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Pain

Chronic postsurgical pain in Europe

An observational study

Fletcher, Dominique*; Stamer, Ulrike M.*; Pogatzki-Zahn, Esther; Zaslansky, Ruth; Tanase, Narcis Valentin; Perruchoud, Christophe; Kranke, Peter; Komann, Marcus; Lehman, Thomas; Meissner, Winfried euCPSP group for the Clinical Trial Network group of the European Society of Anaesthesiology

Author Information
European Journal of Anaesthesiology: October 2015 - Volume 32 - Issue 10 - p 725-734
doi: 10.1097/EJA.0000000000000319
  • Free

Abstract

Introduction

There is widespread acknowledgement that chronic postsurgical pain (CPSP) is a significant medical problem.1,2 It has an estimated mean incidence of 30% that varies according to the definition of CPSP and type of surgery.1,2 CPSP severe enough to result in clinically relevant functional impairment is reported by 5 to 10% of the patients.2 Although multiple approaches to prevent CPSP have been discussed, there is no consensus for an overall effective method for the prevention and treatment of CPSP.2,3 Every year, surgery is performed in over 40 million patients in the European Union. Therefore, the number of patients potentially exposed to CPSP is large and CPSP represents a major, largely unresolved clinical problem.2 Most studies on CPSP have collected data in a single institution, at a national level, enrolled one type of surgery only, included a limited number of patients or used a retrospective design.4 As the generalisation of these results is not feasible, there is a need for prospective observational studies on the incidence and risk factors of CPSP. No prospective data have been collected at a European level involving a large cohort of patients and using the same methodology.

PAIN OUT (http://www.pain-out.eu/) is a multinational research group working on quality improvement of acute postoperative pain management with a collaboration of clinicians, researchers and software engineers.5–7 A standardised postoperative questionnaire has been developed, translated and validated in different European languages.8 A collaboration between the PAIN OUT network and the European Society of Anaesthesiology (ESA) Clinical Trial Network provided an interesting opportunity to collect data on CPSP in a large European registry.

The primary goal of this study was to determine the incidence of CPSP at 12 months after surgery in patients enrolled in different European countries in the European pain registry PAIN OUT and to evaluate this with standardised methodology at day one after surgery. Secondary endpoints were the differences in the incidence and characteristics of CPSP as well as pain-related functional impairment at 6 and 12 months with identification of possible risk factors for CPSP.

Materials and methods

Recruitment of European centres

This prospective observational study assessed the incidence and characteristics of CPSP in different medical centres across Europe. The method and design have been used previously.9 Centres were contacted via the Clinical Trial Network of the ESA. Information was posted on the ESA website and provided to congress participants during the ESA meeting in Helsinki, June 2010. Centres were asked to include patients undergoing elective surgery from July 2011 to December 2012.

Ethical considerations

Approval for the study was obtained from the local ethics committee of participating hospitals. Either oral or written consent was accepted, according to local requirements. Details have been published elsewhere.10

Patients included and evaluation on D1

Patient inclusion criteria in the PAIN OUT registry were as follows: elective surgery; consenting age (18 years in the majority of countries or 16 years in the UK); back on the ward from the postanaesthesia care unit for at least 6 h on the first postoperative day (D1); and agreement to participate in the survey.

At D1, patients filled in the validated International Pain Outcomes questionnaire in their native language.8 Personal and clinical data such as comorbidities, preadmission opioid therapy, peri-operative analgesic use, type of surgery [defined according to the International Classification of Diseases version 9 (ICD9)] and details of anaesthesia were recovered from the medical record by a research assistant and entered into the web-based database.11 A unique code was generated for each patient. The code was used to relate patient data collected on D1 with those collected at 6 and 12 months, but there was no link between this code, the patient's name, the questionnaires or the medical records. After data collection on D1, a patient file was created in the dedicated project website by entering four variables: the patient code generated at D1; his or her personal e-mail; their language; and the date of surgery.

