Functional and Oncologic Outcomes Following Perinatal Tissue Allograft Placement During Nerve-Sparing Robotic-Assisted Radical Prostatectomy

Erectile dysfunction (ED) following robotic-assisted radical prostatectomy (RARP) is attributed to iatrogenic nerve injury to the cavernous nerve bundles¹. These nerves course posterolaterally along the prostate and are highly susceptible to mechanical, thermal, and ischemic injury during dissection^2,3,4. Rates of ED at 1 year following RARP vary but are estimated to be as high as 46%⁵. Similarly, urinary incontinence following RARP is primarily due to sphincteric dysfunction caused by the removal of the internal urethral sphincter and concomitant injury to the nerves of the external sphincter⁶. Depending on the definition of continence, studies find rates of urinary continence 1 year following RARP are between 40% and 95%^5,7. Given the high prevalence of ED and urinary incontinence, numerous studies have consistently demonstrated that treatment with prostatectomy has a significant impact on a patient's quality of life^8,9,10

To improve urinary continence and erectile function following RARP, various surgical techniques have been developed. Among the most impactful of these techniques is sparing of the prostatic neurovascular bundles. Periprostatic nerve fibers are visually preserved intraoperatively with the intended result of improved functional outcomes over time. However, even when utilizing the nerve-sparing approach, continence and erectile function can take up to 1 year to return following RARP¹¹. One proposed strategy to enhance recovery of the preserved periprostatic neurovascular tissue is through intraoperative placement of perinatal tissue allografts. Preclinical studies have shown that perinatal tissue allografts can serve as a cover (i.e., wrap) to protect the cavernous nerves from the local microenvironment^12,13,14,15. Although current clinical evidence remains limited, findings suggest that the use of perinatal tissue allografts during RARP may accelerate the return of urinary continence and potency^{16,17,18,19,20,21,22,23}. With this study, we aim to bridge the gap between promising preclinical results with tissue allografts by examining intraoperative feasibility and safety with a single surgeon series. The tissue allograft utilized in this study is a dehydrated, full-thickness perinatal tissue allograft containing the amnion, intermediate, and chorion layers. It is considered a 361HCT/P by the US FDA. It has been processed with its contiguous layers remaining intact (i.e., non-separated) to retain all original relevant characteristics of the tissue. It exhibits excellent handling characteristics and thus may be beneficial for use in robotic surgeries as a covering and protective barrier. This case series includes a detailed intraoperative description of the allograft preparation and placement with supporting data demonstrating intraoperative safety and postoperative rates of biochemical recurrence. To our knowledge, this is the first reported case series utilizing the multi-layer graft (MLG-Complete) from Samaritan Biologics. We aim to add to the growing body of literature supporting the safety of perinatal tissue allografts in the setting of prostate cancer. The primary objective of this case series is to evaluate the feasibility and safety of placing perinatal tissue allografts in patients undergoing nerve-sparing RARP by examining intraoperative complication rates and rates of biochemical recurrence. The secondary objective is to determine the impact of intraoperative placement of the perinatal tissue allografts on postoperative erectile function and urinary continence in RARP patients.

Institutional review board approval was granted by Mayo Clinic (IRB Application 23-013215) for this case series. Informed consent was obtained for all participants. All data used in this study were de-identified prior to analysis.

Study overview
The study aims to evaluate the feasibility, safety, erectile function, and urinary continence recovery in patients with localized prostate cancer following treatment with nerve-sparing RARP with adjunct placement of a perinatal tissue allograft (Table of Materials). All data recorded for this study were collected and transcribed into a secure REDCap (Research Electronic Data Capture) database. Continuous variables were reported as a median and interquartile range. Categorical variables were reported as absolute and percentage frequencies. The study overview can be visualized in Figure 1.

