Sentinel lymph node detection in endometrial cancer with indocyanine green: laparoscopic versus robotic approach

Background: The aims of the present study were to assess bilateral sentinel lymph node (SLN) mapping with laparoscopic versus robotic approach, to assess variables affecting bilateral detection rates and to assess survival difference in patients with no/unilateral, compared to bilateral SLN detection. Methods: This is a retrospective, single-centre, observational cohort study, including patients with endometrial cancer FIGO stage IA-IVB, treated with minimally invasive primary surgery and undergoing indocyanine green (ICG) injection to detect SLN, between January 2015 and December 2019. Results: Of the 549 included patients, 286 (52.1%) and 263 (47.9%) underwent the laparoscopic and robotic approach respectively. 387 (70.5%) patients had bilateral SLN mapping, 102 (18.6%) and 60 (10.9%) had unilateral and no mapping, respectively. Patients who underwent the robotic approach were older (median 61 versus 64 years, p=0.046) and had a higher BMI (median 26.0 versus 34.8 kg/m2, p<0.001). No difference in any SLN mapping or in SLN bilateral detection was evident between the laparoscopic or robotic approach (p=0.892 and p=0.507 respectively). Patients with bilateral SLN detection in the entire cohort were younger (p<0.001) and had a better 3-year disease-free survival (DFS) compared to patients with no/unilateral SLN mapping (77.0% versus 66.3%, respectively, p=0.036). No 3-year overall survival (OS) difference was reported (p=0.491). Conclusion: SLN mapping and bilateral SLN detection with ICG in endometrial cancer was not different in the laparoscopic and robotic approach, even though patients undergoing the robotic approach were older and more obese. Bilateral SLN detection was associated with improved 3-year DFS, but not with 3-year OS, compared to no and unilateral SLN detection.


Introduction
Endometrial cancer is the most frequent gynaecological cancer in developed countries, with 65,620 estimated new cases and 12,590 estimated deaths in 2020 in the United States (Siegel et al., 2020).
Sentinel lymph node (SLN) mapping is now widely utilised in the staging process for apparent uterineconfined endometrial cancer and this is supported by large literature evidence (Koh et al., 2018;Bodurtha Smith et al., 2017;Rossi et al., 2017). The goal of this strategy is to remove the first tumour draining lymph nodes and to evaluate them by ultra-staging in order to obtain an accurate diagnosis of nodal status with limited surgical morbidity, especially lymphoedema (Geppert et al., 2018). Near-infrared technology and the use of indocyanine green (ICG) recently emerged as the dye of choice for SLN, as it allows a higher bilateral mapping, which is a crucial factor in SLN technique (Papadia et al., 2017;Frumovitz et al., 2018;Rozenholc et al., 2019). Different studies on SLN in endometrial cancer analysed the efficacy of the laparoscopic (Geppert et al., 2018;Papadia et al., 2017;Papadia et al., 2016) and robotic approach (Casarin et al., 2020;Stephens et al., 2020) in SLN mapping. Robotic surgery has been demonstrated to show perioperative advantages, especially in morbidly obese endometrial cancer patients, with a significant reduction in conversion rate to laparotomy (Leitao et al., 2016;Corrado et al., 2018). Nevertheless, the increase of body mass index (BMI) has been associated with decreased rate of bilateral SLN detection (Eriksson et al., 2016;Tanner et al., 2015), particularly when blue dye, rather than ICG, is used as a tracer (Sinno et al., 2014). More recently, a significant advantage in terms of overall and bilateral SLN mapping in obese patients with ICG compared with blue dye, was reported (Eriksson et al., 2016).
To the best of our knowledge, there is only one study which specifically compared the robotic versus the laparoscopic approach with regards to SLN detection rate with ICG (Chaowawanit et al., 2020), but this was limited by the low number of patients. The primary aim of this present study was to assess whether there is a difference in bilateral detection rate of SLN in endometrial cancer treated with the laparoscopic versus the robotic approach; secondary aims were to assess variables affecting bilateral detection rates in the entire cohort and to assess survival difference in patients with no and unilateral, compared to bilateral SLN detection.