Evaluation at 6 and 12 months after surgery

For participation in the CPSP follow-up, the patients were also required to have a personal e-mail address for automatic electronic follow-up at 6 and 12 months after surgery with a link to the questionnaires. As many patients did not have an e-mail address, follow-up by telephonic interview was added to the original protocol. The 6 and 12 months questionnaires were identical and consisted of the short form Brief Pain Inventory (BPI) to evaluate pain intensity and interference of pain with activities and an interview version of the Douleur Neuropathique en 4 Questions (DN4) to screen for neuropathic pain.12–14 The intensity of pain was measured by an 11-point numerical scale (NRS: 0, no pain, 10, worst possible pain). ‘Mild pain’ referred to an average pain on the BPI questionnaire of 1 to 2, ‘moderate pain’ to an average pain of 3 to 5 and ‘severe pain’ to an average pain at least 6. Three or more positive answers to the seven questions of the interview version of the DN4 defined neuropathic pain.12 Functional impairment was evaluated by the mean score of each seven items in the BPI questionnaire.13

Univariate analysis of risk factors of chronic postsurgical pain

To assess the impact of the type of surgery on the incidence of CPSP, four models were used to group the procedures: model 1: 13 organ-based types of surgery (Table 1); model 2: laparoscopic versus open surgery (cholecystectomy, hysterectomy, colectomy); model 3: orthopaedic, gynaeco-obstetric or visceral procedures; and model 4: orthopaedic versus all other types of surgery.

T1-10
Table 1:
Incidence (95% confidence interval) of chronic postsurgical pain at 12 months according to surgical procedure

Univariate analysis was used to predict CPSP at 6 and 12 months. The definition of ‘Preoperative chronic pain’ was based on existence (’Did you have a persistent painful condition for 3 months or more before coming into hospital for this surgery?’); severity (NRS: 0 to 10) and the location (site of surgery; elsewhere, both) of pain before surgery were also used in the analysis. The time spent in severe pain was evaluated by the following question ‘How often were you in severe pain since your operation? Please circle your best estimate of the percentage of time you experienced severe pain’ on a scale from 0 to 100% labelled with ‘never in severe pain’ for 0% and ‘always in severe pain’ for 100%.

Statistical analysis

Our minimum target was to collect around 1000 complete data sets at 6 and 12 months. With a mean expected moderate to severe CPSP incidence of 15%, this would allow the analysis of roughly 15 risk factors in multivariate analysis. The primary end-point was the incidence of moderate to severe CPSP (NRS ≥3/10) at 12 months using the average pain on the BPI questionnaire (’Please rate your pain by circling the one number that best describes your pain on average’). Secondary outcome measures were the incidence of moderate to severe CPSP at 6 months and neuropathic characteristics and pain interference for patients with CPSP at 6 and 12 months. A data-cleaning plan defined appropriate type or range of answers depending on the variable. Univariate analysis of patient, surgery, anaesthesia and analgesia-related possible risk factors of moderate to severe CPSP at 6 and 12 months was performed with subsequent multivariate logistic regression analysis using variables significantly associated with moderate to severe CPSP in the univariate analysis at the same time point. Hosmer-Lemeshow (H-L) statistics were calculated for evaluating the multivariate logistic regression models at 6 and 12 months. Calibration of the multivariate models was assessed with the Hosmer-Lemeshow goodness-of-fit test. Data are presented as event rate [95% confidence interval (95% CI)], mean (SD) or median (quartile range).

Results

Sample characteristics

Eighty centres expressed interest in participation, but only 24 made an effective start. One stopped prematurely during enrolling on D1 and two were unable to collect any data at 6 or 12 months. From July 2011 to December 2012, patients were recruited in 21 medical centres, from 11 countries (five in Switzerland, three in Germany, two in Italy, Romania, Spain, and Belgium, one in France, Ireland, Moldova, the UK and Ukraine). The questionnaires were available in nine different languages (English, French, German, Italian, Spanish, Serbian, Romanian, Russian and Ukrainian). Figure 1 depicts the flow chart of patient inclusion and follow-up. A total of 3120 patients were included at D1 in PAIN OUT at the first postoperative day and, thus, were eligible to take part in euCPSP. Among those contacted for participation in euCPSP after 6 and 12 months, 1570 (55.2%) and 1328 (44.9%) responded. Due to incomplete or inconsistent data entries, one-third could not be considered for analysis. Finally, complete data sets of 1043 patients (66.4% of the patients responding to the euCPSP questionnaire) at 6 months and 889 (66.9%) at 12 months could be analysed. The mean follow-up rate at M12 across centres was 64.6 ± 30.6%. When referring to the initial population participating in PAIN OUT, 33% at 6 months (1043/3120) and 28% at 12 months (889/3120) were available for analysis.