Preoperative screening
Subjects for this study were identified as having biopsy-proven localized prostate cancer who underwent bilateral or unilateral nerve-sparing RARP and placement of the perinatal tissue allograft around their cavernous nerve(s) at Mayo Clinic Jacksonville between 2022 and 2024. Subjects were selected at the discretion of the primary investigator (RP) based on the following inclusion and exclusion criteria. Male subjects had to be at least 45 years of age and had a primary diagnosis of organ-confined (i.e., localized), untreated prostate cancer who elected for surgical intervention in the form of unilateral or bilateral nerve-sparing RARP. Pre-operatively, the patients had to be sexually potent as indicated by a sexual health inventory score for men (SHIM) of equal to or greater than 19. Subjects were excluded if they had neoadjuvant therapy planned for high-risk cancer, full excision of neurovascular bundles, or were unable to comply with learning and documenting penile rehabilitation (oral 5-phosphodiesterase inhibitor (PDE-5i) use, vacuum pump therapy use, and/or injectable medications). Subjects with a history of more than 2 weeks of treatment with immunosuppressants (including systemic corticosteroids), cytotoxic chemotherapy within 1 month of surgery, or who were anticipated to require such medications during the course of the study were excluded. Additionally, subjects that had prior hormonal therapy, such as Lupron or oral anti-androgens, were excluded. Subjects with poor urinary control prior to surgery requiring the use of pads for leakage, a previous history of pelvic radiation, simple prostatectomy or transurethral prostate surgery, and those who were considered obese (BMI > 40 kg/m²) were excluded. Additional exclusions included patients with the following: a history of open pelvic surgery within 5 years of RARP (except for hernia repair), plans to undergo chemotherapy, radiation, hormone therapy, or open surgery, any neurologic disorder or psychiatric disorder that might confound postsurgical assessments, a known history of poor adherence with medical treatment, a history of drug or alcohol abuse within the 12 months prior to surgery, received administration of an investigational drug within 30 days prior to surgery, or administration of another investigational product during surgery or the follow-up period.

Allograft donation
Membranes were recovered from qualified donors and processed under aseptic conditions in accordance with federal, state, and/or international regulations and to the standards of the American Association of Tissue Banks. Each donor was screened and tested for communicable disease risks and other exclusionary medical conditions. The results of the donor screening and testing were reviewed by a Medical Director (or licensed physician designee), and the donors were deemed eligible for transplantation. Communicable disease testing was performed by an FDA-registered laboratory certified to perform such testing on human specimens under the Clinical Laboratory Improvement Amendments of 1988 (42 U.S.C. 263a) and 42 CFR part 493, or that has met equivalent requirements as determined by the Centers for Medicare and Medicaid Services in accordance with those provisions. All efforts were made to ensure the safety of the allograft, but there was no assurance that the allograft was entirely free from all infectious diseases or microbial contamination.

Allograft preparation
MLG-COMPLETE allografts from Samaritan Biologics were prepared at dimensions of 3 cm x 6 cm and a thickness of approximately 0.15-0.20 mm and were terminally sterilized by irradiation to a sterility assurance level of 1 x 10^-6.²⁴ Perinatal tissue allografts were stored at room temperature. At the time of implantation, allografts were handled using aseptic technique: the outer peel pouch was inspected and opened to present the inner foil pouch to the operative field. The inner pouch was only opened when it was time for allograft placement. Allografts were then completely submerged in 100 mL of room temperature sterile normal saline (0.9% weight/volume) for 10 s. This pre-hydration technique was utilized to make the graft more malleable for passage through the robotic ports, although this step was not required for successful placement. Handling instructions of the allograft following hydration are described in Figure 2.

Allograft application
Transperitoneal nerve-sparing RARP was performed utilizing a Da Vinci Xi surgical robot. A pneumoperitoneum of 15 mmHg was maintained throughout the operation. The robotic camera provided 10x magnification. A digital zoom option was available but was not utilized during the operation. An anterior approach with hood technique was performed when possible²⁵. Nerve-sparing technique was selected at the surgeon's discretion, with the goal of minimal use of monopolar cautery for maximal nerve preservation. After prostatic apex dissection, a 3 cm x 6 cm pre-hydrated perinatal tissue allograft was oriented longitudinally and introduced through the 8 mm assistant port using an atraumatic laparoscopic grasper. The surgeon then positioned the graft laterally and placed it on the preserved neurovascular bundle. Graft placement was guided by direct visual cues (Figure 3). Coverage was considered successful when the graft enveloped at least 90% of the visible bundle circumference without evidence of displacement, as demonstrated in Video 1. Placement of the allografts was completed in under 5 min to avoid prolonging the operative time. The urethrovesical anastomosis was completed with a double-armed 3-O V-Lok with a posterior Rocco stitch. One high-volume RARP surgeon (RP) performed all 14 cases. Following RARP, subjects were discharged from the hospital on postoperative day 0 (primarily) or postoperative day 1. The majority of patients underwent same-day discharge to a virtual hybrid care model²⁶. They returned to the clinic 7-10 days later for catheter removal and were asked to take either sulfamethoxazole-trimethoprim 400-80 mg or cefdinir 300 mg in the morning and evening on the day of catheter removal, per routine practice.

