A Prospective, Comparative Study on Robotic Versus Open-Surgery Hysterectomy and Pelvic Lymphadenectomy for Endometrial Carcinoma

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1 ORIGINAL STUDY A Prospective, Comparative Study on Robotic Versus Open-Surgery Hysterectomy and Pelvic Lymphadenectomy for Endometrial Carcinoma Saskia Eklind, MD, PhD,* Anna Lindfors, MD,* Per Sjöli, BBA,Þ and Pernilla Dahm-Kähler, MD, PhD* Objectives: The aim of this study was to compare surgical outcome, patient recovery, and costs between robot-assisted laparoscopy and laparotomy in women undergoing hysterectomy, bilateral salpingo-oophorectomy (BSOE), and pelvic lymphadenectomy for endometrial carcinoma. Methods: Women undergoing hysterectomy, BSOE, and pelvic lymphadenectomy for endometrial carcinoma, according to regional guidelines, were prospectively, concurrently, and consecutively included from September 2010 to December Surgical outcomes such as operative time, estimated blood loss (EBL), number of lymph nodes retrieved, and complications were analyzed together with hospital stay, days until normal active daily living was retrieved, patient satisfaction with the length of the hospital stay, and cost per patient. Robot-assisted laparoscopy was performed on all cases at the Sahlgrenska University Hospital, and laparotomy was performed on all cases at 3 regional hospitals. Results: Forty women underwent robot-assisted laparoscopy, and 48 underwent laparotomy. There were no differences in age, body mass index, histology, or retrieved lymph nodes. Operative time was significantly shorter in the robot-assisted laparoscopy group (P G ). The EBL was lower and hospital stay was shorter in the robot-assisted laparoscopy group (P G ). There was no statistical difference in complications between the groups, and both groups found hospital stay duration satisfactory. In the robot-assisted laparoscopy group, active daily living was normal within 5 days postoperatively, compared with 14 days in the laparotomy group (P G ). Calculated costs per treated patient did not differ statistically between the groups. Conclusions: Compared with laparotomy and robot-assisted laparoscopic hysterectomy, BSOE pelvic lymphadenectomy for endometrial carcinoma was associated with significantly shorter operative time, hospital stay, and lower EBL. Patients recovered more quickly after robot-assisted laparoscopy, with equal costs number of retrieved lymph nodes, compared with laparotomy. Key Words: Robotic surgery, Endometrial cancer, Patient satisfaction, Cost, Surgical outcome Received March 18, 2014, and in revised form October 20, Accepted for publication December 7, (Int J Gynecol Cancer 2015;25: 250Y256) *Department of Obstetrics and Gynecology, Sahlgrenska University Hospital, Sahlgrenska Academy, Gothenburg; and Regional Cancer Center West, Gothenburg, Sweden. Copyright * 2015 by IGCS and ESGO ISSN: X DOI: /IGC Address correspondence and reprint requests to Saskia Eklind, MD, PhD, Department of Obstetrics and Gynecology, Sahlgrenska University Hospital, Sahlgrenska Academy, SE Gothenburg, Sweden. saskia.eklind@vgregion.se. The study was funded by grants from the Hjalmar Svensson Foundation. The authors declare no conflicts of interest. 250 International Journal of Gynecological Cancer & Volume 25, Number 2, February 2015

2 International Journal of Gynecological Cancer & Volume 25, Number 2, February 2015 Robotic Versus Open-Surgery ndometrial carcinoma is a common cancer among women E worldwide. It is the fifth most common cancer form among women in Sweden and the fourth in the United States. 1,2 The incidence of endometrial carcinoma is increasing, probably due to lifestyle changes associated with elevated body mass index (BMI). 2 It is well known that endometrial carcinoma correlates with high BMI, 3Y5 which in turn places high demands on all treatment modalities. Several studies show that high BMI is associated with increased morbidity during laparotomy as well as postoperatively. 6,7 Minimally invasive surgical techniques, such as laparoscopy, have been shown to be associated with less morbidity in morbidly obese women with endometrial carcinoma. However, there are also reported conversion rates, up to 8% to 30%, to laparotomy due to surgical complexity with laparocopy. 8,9 Since 2005, there has been a steep increase in robot-assisted laparoscopy in gynecological surgery because this technique facilitates minimally invasive surgery in deep, narrow spaces such as the pelvic cavity. Elderly women, particularly those with high BMI, benefit from robot-assisted laparoscopy because it is less invasive and entails shorter time to recovery; the technique is thus increasing in the surgical treatment of endometrial carcinoma. 