F1-10
Fig. 1:
Flow chart. Data are expressed as event rate (95% CI).

Eighteen different types of surgery were included with various sample sizes (Table 1). The majority of responders filled in the questionnaires sent by e-mail (63.1 and 66.8% at 6 and 12 months, respectively). Patients contacted by telephone were 9.5 (0.9) years older and underwent different procedures than those contacted by e-mail. Characteristics of patients are presented in Table 2.

T2-10
Table 2:
Personal data of patients enrolled in PAIN OUT at the first postoperative day and at 6 and 12 months after surgery

Incidence of chronic postsurgical pain at 12 months

Crude estimation of chronic postsurgical pain incidence at 12 months

Moderate to severe CPSP at 12 months (primary end point) was reported by 11.8% (9.7 to 13.9) (Fig. 1). Moderate CPSP (NRS of 3 to 5) was observed for 9.6% (7.7–11.7), whereas 2.2% complained of severe CPSP (NRS ≥6). The incidence of CPSP varied depending on the type of surgery (Table 1). Specifically, after some procedures, the incidence of severe CPSP was high, 17% (0 to 38) for open cholecystectomy and 7.9% (2 to 16) for total knee arthroplasty (Table 1).

Univariate analysis of risk factors of chronic postsurgical pain at 12 months

Thirteen variables were included in the univariate analysis: sex; age; existence of chronic pain before surgery; opioid treatment before admission for surgery; type of surgery; (using the four models); type of anaesthesia (general anaesthesia, regional anaesthesia or combined general anaesthesia and regional anaesthesia); ketamine administration intraoperatively; severe pain (percentage of time in severe pain during D1 and worst pain since surgery); and effect of pain-related anxiety at D1.

Due to small numbers of gabapentin and pregabalin administration, only intraoperative ketamine (n = 115) could be used as a variable to investigate the effect of preventive medications on CPSP.15

In the univariate analysis, the variables associated with moderate to severe CPSP at 12 months were type of surgery (models 1, 3 and 4), existence of preoperative pain and severity of postoperative pain on POD1, percentage of time in severe pain and higher anxiety scores (Table 3). Intraoperative administration of ketamine or intraoperative regional anaesthesia had no prophylactic effects on the development of CPSP at 12 months.

T3-10
Table 3:
Univariate analysis of risk factors of moderate to severe chronic postsurgical pain at 6 and 12 months

For surgical model 2, open cholecystectomy, hysterectomy and colectomy were not associated with an increased risk of moderate to severe CPSP compared with respective laparoscopic procedures. There is a trend towards reduced moderate to severe CPSP incidence for laparoscopic cholecystectomy (8.8%) versus open cholecystectomy (28%) (Table 1).

In model 3, orthopaedic surgery was associated with a 2.40 increased risk for moderate to severe CPSP at 12 months in comparison to visceral surgery, whereas gynaeco-obstetrical surgery did not result in an increased risk (Table 3). In model 4, orthopaedic surgery was associated with an almost three-fold increased risk for moderate to severe CPSP compared with all other procedures at 12 months.

Patients with preexisting chronic pain before surgery had a 2.6 times higher risk of experiencing moderate to severe CPSP at 12 months than patients with no preoperative pain [odds ratio (OR) 2.63, P < 0.001]. Neither severity nor location of preoperative chronic pain (pain elsewhere, site of surgery or both) was associated with an increase in the incidence of moderate to severe CPSP.

Multivariate analysis of risk factors of chronic postsurgical pain at 12 months

Variables associated with moderate to severe CPSP in the univariate analysis at 12 months were used for subsequent multivariate analysis (Table 4). We chose model 4 (i.e. orthopaedic versus other surgery) to evaluate the impact of the type of surgery, as it was the most stable surgical predictor at both 6 and 12 months. The three risk factors at 12 months were existence of chronic preoperative pain; type of surgery; and percentage of time in severe pain. The OR for time in severe pain was 1.33, indicating that the risk for CPSP increased by 33% if the percentage of time in severe pain increased by 10% (Fig. 3).