Oncological staging and pathological assessment
The American Joint Committee on Cancer (AJCC) TNM classification system was utilized to classify oncologic outcomes²⁷. Clinical (T) stage was determined by pre-operative digital rectal exam, while clinical node (N) stage was based on available pre-operative imaging. Final grade group and pathological staging were assigned based on histopathological evaluation of the prostatectomy specimen analysis by board-certified pathologists. Prostate volume was measured from preoperative MRI, and prostate weight was recorded from the final pathology report.

Postoperative evaluation
The PI conducted follow-up visits with the subjects at 6 weeks, 3 months, 6 months, and 9 months at the Urology Clinic. Sexual potency was defined as achieving a post-operative SHIM of equal to or greater than 17 with or without the use of phosphodiesterase-5 inhibitors (PDE-5i). Urinary continence was defined as the absence of uncontrollable leakage of urine requiring equal to or less than one urinary pad per day postoperatively. Biochemical recurrence of prostate cancer was defined as having a postoperative prostate-specific antigen (PSA) level of greater than 0.2 ng/mL. Intraoperative complications were defined as any adverse event or deviation from the normal operative course, in accordance with standardized surgical outcome reporting guidelines.

Study overview
A total of 14 patients underwent perinatal tissue allograft placement. Demographic and follow-up data were available for all patients 6 months postoperatively. 12 patients were available for follow-up data at 9 months postoperatively. 2 patients chose to follow up with their local urologist.

Study population
Patient demographic data for all patients included in this case series are given in Table 1. The median age (IQR) in years at diagnosis was 63 (58.5-67.0), with a median BMI (IQR) of 28.5 (27.25-31.0). The median preoperative SHIM (IQR) and American Urologic Association Symptom Index (AUA-SI; IQR) were 24 (23.0-25.0) and 6.0 (3.0-12.5), respectively. The median operative time (IQR) in min was 216.0 (206.0-234.8), with a median blood loss (IQR) in mL of 100 (43.8-222.5). Patients maintained a catheter postoperatively for a median day (IQR) of 7.0 (7.0-8.5). Four (28.6%) of our patients were previously diagnosed with ED, and 10 (71.4%) were previously diagnosed with benign prostatic hyperplasia (BPH). All patients were sexually active prior to surgery. 13 (92.9%) of these patients were treated with bilateral nerve sparing, while 1 (7.1%) patient was treated with unilateral nerve sparing. No intraoperative complications occurred.

Oncological outcomes
Postoperative oncological outcomes following nerve-sparing RARP with perinatal tissue allograft placement were available for all, but 1 patient included in this study (Table 2). Postoperative analysis of the prostatic specimen revealed that 6 of 14 (42.9%) patients had histological findings consistent with ISUP Grade Group 2 prostate cancer. 11 of 14 (84.6%) patients presented with a T1c clinical tumor stage, while 12 of 14 (85.7%) patients were found to have T2 pathological tumor stage. 13 patients had N0 clinical node stage and N0 pathological node stage with pathological nodal data (Nx) unavailable for 1 patient. Median prostate volume (IQR) in mL on MRI was 39.0 (33.0-56.0), and median prostate weight (post-RARP) in g (IQR) was 46.5 (38.0-62.8). No patients experienced biochemical recurrence at any point during follow-up (PSA > 0.2 ng/mL).