10,11 It is quite clear that most patients benefit from minimally invasive surgery such as laparoscopy, but the conventional laparoscopic technique has its limitations in more difficult procedures and areas such as lymphadenectomy, which has been facilitated by the introduction of robotic surgery. Several studies present robotic-assisted laparoscopic surgical outcome, but few compare patient satisfaction, recovery time to normal active daily living (ADL), or the absence of severe sequelae. A short recovery time to normal ADL is important for quality of life, and because women with endometrial carcinoma often are elderly, a minimum of surgical trauma increases the possibility to shorten the recovery period. 12,13 The costs associated with robot-assisted laparoscopy have been the subject of intense debate. Some studies report increased costs, compared with laparotomy and traditional laparoscopy, indicating that robot-assisted laparoscopy is not justifiable from an economic perspective. 14Y16 Ithasalsobeenshowninsome studies that robot-assisted laparoscopy is more time consuming than laparotomy, contributing to increased costs. 14,17 Furthermore, it has recently been shown in a benign setting that robotic surgery is more expensive than laparoscopy. However, the cost decreases with increased procedure volume suggesting that the surgeons skills and experience are of importance. 18 In Sweden, patients with endometrial carcinoma are recommended hysterectomy, bilateral salpingo-oophorectomy (BSOE), and aortic or/and pelvic lymphadenectomy. 19 Until the introduction of robotic surgery, laparotomy was the main procedure for patients undergoing lymphadenectomy, and conventional laparoscopy has not been the standard procedure because of its complexity and long learning curve. During the last 3 years, in the Western Sweden Health Care Region, the proportion of minimally invasive surgery for endometrial carcinoma, when pelvic lymphadenectomy is indicated, has increased from 3% to 40%, whereas laparotomy has declined correspondingly due to the introduction of robotic surgery. This indicates that the 2 major surgical procedures for endometrial carcinoma, when lymphadenectomy is included, are laparotomy and robot-assisted laparoscopy. Our aim was to undertake a prospective observational study in women with endometrial carcinoma undergoing hysterectomy, BSOE, and pelvic lymphadenectomy and evaluate surgical outcome, patient satisfaction with the length of the hospital stay, recovery time, and costs comparing robot-assisted laparoscopytolaparotomy. MATERIALS AND METHODS The Western Sweden Health Care Region has approximately 1.7 million inhabitants. There is 1 university hospital, Sahlgrenska University Hospital, and 4 regional hospitals that offer surgical treatment for women diagnosed with gynecologic cancer. Sahlgrenska University Hospital is the referral center for primary surgery in women with vulvar, cervical, and advanced ovarian carcinoma. Women with endometrial cancer are treated at all hospitals in the region. Three of the 4 regional hospitals that treat women with endometrial carcinoma participated in the study, and these participating hospitals do not have access to a Da Vinci system, and women thus undergo laparotomy when the procedure includes pelvic lymphadenectomy. At Sahlgrenska University Hospital, all women with endometrial cancer undergo robotassisted laparoscopy. Endometrial carcinoma was diagnosed after a standard endometrial biopsy or curettage complemented by a transvaginal ultrasound. All women with stage I endometrial carcinoma were recommended hysterectomy and BSOE, and the further extent of the surgical procedure was determined depending on the presence of risk factors, according to the regional guidelines from Stage I endometrial carcinoma cases were divided into low-risk, intermediate-risk, or high-risk groups. When one of the following preoperative risk factors was fulfilled: myometrial invasion more than 50%, aneuploidy, presence of the tumor suppressor marker p53, or grade 3, the woman was categorized in intermediate-risk group, and pelvic lymphadenectomy was recommended and performed in addition to hysterectomy and BSOE. If there were 2 or more risk factors presented, the woman was categorized into the high-risk group and was recommended a hysterectomy, BSOE, and Tomentum resection followed by adjuvant chemotherapy and radiotherapy. New national guidelines were introduced in 2013 with a paradigm shift to pelvic and para-aortic lymphadenectomy in high-risk patients, and only hysterectomy and BSOE were recommended in the other risk groups. The study started in September 2010 and ended in December 2012 due to the new national guidelines and recommendations. The ethics committee at the University of Gothenburg approved the study, and all participants gave their informed consent. All eligible patients were offered to participate in the study, and all accepted. Patients were included concurrently and consecutively at each site. Two gynecologic oncologists performed all laparotomies at each regional hospital; thus, a total of 6 gynecologic oncologists performed these procedures at the Sahlgrenska University Hospital, and 2 gynecologic oncologists performed all procedures with the Da Vinci system. The gynecologic oncologists participating in the study, all centers included, are experienced, and each surgeon has over 10 years of training in gynecological cancer surgery. The patient volume may differ * 2015 IGCS and ESGO 251