T4-10
Table 4:
Multivariate analysis of risk factors of moderate to severe chronic postsurgical pain at 6 and 12 months
F2-10
Fig. 3:
The variation in incidence of moderate to severe chronic postsurgical pain at 6 and 12 months depending on the percentage of time in severe pain at D1. For the time in severe pain, the patients were asked the following question ‘How often were you in severe pain since your surgery? Please circle your best estimate of the percentage of time you experienced severe pain’ on a scale from 0 to 100% labelled with ‘Never in severe pain’ for 0% and ‘always in severe pain’ for 100%. Values are presented as percentages.

Chronic postsurgical pain incidence at 6 months

The incidence of moderate CPSP at six months was significantly higher (13.1%, 11.1 to 15.4; P < 0.001) than the incidence of moderate CPSP at 12 months. The risk difference of moderate pain (6 versus 12 months) is 3.6% (0.8 to 6.4%). For 701 patients, complete data at 6 and 12 months were available. Of the patients with complete data and CPSP at 6 months (n = 63), 55.8% were pain-free at 12 months. A few patients (n = 20; 2.9%) had no CPSP at 6 months but developed CPSP at 12 months.

In univariate analysis, similarly to CPSP at 12 months, type of surgery (models 1, 3 and 4), existence of preoperative pain and severity of postoperative pain on POD1 were identified as risk factors. Male sex was associated with CPSP at 6 months (Table 3). In multivariate analysis, similarly to CPSP at 12 months, the three risk factors were existence of chronic preoperative pain, type of surgery and percentage of time in severe pain.

Chronic postsurgical pain characteristics and consequences

Neuropathic characteristics

Signs of neuropathic pain at 6 and 12 months, respectively, for mild CPSP were reported in 16.3% (11.4 to 22.1) and 16.3% (10.8 to 22.9), for moderate CPSP in 31.3% (2.8 to 40.7) and 35.4% (23.9 to 48.3) and for severe CPSP in 30.4% (13.2 to 53.0) and 57.1% (30.7 to 83.4). Patients with mild CPSP have a significantly lower frequency of neuropathic characteristics than those with moderate CPSP (P = 0.02 at 6 months and P = 0.03 at 12 months, respectively).

Functional impairment

The results of the BPI revealed that patients suffering from severe CPSP reported that pain interfered more with activities and mood both at 6 and 12 months than patients with moderate CPSP. This difference was significant for all BPI items at 6 and 12 months (P < 0.05). Figure 2 displays the data at 12 months.

F3-10
Fig. 2:
Brief Pain Inventory values at 12 months in (a) patients with moderate chronic postsurgical pain and severe CPSP and (b) patients with neuropathic and nonneuropathic moderate to severe CPSP. The seven items of the BPI are pain-related impairment of enjoyment of life, general activity, mood, normal activity, relation to other persons, sleep and walking ability. The data are expressed as box plots (medians, quartile range, 95% percentiles; aoutliers, bextreme outliers). For all BPI items, values were significantly higher for severe CPSP than moderate CPSP and higher for moderate to severe CPSP with neuropathic characteristics than CPSP without neuropathic characteristics (P < 0.01).

Patients with moderate to severe CPSP with neuropathic characteristics had a more pronounced functional impairment than patients with non-neuropathic CPSP. This increased functional impairment was significant for all items of the BPI questionnaire at 6 and 12 months (P < 0.001). Figure 2 displays the data at 12 months.

Discussion

In this study, the development of CPSP was investigated prospectively for the first time using a large European pain registry. The results provide information on the incidence and characteristics of CPSP in Europe on a multicentre level. Although the impact of preoperative chronic pain and the type of surgery have been previously described, a new risk factor associated with the development of CPSP, a high percentage of time in severe pain during the first 24 h, was identified.

European registry on chronic postsurgical pain

This survey of CPSP was developed in association with PAIN OUT network, the largest international registry of acute postoperative pain.5–8 The participating centres in 11 different European countries were able to collect prospective data from 889 patients 12 months after surgery using validated questionnaires. Data were collected without additional dedicated manpower through electronic communication, representing a new approach for a prospective European CPSP study. All participants with an e-mail account automatically received the 6 and 12 month questionnaires and returned the data electronically. A 50% response rate before data cleaning supports the feasibility of such an approach. It compares favourably with a national study in a country with a well established culture of medical data collection that achieved a 65% response rate after postal follow-up.16 The superior cost-effectiveness of digital questionnaires, when used to perform scientific surveys, has been recently confirmed in a study of several hundred patients.17 The PAIN OUT registry with its D1 questionnaire already facilitates local quality improvement through benchmarking using confidential subanalysis. In the future, such a large registry may offer further comparisons concerning the development of CPSP.

