In this trial the investigators want to examine and compare oncological and surgical outcomes of two surgical techniques in a prospective, randomised, single-blind trial. Therefore the investigators are going to include 30 patients with a renal mass who need surgical treatment. When they fulfill the inclusion criteria they get randomised either for robot-assisted partial nephrectomy or laparoscopic partial nephrectomy. Primary endpoint is the oncological outcome (residual tumor classification, TNM classification), secondary endpoints are operation time, time of ischemia, blood loss, pain after surgery, kidney function, complications and hospital stay.

All patients taking part in the study are first given a R.E.N.A.L. nephrometry score. Based on that score they are allocate to either of :

cohort I (low complexity of the tumour) or cohort II (intermediate complexity of the tumour).

Thereafter, the patient will be randomly placed into either to laparoscopic partial nephrectomy or robotic-assisted partial nephrectomy. Both these surgical techniques are well established and standardized procedures to remove a renal mass.

Preoperatively, the preparation is nearly the same for both techniques. The patient is positioned in flank position with the affected side up.

Thereafter:

Pneumoperitoneum is achieved with a Veress needle and trocars which are placed under direct vision. The only difference between the two techniques is the number of trocars, performing the laparoscopic partial nephrectomy three or four ports are used, performing the robotic-assisted partial nephrectomy five ports are used.

Intraabdominal, the kidney is exposed by incising along the Toldt line to moblize the colon. After exposing the ureter and the gonadal vein dissection is continued proximally toward the renal hilum. Following this, Gerota's fascia is incised to expose the tumour and the surrounding renal capsule. Now the renal artery has to be clamped to avoid bleeding followed by excision of the tumour. The surgery takes about three hours, the complication rate is more the same for both techniques.

Primary endpoint is the resection margin to see if there are any difference between the two surgical techniques.

Information about the resection margin and pathological staging will be given through our pathological department. The histological examination normally takes about five to seven days.

Further parameters are taken by following schema:

Information about age, sex, body mass index, other diseases and medication is documented on the day of inpatient admission.

Blood samples for haemoglobin and kidney function are taken at the day of inpatient admission, four hours after surgery, first day after surgery and the day of discharge from hospital.

The duration of surgery is documented throughout the operative protocol. R.E.N.A.L Nephrometry score is evaluated preoperative, to be able to compare the complexity of surgery.

Renal ischemia is documented throughout the operative protocol. Blood loss is documented during surgery. Pain is documented with the aid of the visual analogue scale (VAS Scale). This will be evaluated four hours after surgery, day one after surgery, day two after surgery and on the day of discharge from hospital.

Complications are documented with the aid of the clavien-dindo classification. Three follow-ups will be performed. The first follow-up will be held two weeks after surgery to discuss the histological result and examine haemoglobin, kidney function and pain. The second follow-up will be held six months after surgery, the third follow-up 12 months after surgery. At this time a re-examination again haemoglobin and kidney function will be performed as well as a computed tomography.

Inclusion Criteria:

• minimum age of 18 years
• solid renal mass suspicious for renal cell carcinoma or at least Bosniak III cyst
• signed informed consent

Exclusion Criteria:

• performed kidney surgery at the same side
• Pregnancy
• RENAL Nephrometry score III

single-blinded