Functional outcomes
Potency
At 6 weeks, 3 months, 6 months, and 9 months postoperatively, 4 of 7 (51.7%), 11 of 14 (78.6%), 12 of 14 (85.7%), and 11 of 12 (91.7%) patients, respectively, were able to achieve erections (Table 3, Figure 4). 8 of 14 (57.1%) patients achieved potency in a median day (IQR) of 90 (42.0-157.5). By 6 weeks postoperatively, 3 of 14 (21.4%) patients achieved potency. By 3 months postoperatively, 6 of 14 (42.9%) patients achieved potency, with 2 of these patients achieving SHIM scores ≥ 21. By 6 months postoperatively, 7 of 14 (50.0%) patients achieved potency, and of these, 3 patients achieved SHIM scores ≥ 21. By 9 months postoperatively, 8 of 14 (57.1%) patients achieved potency, and of these 4 patients achieved SHIM scores ≥21. The remaining 6 patients had not attempted sexual intercourse at 9 months postoperatively.

Continence
At 6 weeks, 3 months, 6 months, and 9 months postoperatively, 3 of 5 (60.0%), 8 of 14 (57.1%), 10 of 14 (71.4%), and 9 of 12 (75.0%) patients, respectively, achieved or maintained continence (Table 4, Figure 5). 9 of 12 (75%) patients achieved continence in median days (IQR) of 90 (42.0-112.5). The remaining 2 patients had not achieved continence at 9 months postoperatively. One of these patients required surgical urethral sling placement.

Conclusion

Our findings support the use of perinatal tissue allograft placement as a protective covering during RARP. These findings also suggest that the use of the perinatal tissue allografts facilitates earlier return of potency and continence in a median of 90 days. These results align with previously published studies supporting the role of perinatal tissue allografts in hastening functional recovery16,17,18,19,20,21,22,23. This strategy appears to be safe and technically feasible, with no intraoperative complications observed. Additionally, the data demonstrates promising functional outcomes without evidence of compromised oncologic control. Further research will be conducted to directly compare this subset of patients to the outcomes of patients undergoing nerve-sparing RARP alone.

Data availability:
Study data was managed using REDCap version 15.0.33, a secure web-based platform for research data capture. Data entry and navigation were performed through the Mayo Clinic secure server. The data supporting this study's findings are available from the corresponding author upon reasonable request. Due to institutional policies, the data is not publicly available.

Figure 1: Study overview. Overview of study cohort and surgical parameters for patients undergoing nerve-sparing RARP with intraoperative amniotic membrane allograft placement. Please click here to view a larger version of this figure.

Figure 2: Handling characteristics of the MLG-COMPLETE perinatal tissue allograft. The pre-hydrated graft (black arrow) was (A) conformed to the contours of a gloved finger, (B) rolled up between the fingers, prior to (C) unfurling the graft and (D) recontouring the allograft to the gloved finger. Please click here to view a larger version of this figure.

Figure 3: Intraoperative perinatal tissue allograft placement during nerve-sparing RARP. Coverage of neurovascular bundles with perinatal tissue allograft. Please click here to view a larger version of this figure.

Figure 4: Proportion of patients with erections. Two patients were followed up locally, and therefore, data for them were unavailable. Please click here to view a larger version of this figure.

Figure 5: Proportion of patients with urinary continence. Continence was defined as ≤1 pad per day. Two patients were followed up locally, and therefore, data for them was unavailable. Please click here to view a larger version of this figure.

Table 1: Baseline patient characteristics. Baseline demographic, clinical, and perioperative characteristics of patients undergoing nerve-sparing RARP with amniotic chorionic membrane allograft placement. Data are presented as median (interquartile range) or number (%).

Table 2: Oncological outcomes. Tumor characteristics and prostate metrics of patients undergoing nerve-sparing RARP with amniotic membrane allograft placement. Data are presented as median (interquartile range) or number (%). *Data not available for all patients.

Table 3: Percentage of patients reporting erections postoperatively. *Two patients were followed up locally, and therefore, data for them were unavailable.

Table 4: Percentage of patients reporting continence postoperatively. Continence was defined as ≤1 pad per day. *Two patients were followed up locally, and therefore, data for them were unavailable.

