This study aims to find out which surgical position is safer and works better for patients candidate to robot-assisted partial nephrectomy (RAPN) - a minimally invasive procedure to remove a small kidney tumor while preserving healthy kidney tissue.

During this operation, the patient can be placed in two different positions:

• the standard flank position, where the patient lies on their side
• a newer supine position, where the patient lies on their back using a technique called Supine Anterior Retroperitoneal Approach (SARA).

Both approaches are performed using the Da Vinci® Single Port (SP) robotic system, a state-of-the-art surgical robot that allows the operation to be done through a single small incision.

The traditional flank position has been used for many years, but it can be uncomfortable for patients and may increase the risk of certain anesthetic or nerve-related complications, especially in people with higher body weight. The new supine SARA technique could make surgery faster, safer, and less painful, but it has not yet been tested in a randomized study.

This is the first clinical trial designed to directly compare these two approaches in patients with small and localized kidney cancers (tumors ≤7 cm, stage cT1).

The study will include 124 patients treated at ASST Grande Ospedale Metropolitano Niguarda in Milan, Italy - a leading center in robotic urologic surgery.

Study Objectives

Primary Objective:

To compare the outcomes of RAPN performed with the SARA approach versus the standard flank approach in achieving a "trifecta outcome," defined as:

• No intraoperative adverse events;
• Negative (cancer-free) surgical margins;
• Hospital discharge on postoperative day 1.

Secondary Objectives:

• To compare both approaches according to the rate of achievement of two out of three outcomes, and according to each outcome composing the trifecta separately.
• To evaluate postoperative recovery, including pain scores, time to first walk, time to first flatus, total use of pain medication, and readiness for discharge.
• To compare the rates and severity of postoperative complications within 30 days after surgery.
• To assess surgical parameters such as total operative time, ischemia time, and blood loss.
• To analyze functional outcomes, such as kidney function recovery (Δ eGFR at 30 days).

Study Design This is a prospective, single-center, randomized controlled trial conducted at the Department of Urology, ASST Grande Ospedale Metropolitano Niguarda, Milan, Italy.

Eligible participants will be randomly assigned 1:1 to one of two groups:

Group A (Control): Standard flank approach (transperitoneal or retroperitoneal) using the Da Vinci SP system. Patients are positioned laterally (on their side) with the operative flank elevated at a 12-15° angle. The Da Vinci SP robotic system is docked either transperitoneally or retroperitoneally through a single access port. The tumor is resected and kidney reconstruction is performed according to standard RAPN procedures Group B (Experimental): Supine anterior retroperitoneal approach (SARA) using the Da Vinci SP system. Patients are positioned supine with a mild Trendelenburg tilt (0°-10°). A retroperitoneal space is created through an anterior incision, providing direct access to the kidney without repositioning. The same Da Vinci SP system and standard nephron-sparing techniques are used.

Both groups follow identical perioperative protocols for anesthesia, analgesia, and postoperative care.

Population Adults (age 18 or older) with a single kidney tumor measuring up to 7 cm, who are eligible for robotic partial nephrectomy with the Da Vinci SP system, may be invited to participate. Patients with kidney tumor more than 7 cm or advanced tumors infiltrating the surroinding tissues, solitary kidneys, previous kidney surgery on the same kidney, or severe kidney disease will not be eligible.

• Age ≥ 18 years;
• Presence of a single, unilateral, primary renal mass ≤ 7 cm in diameter (clinical stage cT1) documented CT scan
• No evidence of systemic disease or lymph node involvement;
• Candidate for robot-assisted partial nephrectomy using the Da Vinci SP platform;
• Signed informed consent
• Absence of solitary kidney status
• No previous partial nephrectomy/ies on the same kidney
• Absence of preoperative chronic kidney disease (CKD) stage 5
• Absence of any condition that makes mandatory or significantly more adequate the choice of a specific approach over the others (e.g., multiple previous major abdominal surgeries, horseshoe kidney, presence of stomas)