radiation.

Impact of increased cell loss on the repopulation rate during fractionated irradiation in human FaDu squamous cell carcinoma growing in nude mice.

PURPOSE: To determine the impact of increased necrotic cell loss on the repopulation rate of clonogenic cells during fractionated irradiation in human FaDu squamous cell carcinoma in nude mice. MATERIALS AND METHODS: FaDu tumours were transplanted into pre-irradiated subcutaneous tissues. This manoeuvre has previously been shown to result in a clear-cut tumour bed effect, i.e. tumours grow at a slower rate compared with control tumours. This tumour bed effect was caused by an increased necrotic cell loss with a constant cell production rate. After increasing numbers of 3-Gy fractions (time intervals 24 or 48 h), graded top-up doses were given to determine the dose required to control 50% of the tumours (TCD50). All irradiations were given under clamp hypoxia. RESULTS: With increasing numbers of daily fractions, the top-up TCD50 decreased from 37.9 Gy (95% CI: 31; 45) after single dose irradiation to 14.1 Gy (8; 20) after irradiation with 15 fractions in 15 days. Irradiation with 18 daily 3-Gy fractions controlled more than 50% of the tumours without a top-up dose. After irradiation with six fractions every second day, the top-up TCD50 decreased to 26.9 Gy (22; 32). No further decrease of the TCD50 was observed after 12 and 18 irradiations every second day. Assuming a constant increase of TCD50 with time, the calculated doubling time of the clonogenic tumour cells (Tclon) was 7.8 days (4.4; 11.3). The Tclon calculated for FaDu tumours growing in pre-irradiated tissues was significantly longer (p=0.0004) than the Tclon of 5.1 days (3.7; 6.5) determined under the same assumptions in a previous study for FaDu tumours growing in normal subcutaneous tissues. CONCLUSIONS: Increased necrotic cell loss by pre-irradiation of the tumour bed resulted in longer clonogen doubling times during fractionated radiotherapy of human FaDu squamous cell carcinoma. This implies that a decreased necrotic cell loss might be the link between reoxygenation and repopulation demonstrated previously in the same tumour model.

Differentiation status of human squamous cell carcinoma xenografts does not appear to correlate with the repopulation capacity of clonogenic tumour cells during fractionated irradiation.

PURPOSE: To investigate the magnitude and kinetics of repopulation in a moderately well differentiated UT-SCC-14 human squamous cell carcinoma [hSCC] in nude mice. This question is of interest because clinical data indicate a higher repopulation capacity in those SCC that have preserved characteristics of differentiation, which appears to be in contrast to results on FaDu and GL hSCC previously reported from this laboratory. METHODS AND MATERIALS: UT-SCC-14 tumours were transplanted subcutaneously into the right hind leg of NMRI nu/nu mice. Fractionated radiation treatments were delivered, either under clamped hypoxia at 5.4 Gy/fraction or under ambient conditions (consistent with an OER of 2.7). Tumours were irradiated every day, every 2nd day, or every 3rd day with 6, 12 or 18 fractions. 1, 2 or 3 days after the last fraction, graded top-up-doses under clamped conditions were given for the purpose of estimating the 50% tumour control dose (TCD50). A total of 22 TCD50 assays were performed and analysed using maximum likelihood techniques. RESULTS: The data demonstrate a slow but significant repopulation of clonogenic cells during fractionated irradiation of UT-SCC-14 hSCC. The results under hypoxic conditions are consistent with a constant repopulation rate, with a clonogenic doubling time (Tclon) of 15.6 days (95% CI: 9.7, 21.4). This contrasts with ambient conditions where Tclon was 68.5 days (95% CI: 124, 161). Both Tclon values are longer than the 6-day volume doubling time of untreated tumours. CONCLUSIONS: Less pronounced repopulation for irradiation under ambient compared to clamped hypoxic conditions might be explained by preferential survival of hypoxic and therefore non-proliferating clonogenic cells. Taken together with previous studies on poorly differentiated FaDu and moderately well differentiated GL hSCC, the results are consistent with considerable variability in the magnitude and kinetics of repopulation in different experimental squamous cell carcinomas, and with a relationship between reoxygenation and repopulation during fractionated irradiation. The differentiation status of hSCC growing in nude mice does not to appear to correlate with the proliferative capacity of clonogenic tumour cells during treatment. The results do not support the hypothesis gained from clinical data of higher repopulation in well-differentiated tumours.

Ultrafractionation in A7 human malignant glioma in nude mice.

PURPOSE: Low-dose hyperradiosensitivity (HRS) has been demonstrated in numerous cell lines in vitro, including a number of radioresistant human malignant glioma cell lines such as A7. The aim of our experiment was to show whether HRS can be exploited by using ultrafractionated irradiation (UF) to improve local control of A7 tumours growing in nude mice. Extrapolation of the in vitro results predict a 3.7-fold difference in the efficacy of UF compared with conventional fractionation (CF). MATERIAL AND METHODS: Subcutaneuously growing A7 tumours were irradiated either with UF (126 fractions in 6 weeks, 0.4 Gy per fraction) or CF (30 fractions in 6 weeks, 1.68 Gy per fraction). The total dose was 50.4 Gy in both experimental arms. Fractionated irradiations were given under ambient conditions and followed by graded top-up doses under clamp hypoxia. Endpoints were tumour growth delay and local tumour control 180 days after the end of treatment. RESULTS: UF resulted in a significant decrease of tumour growth delay and in a significant increase of the top-up TCD(50) compared with CF (40.0 Gy [95% CI 29; 61 Gy] versus 28.3 Gy [24; 35 Gy], p=0.047). CONCLUSIONS: Despite a pronounced HRS phenomenon in vitro, UF was significantly less effective than CF in A7 human malignant glioma in nude mice. These results neither disprove the existence of HRS nor do they exclude a possible clinical value of UF. The findings rather indicate that simplistic extrapolation from results obtained after single-dose exposure or few fractions in vitro is not sufficient to predict outcome of UF in vivo and that comprehensive evaluation of novel treatment options in animal models continues to be an essential requirement for clinical translation.