3 Eklind et al International Journal of Gynecological Cancer & Volume 25, Number 2, February 2015 between the settings over the years, but the gynecologic oncologists involved are considered to be experienced. The same study protocol was used at all hospitals. Demographics and Surgical Outcome Demographics, including age, BMI, and histology grade, were registered, as was surgical outcome, that is, operative time, estimated blood loss (EBL), and length of hospital stay. For both laparotomy and robot-assisted laparoscopy, operative time was recorded from skin incision to skin closure. The time for the anesthetic procedures before or after surgery has not been included in any of the groups in this study. The experience of the anesthetists setting varies highly in each surgical procedure due to doctors and nurses in training programs. After pathology analysis, the number of retrieved lymph nodes was registered in the study protocol. The t testwasusedtocompareage,thepearsonw 2 test was used to compare histology, and the Mann-Whitney U test was used to compare BMI between robotic-assisted laparoscopy and laparotomy cohorts. Complications Complications were registered separately as intraoperative and early postoperative complications during the hospital stay or as late postoperative complications occurring within 30 days after discharge from the hospital. The patient s records were scrutinized retrospectively to see whether she had been readmitted, and late postoperative complications were identified and registered. Patient Satisfaction Concerning Length of Hospital Stay and Recovery Time Participants responded to a telephone questionnaire 6 to 12 weeks postoperatively. All interviews were conducted by one of the participating doctors. The questionnaire inquired whether they were satisfied with the duration of their hospital stay or not and to define the exact number of days it had taken to recover to normal activities of daily living such as eating, bathing, dressing, toileting, transferring (walking), and continence after surgery. Cost Calculations There is a case-costing system in the Western Sweden Health Care Region, implemented since the middle of the 1990s. The system continually registers patient-related costs for every care episode in the hospital. The total costs for all patients included in the study were compiled and analyzed based on this case-costing system, according to which costs for surgery are based on cost of actual operative time as well as costs for surgeons, surgical staff, anesthetic staff, and pharmaceuticals. In summary, all costs are registered individually in the case-cost system and include total operating time and all activities performed in the operating theater, postoperative monitoring used, complications that initiates costs (such as investigations, imaging, or reoperations), and total hospital stay. The additional costs for robotic surgery not included in the case-costing system, such as the 4-arm robot draping, the assistant port (Kii Optical, Access System, mm; Applied Medical), and a reinsertable lymph node retrieval bag, were added to the other costs. Furthermore, costs for ward care and all 252 associated costs during the hospital stay, such as any additional radiology, laboratory, and medication costs, were also included. The case-costing system automatically registers costs for complications during hospital stay and distinguishes costs for patients with comorbidity. In an attempt to present costs as accurately as possible, we calculated the actual, rather than the prognosticated, cost for each patient. The cost of the Da Vinci system has been calculated based on a 7-year depreciation and 350 procedures per year, the number of procedures actually performed in the system at Sahlgrenska University Hospital each year, using the 2013 calculations of Reynisson and Persson 20 converted to our conditions. Costs have been calculated in US dollars at the Swedish National Bank currency exchange rate of US $1 = 6.51 SEK. The t test was used for statistical calculation to compare costs between groups. RESULTS Demographics A total of 40 patients were included in the robot-assisted laparoscopy group, and a total of 48 were included in the laparotomy group. Regarding demographics, there were no statistical differences in age, BMI, or histological grade between the 2 groups (Table 1). Surgical Outcomes There was a clear significant difference (P G ) between robot-assisted laparoscopy and laparotomy in skin-toskin operative time, favoring robotic surgery, with a mean of 127 minutes (range, 68Y195 