Incidence of chronic postsurgical pain

In a large sample of European patients, the mean incidence of moderate to severe CPSP at 12 months after surgery was 11.8%. The 2.2% incidence of severe CPSP at 12 months was low, as has been reported previously.18 The present findings confirm that although the incidence of CPSP can be high when any type of pain is considered, it is less frequent when restricted to moderate to severe CPSP.1,2 This suggests that the conflicting data regarding its incidence might be partially explained by varying definitions of CPSP.1,19 Our results also indicate that the incidence of moderate CPSP declines between 6 and 12 months, confirming a tendency already described between 3 and 6 months after surgery,18 in contrast to some other reports.20 This differs from severe CPSP wherein the incidence appears stable suggesting a potential for long-lasting evolution. Of those patients who did not indicate pain at 6 months, very few reported CPSP at 12 months after surgery. This underlines the importance of repetitive evaluation in understanding the time course of CPSP.

Characteristics and consequences of chronic postsurgical pain

The present findings confirm that up to a half of patients with CPSP have some signs of neuropathy.18 This neuropathic component was more frequent in patients reporting moderate CPSP than those with mild CPSP. This is in line with previous studies that enrolled patients suffering from chronic pain and specifically those involving CPSP.16,18,21

An important recommendation is that the functional impairment caused by CPSP is assessed to give the full picture of disability.1,22 Our results revealed that both pain-related functional and affective interference with activity increased as CPSP became more severe and was stable at 6 and 12 months. CPSP with neuropathic characteristics was also associated with a more pronounced functional impairment. This is in line with previous publications describing the specific burden of neuropathic pain in patients with chronic pain.21

Type of surgery and risk of chronic postsurgical pain

In contrast to reports, thoracotomy was not associated with frequent severe CPSP, but this might be explained by our small sample size. In line with previous findings, the surgical approach for hysterectomy (abdominal, vaginal or laparoscopic) was not associated with CPSP23 and a reduced moderate to severe incidence of CPSP was confirmed for laparoscopic (8.8%) versus open cholecystectomy (28%).18 Orthopaedic surgery was clearly associated with a high incidence of CPSP and preoperative chronic pain proved to be an independent risk factor. Both these findings were particularly true for spine surgery, knee arthroscopy and total knee and total hip arthroplasty (incidence of moderate to severe CPSP at 12 months up to 39.1%). This raises the question of whether CPSP should be included in the preoperative risk–benefit evaluation of orthopaedic procedures such as arthroscopy or knee surgery.24,25

Predictive model of chronic postsurgical pain

In addition to previously reviewed risk factors associated with the patient and surgery,2 a model that included treatment-related factors was also used. The limited power of the present sample precludes any reliable conclusion on the failure to observe preventive effects of ketamine. Our results confirm that the existence of chronic preoperative pain and the severity of postoperative pain are important variables associated with CPSP.2,22,26 Preexisting preoperative pain was associated with a 2.6 times higher risk of CPSP. In contrast to a previous study, localisation of preexisting pain had no influence on the development of CPSP.27 Although postoperative pain played a role as a risk factor, it was not the magnitude of the pain scores but the ‘percentage of time in severe pain’, which multivariate analysis proved to be predictive for CPSP, something described by several authors.2,28 High pain scores may only reflect patient susceptibility derived from factors such as genetic predisposition, psychological variables or individual efficiency of conditioned pain modulation.29,30,31 Prolonged periods of severe postoperative pain may also lead to central sensitisation contributing to the development of CPSP.32 The present results highlight the potential unfavourable consequences of a prolonged period of severe acute pain after surgery and the necessity of its prevention. Each 10% increase in percentage of time in severe pain after surgery was associated with a 30% increase in the incidence of CPSP. These findings emphasise the impact of the duration of postoperative pain and the importance of adequate pain control before and after surgery. Management of pain in patients, especially those undergoing minor surgery, should be taken seriously and special attention has to be paid to this patient cohort largely ignored by an acute pain service.33