Materials and Methods
This is a retrospective, single-centre, observational cohort study, approved by the Institutional Review Board (number DIPUSVSP-26-05-2064). Clinical and pathological data was retrieved from the RedCap ® institutional electronic database. All patients with a histological diagnosis of endometrial cancer, International Federation of Gynecology and Obstetrics -FIGO stage (Pecorelli et al., 2009) IA-IVB, treated with primary surgery between January 2015 and December 2019 at Fondazione Policlinico Agostino Gemelli IRCCS, Rome, Italy, were included.
Only patients who received ICG injection to detect SLN and underwent total hysterectomy and bilateral salpingo-oophorectomy were included. Patients who underwent fertility sparing procedures, neo-adjuvant treatment, in whom hysterectomy was not performed, who had no SLN mapping attempted, or with leiomyosarcoma and endometrial stromal sarcoma histology, were excluded. All patients underwent in a pre-operative pelvic ultrasound scan (US) and a computed tomography (CT) scan of chest-abdomen-pelvis (to exclude distant metastases). Only patients submitted to the minimally invasive surgical approach were included: decision to operate on patients utilising the laparoscopic or robotic approach depended on the patient's BMI and robotic platform availability. In general, patients with a BMI > 30 kg/m2 were selected for the robotic approach. Only patients with no evidence of enlarged (short axis >10mm) pelvic or para-aortic lymph nodes were submitted to SLN mapping. SLN was detected after 1 ml superficial and deep cervical injections of ICG (diluted with sterile water at 1.25 mg/ml) at 3 and 9 o'clock. ICG injection was performed after docking in the case of robotic surgery. About 10-15 minutes after the cervical injection, the retroperitoneal space was opened, and pelvic lymph nodes were assessed with a near infra-red (NIR) camera (Olympus, Tokyo, Japan in case of laparoscopic or Da Vinci Xi, Intuitive, Sunnyvale, California, US in case of robotic approach). SLN was defined as the ICG-positive lymph node closest to the uterus. Pelvic retroperitoneal spaces were explored with the following order to assess SLN mapping: external iliac, inter-iliac, obturator, common iliac, parametrial and pre-sacral and low para-aortic area.
If no pelvic SLN was detected, the para-aortic area was explored trans-peritoneally and the retroperitoneal para-aortic area was accessed in cases of ICG-positive para-aortic SLN. In cases of apparent early-stage tumours (FIGO stage I-II), if bilateral pelvic SLNs were detected, these were sent to pathology for analysis with ultra-staging or one-step nucleic acid amplification (OSNA) (Fanfani et al., 2018;Monterossi et al., 2019). In case of ultrastaging analysis no further lymph node dissection was performed (Koh et al., 2018), and nodes were sent for final histology. In case of OSNA analysis, the SLN was reported intra-operatively and lymphadenectomy was performed in patients with positive SLNs (for micro-metastasis or macro-metastasis). When SLN was not identified, deep cervical ICG re-injection was performed. In cases with no mapping on a hemi-pelvis, a sidespecific pelvic lymphadenectomy was performed (Koh et al., 2018). Moreover, in the first patients of our series, SLN was performed along with pelvic lymphadenectomy as institutional validation of the SLN technique, even in low and intermediate risk patients. Patients with serous histology underwent additional peritoneal staging including infracolic omentectomy and multiple peritoneal biopsies (Koh et al., 2018;Colombo et al., 2016). Adjuvant treatment was administered according to international guidelines (Koh et al., 2018).

Statistical analysis
Standard descriptive statistics were used to evaluate the distribution of each variable. Continuous variables were reported as median and categorical variables as frequencies or percentages. The distribution of variables between groups was compared with student's t-test, chi-square test or Fisher's exact test, as appropriate. Logistic regression analysis was performed to perform univariate and multivariable analyses. Intraoperative complications were graded according to Common Terminology Criteria for Adverse Events (CTCAE) v. 5.0, and post-operative complications were graded according to Clavien-Dindo grading system (Dindo et al., 2004). Disease-free survival (DFS) was defined as the time in months from the date of the surgery to the date of first recurrence, last follow-up or death. Overall survival (OS) was calculated as the time in months from the date of the surgery to the date of the last follow-up or death. OS and DFS were estimated by the Kaplan-Meier method (Kaplan and Meier 1958) and compared by the log-rank test (Mantel 1966). All p-values reported are two-sided and a p-value <0.05 was considered statistically significant. All statistical analyses were performed with SPSS version 26.0 (IBM Corporation 2018, Armonk, NY: IBM Corp.).

Entire cohort characteristics
Out of 869 patients who underwent surgery for endometrial cancer in the study period, 549 (63.2%) met the inclusion criteria.
Survival analysis of the entire cohort showed, with a median follow-up of 11 months (range, 0-57), that 30 (5.5%) patients had a recurrence and 8 (1.4%) died of the disease.
No 3-year DFS and OS difference was evident when patients undergoing SLN only were compared to patients undergoing SLN and systematic lymphadenectomy (p=0.402 and p=0.267).

Comparison of laparoscopic and robotic approach
Comparison of characteristics of the laparoscopic (286, 52.1%) and the robotic approach (263, 47.9%) are reported in Table II. Patients who underwent the robotic approach were older (median 61 versus 64 years, p=0.046) and had, as expected, a higher BMI (median 26.0 versus 34.8 kg/m2, p<0.001). No difference in conversion to laparotomy was detected (2.8% versus 0.8%, p=0.109). No difference in any SLN mapping or in SLN bilateral detection was evident between the laparoscopic or robotic approach (p=0.892 and p=0.507, respectively). Moreover, there was no difference in median number of SLNs mapped and retrieved between the two approaches (2 in both groups, p=0.650) and in site of SLN mapping (p=0.057). Figure 1A and Figure 1B shows two examples of SLN mapping in laparoscopic and robotic surgery, respectively.