minutes) in the robot-assisted laparoscopy group and 179 minutes (range, 97Y306 minutes) in the laparotomy group (Fig. 1). Regarding EBL, there was a statistically significant difference (P G ) between the groups, with a mean of 76 ml (range, 10Y200 ml) in the robotassisted laparoscopy group and 317 ml (range, 50Y1100 ml) in the laparotomy group. There were no differences between the groups in terms of retrieved lymph nodes, with a median of 12 retrieved lymph nodes in both groups and a mean of 13 lymph nodes in both groups with a range of 2 to 35 in the robot-assisted laparoscopygroupand5to29inthelaparotomygroup(table1). There were no conversions to laparotomy in the robotassisted laparoscopy group. Patients undergoing robot-assisted laparoscopy had a significantly shorter hospital stay (P G ), with a mean of 1.8 days, compared with the laparotomy group, with a mean of 4.8 days. Patient Satisfaction Concerning Length Hospital Stay and Recovery Time Patient satisfaction with the duration of the hospital stay was equal in the 2 groups, 97% in the robot-assisted laparoscopy group and 95% in the laparotomy group; this difference was not statistically significant (Table 1). In the robot-assisted laparoscopy group, there was a mean of 5 days to return to preoperative ADL, compared with 14 days in the laparotomy group. This difference was statistically significant (P G ). * 2015 IGCS and ESGO

4 International Journal of Gynecological Cancer & Volume 25, Number 2, February 2015 Robotic Versus Open-Surgery TABLE 1. Demographics and surgical outcome Robot-Assisted Laparoscopy, Mean (Range) Laparotomy, Mean (Range) Statistics Number Age, t test, y 66 (47Y87) 66 (44Y84) NS BMI, Mann-Whitney U test 29 (19Y46) 29 (19Y44) NS Histology grade, W 2 test G1 25% G1 29% G2 53% G2 52% G3 22% G3 19% NS Skin-to-skin operative time, t test, min 127 (68Y195) 179 (97Y306) P G EBL, t test, ml 76 (10Y200) 317 (50Y1100) P G Lymph nodes retrieved, Mann-Whitney U test 13 (2Y35) 13 (5Y29) NS Conversions n = 0 N/A N/A Length of hospital stay, Mann-Whitney U test, d 1.8 (1Y5) 4.8 (2Y11) P G Satisfied with time spent in hospital, W 2 test 97% 95% NS Days to return to normal daily activity, Mann-Whitney U test 5 (1Y28) 14 (4Y42) P G NS, nonsignificant; N/A, not applicable. Complications Complications are stated in Table 2. All intraoperative complications were detected and managed during surgery. One patient in the robot-assisted laparoscopy group had a deep hemorrhage on postoperative day 1, which required second surgery. This patient had a coagulation deficiency and a history of bleeding after previous surgery. Another patient in the robotassisted laparoscopy group had a bladder injury preoperatively, which was repaired during surgery. This patient had a urinary tract infection 10 days postoperatively and had treatment with antibiotics. One month after surgery, the patient developed a vesicovaginal fistula. She was readmitted for corrective surgery, which was successfully performed 3 months postoperatively. None of the postoperative complications generated long-term or permanent symptoms or sequelae in either of the groups. There were no statistically significant differences in intraoperative or postoperative complications. FIGURE 1. Skin-to-skin operative time in minutes for consecutive patients undergoing robot-assisted laparoscopy versus laparotomy. Cost Calculations Costs, calculated according to the case-costing system, were lower in the robot-assisted laparoscopy group, but the difference between the groups was not statistically significant (Table 3). Costs differed between the hospitals, both regarding operating cost per minute and hospital stay per day. The costs for using the operating facilities at the Sahlgrenska University Hospital were the highest, at US $41.5 per minute, compared with a mean of the 3 regional hospitals, at US $39.4 per minute. Costs for 1 hospital day were US $1090 at the Sahlgrenska University Hospital and US $870 as a mean of the regional hospitals. Costs varied between patients and are presented as the mean within the cohort, rather than individually. Calculated robot-associated costs, such as instruments (US $1290), draping (US $246), disposable ports (US $107), and lymph node retrieval bag (US $58), reached a total of US $1701. For robot investment and maintenance costs, we used the costspreviouslycalculatedbyreynissonandpersson 20 converted to our conditions, resulting in a calculated cost of US $958 for investment and US $402 for maintenance, with a total of US $1360 for each procedure. The cost of the Da Vinci system and the additional robot-associated costs yield a total extra cost of US $3061, which was added. No additional costs were added for the laparotomy group. The mean total cost of robot-assisted laparoscopy was calculated at US $15,347, compared with US $15,538 for laparotomy; this difference was not statistically significant (Table 3). DISCUSSION This study presents a prospective, observational study of women with endometrial cancer, focusing on a comparison of robot-assisted laparoscopy and laparotomy. Regarding patient * 2015 IGCS and ESGO 253