Methodological limitations

Colleagues from several hospitals who initially expressed interest in this trial subsequently found themselves unable to meet the demands of enrolment. It is possible that our investigation might not be representative of European hospitals in general, and bias might have occurred. The participation of hospitals might have been driven by their desire to improve their postoperative pain management. Varying numbers of patients were enrolled by the centres and the significant amount of incomplete data sets might be due in part to the web-based questionnaires filled in by the patients without support from a research team. Bias arising from this rate of nonresponders cannot be excluded and may have exposed results to either overestimation or underestimation. Furthermore, the coded registry data made it impossible to make good absent data, leading to exclusion of cases with missing or inconsistent entries. As data collection was restricted to patients back on the ward on the first postoperative day, the results were not applicable to other patient groups. We did not perform a subgroup analysis for factors such as regional anaesthesia, timing of ketamine administration or the 14 surgical models, as heterogeneity, bias and lack of power would have precluded reliable results. We had no further information on the possibility of repeat surgery, although it is reasonable to consider it a rare occurrence. The lack of clinical examination to fully evaluate the characteristics of CPSP might also be a point of discussion.4 However, the DN4 questionnaire has seen much use in large nationwide surveys estimating the prevalence of neuropathic pain in patients suffering from chronic pain as well as CPSP.13,18

Conclusion

Our findings generate new hypotheses that have to be confirmed by further research. An incidence of 11.8% for moderate to severe CPSP 12 months after surgery was revealed with neuropathic signs in 39.2%. Persistent functional impairment correlated with CPSP severity and neuropathic characteristics. The percentage of time in severe pain during the first 24 h after surgery is a new risk factor for CPSP and offers a new management goal in its prevention. This study supports further development of a web-based European registry on CPSP.

Acknowledgements relating to this article

Assistance with the study: we want to thank the European Society of Anaesthesiology for helping in this research project through administrative support of the Clinical Trial Network. The authors are especially grateful to Brigitte Leva Research and the Clinical Trial Coordinator in the European Society of Anaesthesiology. We thank Claudia Weinmann (Department of Anaesthesiology and Intensive Care Medicine, Jena University Hospital, Germany) for her assistance. Thanks are also due to Prof. Dr Andreas Hoeft (Bonn, Germany) Past Chairperson of the ESA Research Committee and the ESA CTN) for his help and support. We are grateful to all the investigators involved in data collection.

Financial support and sponsorship: PAIN-OUT has received funding from the European Community's Seventh Framework Programme FP7/2007–2013 under Grant Agreement No. 223590. The European Society of Anaesthesiology (ESA) sponsored and funded euCPSP with a grant from the ESA-Clinical Trial Network.

Conflicts of interest: none.

Presentation: these data were submitted as a poster abstract to the Euroanesthesia 2015 Berlin.

List of collaborating investigators in the euCPSP group: P Lavand’homme (Cliniques Universitaires Saint-Luc, Brussels, Belgium), M Vercauteren (Universiteit Antwerpen; Belgium), D Fletcher (Hôpital Raymond Poincaré, Garches, France), P Kranke (Universitätsklinikum Würzburg, Germany); W Meissner (Universitätsklinik Jena, Germany); E Pogatzki-Zahn (Universitätsklinik Münster, Germany), G Iohom (Cork University Hospital, Cork, Ireland); G Cinnella (Policlinico ’Ospedali Riuniti, Foggia, Italy), C Aurilio (Seconda Università degli Studi di Napoli, Italy); A Belii (National Scientific and Practical Center for Emergency Medicine, Chisinau, Moldova), D Filipescu (Emergency Institute Prof. Dr CC Iliescu; Bucharest, Romania), NV Tanase (Central University and Emergency Military Hospital Dr Carol Danila, Bucharest, Romania), U Stamer Inselspital, University of Bern, Switzerland), B Rehberg-Klug (Hôpitaux Universitaires de Genève, Switzerland), I Decostered, MR Suter (Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland), C Perruchoud (EHC Hôpital de Morges and University Hospital Center of Lausanne, Lausanne, Switzerland), S Blumenthal (Stadtspital Triemli, Zürich, Switzerland), M Puig (Hospital del Mar; Barcelona, Spain), A Garcia-Filoso (Hospital Universitario San Juan, Alicante, Spain), B Brandner (University College London Hospitals, UK), AM Varvinskiy (Torbay Hospital; Torqay, UK); I Lisnyy (National Cancer Institute, Kiev; Ukraine), I Kuchyn (City Clinical Hospital, Kiev, Ukraine).

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