Comparison of no/unilateral and bilateral SLN detection
Analysis of variables associated with bilateral SLN detection, compared with no/unilateral SLN detection within the entire cohort, are reported in Table III. Age was the only patient-related characteristic which was associated with bilateral SLN detection: patients with bilateral SLN detection were younger than patients with no/  However, no bilateral SLN detection difference was evident when the two learning periods were stratified according to the surgical approach, laparoscopy versus robotic (p=0.758 and p=0.427, for the first and second period, respectively). Age < 65 years and an experienced period of surgery were the only variables related to bilateral SLN detection at multivariable analysis (Table IV). There was no difference in intra-operative complication rate between patients who had bilateral and patients who did not have bilateral SLN mapping. Post-operative complications were more frequent in patients who did not have bilateral mapping (6.2% versus 1.8%, p=0.012). However, no difference in severe post-operative complications was recorded (p=0.682). Lastly, patients with bilateral SLN detection were found to have higher numbers of SLN metastases: in particular they had a higher rate of isolated tumour cells (ITCs) and micro-metastases (p=0.022).
Survival comparison demonstrated that patients with bilateral SLN mapping had a better 3-year DFS compared to patients with no/unilateral SLN  (Figure 2A). No difference in 3-year OS between the two groups was reported (90.9% versus 89.2%, p=0.491) ( Figure 2B).

Discussion
With the present study, we demonstrated that endometrial cancer patients operated using the robotic or laparoscopic approach had no difference in SLN mapping and bilateral detection rate, despite the signifi cantly higher BMI of patients submitted to robotic surgery. This is in contrast with previous studies, which correlated the higher BMI with no or unilateral SLN mapping (Eriksson et al., 2016;Tanner et al., 2015). Moreover, this is in contrast with a very recent study that found a higher overall detection rate using the laparoscopic approach, compared to robotic (with no difference in bilateral detection rate) (Chaowawanit et al., 2020). Nevertheless, other studies reported that BMI was As previously reported (Bogani et al., 2019), a higher rate of low-volume metastases (ITC and micrometastasis) was observed in patients with successful bilateral SLN mapping. We could assume that this is a consequence of the more accurate analysis of the SLN, rather than single section analysis of multiple lymph nodes in lymphadenectomy specimens by standard hematoxylin and eosin (H&E).
At survival analysis, a signifi cant better 3-year DFS in the group of patients with bilateral SLN detection compared to those with no/unilateral SLN detection was observed (p=0.033). On the contrary, no signifi cant differences in terms of OS between the two groups was observed. Therefore, SLN can be interpreted as a more accurate tool to detect positive lymph nodes, with consequent tailored adjuvant treatment. Nevertheless, the lack of OS impact could indicate that patients with recurrent disease can be successfully treated at relapse (Connor et al., 2018;Legge et al., 2020).
We have to acknowledge the retrospective nature, a possible selection bias to the surgical approach and the short median follow up, as main limitations of the present study. On the other hand, we have to recognise the large number of patients submitted to ICG SLN from a single institution and the fact that this is one of the fi rst studies comparing performance of the laparoscopic and robotic approach in SLN mapping.

Conclusion
SLN mapping and bilateral detection rates in endometrial cancer were no different between the laparoscopic or robotic approach, even though patients undergoing the robotic approach were older and more obese. Younger age affected the bilateral SLN detection rate in the entire cohort. Bilateral SLN detection was associated with improved 3-year DFS, but not with 3-year OS, compared to patients with no and unilateral SLN detection. not a clinical characteristic which infl uenced the rate of bilateral SLN detection (Stephens et al., 2020;Tortorella et al., 2019;Body et al., 2018). Furthermore, our results further support the use of robotic surgery in obese and morbidly obese women, as previously reported by other authors (Leitao et al., 2016;Corrado et al., 2018).
The relevance of bilateral SLN detection is explained by the fact that SLN can be analysed with thorough examination, avoiding systematic lymphadenectomy related morbidity (Geppert et al., 2018). When we analysed the factors that potentially infl uence bilateral SLN detection in the entire cohort, we found that age was the only patient-related signifi cant variable, confi rmed at multivariable analysis. Most of the studies previously reported other variables signifi cantly related with bilateral SLN mapping, such as use of ICG, low BMI, no clinically enlarged lymph nodes, early FIGO stage, no lysis of adhesions at the beginning of surgery and surgeon's experience in SLN biopsy (Eriksson et al., 2016;Tanner et al., 2015;Tortorella et al., 2019;Body et al., 2018;Harold et al., 2019;Sozzi et al., 2020). The relationship between increased age and lymphatic dysfunction has been described: in particular, cell senescence, impaired contractile function and decrease of nitric oxide in aged lymphatic collectors, may lead to poor drainage of lymph, causing bilateral mapping failure (Shang et al., 2019).
In our study, we confi rmed that the learning curve of ICG injection and SLN mapping, signifi cantly affected the rate of bilateral SLN detection, by observing a significantly higher bilateral SLN detection in the second period of our series. As expected, patients with no/unilateral SLN detection had signifi cantly higher post-operative complications, most probably due to uni-or bilateral pelvic lymphadenectomy performed. Nevertheless, no difference in severe post-operative complications was found between patients with or without bilateral SLN detection.