5 Eklind et al International Journal of Gynecological Cancer & Volume 25, Number 2, February 2015 TABLE 2. Complications recorded in individual patients undergoing robot-assisted laparoscopy versus laparotomy, respectively Robot-Assisted Laparoscopy Laparotomy Intraoperative complication 2 bladder injury 1 bladder injury 1 serosa injury Early postoperative complication during the hospital stay 1 port hematoma 1 blood transfusion 1 postoperative infectionx NOS 1 dura punction 1 deep bleeding 1 atrial fibrillation Late postoperative complication after discharge 1 vaginal cuff infection 2 wound infections 1 postoperative infection NOS 1 urinary tract infection Late postoperative complication with readmission 1 vaginal cuff infection 1 vaginal cuff infection 1 postoperative infection NOS 1 postoperative infection NOS 1 vesicovaginal fistula 1 subileus NOS, not otherwise specified. safety and satisfaction with the length of the hospital stay, there were no differences between these 2 surgical techniques. Operative time was shorter, recovery time to normal ADL was much shorter, and EBL was lower in the robot-assisted laparoscopy group. We also found that the costs for robot-assisted laparoscopy were not increased compared with laparotomy. Robot-assisted laparoscopy has rapidly become an established method on the surgical arena because it enables the surgeon to apply a minimally invasive method to procedures, for instance lymph node dissections. With the exception of experienced laparoscopic centers, patients undergoing lymph node dissection have traditionally had open surgery performed because traditional laparoscopy has been considered to be difficult or too time consuming. The incidence of endometrial carcinoma is rising, thus increasing the need for surgical procedures, some including lymphadenectomy. Many studies have been conducted on the subject of robotic surgery, but no prospective randomized trials concerning gynecologic oncology procedures have as yet been presented. The possibility to recruit women to randomized trials including lymphadenectomy is slight because most women prefer minimally invasive surgery if asked, and many surgeons are not comfortable with conventional laparoscopy for this procedure, leaving robot-assisted laparoscopy or laparotomy as the remaining options. Several studies, including this one, have shown how robot-assisted laparoscopy benefits the patient, for instance with less blood loss and shorter hospital stay and with no elevated risk of complications. 21Y24 Most of the available studies compare the results of robot-assisted laparoscopy to historical laparotomy material. Our study is, however, a prospective observational study, and the surgeries were performed by experienced, and relatively few, gynecologic oncologists in both groups. The weaknesses of the study are that it is not randomized and that 1 single surgeon did not perform all procedures. Regarding patient satisfaction, it could also be argued that follow-up interviews should have been made continuously during recovery. However, due to the time-consuming task of telephone interviews, this was the decision for our study. Two important outcomes of this study concerns patient satisfaction concerning the length of the hospital stay and recovery. The women participating were telephone interviewed by one in the study participating doctor. Due to practical reasons, we were unable to conduct the interviews at the same time for each patient after surgery. A validated quality of life questionnaire would have been preferred, and future studies may consider using validated questionnaires developed to assess quality of life of cancer patients such as the EORTC QLQ-C30 and evaluate TABLE 3. The mean total cost for 1 patient undergoing robot-assisted laparoscopy and laparotomy, respectively Robot-Assisted Laparoscopy Laparotomy Statistics Surgery and hospital stay US $12,286 US $15,538 Instruments US $1290 Drapings US $246 Disposable ports US $107 Lymph node retrieval bag US $58 Investment cost and maintenance US $1360 Total cost, t test US $15,347 US $15,538 NS NS, nonsignificant. 254 * 2015 IGCS and ESGO