Video 1: Intraoperative nerve-sparing and perinatal tissue allograft placement during RARP. The first clip demonstrates neurovascular bundle dissection, with minimal use of monopolar cautery.The second frame shows the introduction of the perinatal tissue allograft through the assistant port and the placement of the perinatal tissue allografts around each neurovascular bundle. Please click here to download this Video.

This case series provides important information on the technical feasibility, functional, and oncological outcomes associated with the use of perinatal tissue allografts placement during nerve-sparing RARP. The results showed a median return to both potency and continence of 90 days, with 57.1% and 75.0% of patients achieving potency and continence, respectively. Additionally, there was no biochemical recurrence or intraoperative complications, speaking to the safety of perinatal tissue allografts. These findings add to a growing body of evidence suggesting that perinatal allografts have the potential to improve postoperative recovery of neurovascular structures following RARP¹⁵.

The median time to potency of 90 days reported here is comparable to and arguably more favorable than those reported in available clinical literature. In a study conducted by Noel et al., over 500 patients underwent nerve-sparing RARP treated with intraoperative placement of amniotic-chorionic membrane allografts. This study found the median (IQR) time in days to potency for men older than 55 was 167 (42-549). Noel and colleagues defined potency as the ability to achieve and maintain an erection with or without PDE-5 inhibitors¹⁷. Notably, the median postoperative SHIM score in this subgroup was 15 -- lower than our study's threshold SHIM score of 17 for potency -- suggesting our definition was more stringent. Similarly, Patel et al. conducted a comparative study of patients undergoing nerve-sparing RARP with and without dehydrated amniotic-chorionic membrane graft placement. They reported a significantly shorter time to potency in the allograft group (1.34 months) compared to controls (3.39 months). In this study, 65.5% of graft recipients achieved potency versus 51.7% in the control group. Our median time to potency was slightly longer, which may be attributable to the older patient population in this study (median age 63 versus 56 years)¹⁷. Nonetheless, our potency rate was higher than that of their control group, with 57.1% of patients achieving potency. Collectively, these comparisons support the promising role of perinatal tissue allografts in facilitating earlier and more robust return of erectile function following nerve-sparing RARP.

While less pronounced than our potency outcomes, our continence results also align with existing literature. Noel et al. demonstrated a median time to continence of 42 days following allograft placement¹⁷. Notably, this study used a more lenient definition of continence -- absence of uncontrolled leakage -- but still reported that 97.7% of patients were using one or fewer pads per day. As mentioned above, a continence rate of 75.0% is currently limited to a 9-month follow-up and is expected to improve with extended observation.

Since Alvim et al. found faster relapse in prostate tumor cell models treated with perinatal allografts compared to controls, the influence of perinatal allograft placement on biochemical recurrence of prostate cancer is of significant concern²³. Concerns have also been raised regarding whether graft placement may increase the risk of postoperative complications or operative time. Our results are reassuring as we observed no evidence of increased biochemical recurrence rates, intraoperative complications, and had a median operative time of less than 4 h. This supports the safety profile of perinatal tissue allograft use in the context of nerve-sparing RARP.

This case series has several important limitations that should be acknowledged. Most notably, the absence of a control group limits the ability to draw definitive conclusions about the efficacy of perinatal tissue allograft placement. A logical next step will be a comparative analysis using data from nerve-sparing RARP procedures performed by the same surgeon without perinatal allograft placement to more accurately assess relative outcomes. Additionally, all procedures in this study were performed by a single surgeon and were retrospective in nature, introducing the potential for operator-dependent bias, given nuanced variability in nerve-sparing techniques. Future studies could include prospective randomized controlled trials or multicenter studies, which would reduce operator-dependent bias, increase generalizability, and provide more rigorous evidence regarding the efficacy of perinatal tissue allograft placement. We are currently recruiting patients prospectively evaluating the perinatal tissue allograft at the time of prostatectomy (NCT06940271). The follow-up period here was limited to less than 1 year, and longer-term data will be necessary to evaluate the durability of both functional and oncologic outcomes. This study only examined one specific type of perinatal allograft, and future research should explore comparative effectiveness among different graft preparations. Finally, incorporating cost-benefit analyses will help clarify the clinical and economic value of routine allograft use in nerve-sparing RARP.