6 International Journal of Gynecological Cancer & Volume 25, Number 2, February 2015 Robotic Versus Open-Surgery different treatment modalities. We found that a vast majority of the participants were very satisfied with the hospital stay and medical care, regardless of surgical method. This study confirms the shorter hospital stay for women in the robot-assisted laparoscopy group previously presented in several other studies, and the incidence of readmission did not differ between the 2groups. 20,25 This study also ascertains that women in the laparotomy group had a 9-day longer convalescence before returning to preoperative ADL. Elderly women are believed to be extra vulnerable in connection with surgery, compared with young women, and benefit from minimally invasive surgery with a short hospital stay and relatively short period of convalescence at home. Shorter hospital stays also enable higher surgical turnover, with more women treated in a shorter period. There is an ongoing discussion about the cost-benefit and effectiveness of health care. The purchase of a robotic system is currently a major investment. New medical equipment is always expensive but can yield value for expenditure if it increases effectiveness or generates better outcome. Until now, most women treated for endometrial cancer including lymphadenectomy underwent open surgery, with the exception of those attending laparoscopic centers where minimally invasive surgery is an option. It has been shown in other studies that the incidence of traditional surgical methods such as both laparotomy and laparoscopy has decreased gradually after the implementation of robot-assisted laparoscopy, implying that the laparoscopic procedure is easier and more feasible for more surgeons with robotic technique, ultimately benefitting the patient. 14,26 The implementation of new methods is inevitable. Robotic surgical technique is a development of conventional laparoscopy and is currently applied in several specialties. The robotic system should be used optimally, enabling as many patients as possible to benefit from the minimally invasive technology. Increasing use distributes the purchasing cost over more surgical procedures, thus lowering it for each procedure. We have chosen to calculate the costs based on our case-costing system with the actual cost per minute for the operating room and ward care per day, including extra laboratory costs and radiology costs if required. For the robot-assisted laparoscopy group, we have also included the costs of the instruments and draping for each procedure as well as the costs of investment for and maintenance of the Da Vinci system. We chose not to include any extra costs for investment or single-use instruments in the laparotomy group to simplify cost calculations, but this might be reconsidered in future studies in an attempt to make accurate cost calculations for laparotomy as well. Furthermore, our case-cost system could facilitate further analyze and calculate costs, for example, within a year from primary surgery, to get a complete cost analysis, but it would demand a thorough and difficult investigation to separate costs for adjuvant radiotherapy and chemotherapy and its adverse effects and the patients comorbidity. Although the costs for operating time and hospital care were higher at the university hospital than at the regional hospitals, and all extra costs in the robot-assisted laparoscopy group were taken into consideration, robot-assisted laparoscopy was still performed without increased costs compared with laparotomy. This is an essential finding in our study. Previous studies have indicated that robot-assisted laparoscopy is more time consuming, compared with laparotomy, which was not the case in this study. 9,14,21,27 On the contrary, we found that with experienced surgeons in both groups, robotassisted laparoscopy required significantly shorter operative time than laparotomy, almost 1 hour less. This is probably due to the robotic technique that enables the surgeon to use the camera, bipolar and unipolar diathermia, and instruments simultaneously and without giving orders to an assistant. Given shorter operative time and hospital stay with robot-assisted laparoscopy, the cost is not higher than that for laparotomy. Our results show no statistically significant difference between the groups implicating that robot-assisted laparoscopy is cost-effective, and most importantly, patients underwent minimally invasive surgery and had a shorter recovery time. CONCLUSIONS This study shows that robot-assisted laparoscopy for women with endometrial carcinoma undergoing hysterectomy, BSOE, and pelvic lymphadenectomy is associated with significantly shorter operative time and hospital stay as well as lower EBL and quicker recovery to normal ADL, without an increased total cost compared with laparotomy. Robot-assisted laparoscopy is a feasible and cost-effective surgical technique in women with endometrial carcinoma compared with laparotomy. ACKNOWLEDGMENTS The authors would like to thank their colleagues at the Department of Obstetrics and Gynecology at SödraÄlvsborg Hospital in Borås, Sweden, Norra Älvsborg Hospital in Trollhättan, Sweden, and at Skaraborg Hospital in Skövde, Sweden for being instrumental in the conduction of this study and for cooperating by sharing their data. Particular thanks to Dr Mårten Torle, Dr Eva Blank, and Dr Maria Widmark. The authors are also grateful to Erik Bulow for the statistical assistance. REFERENCES 1. 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