The intention of the study is to explore metabolic and inflammatory parameters in the pelvis and systemically after abdominoperineal resection (APR) for locally advanced rectal cancer (LARC) in patients that have received radiation therapy before surgery. In this study the inflammatory response after laparoscopic robot-assisted APR for LARC will be compared to results obtained in a recent cohort of patients operated with open APR for LARC, which will serve as the control population.

Locally advanced rectal cancers (LARC) threaten the normal surgical margins and therefore needs neoadjuvant (chemo-) radiotherapy to down-stage the tumor before surgery. The Norwegian Radium Hospital Oslo University Hospital is a regional center for treatment of LARC in the south-eastern part of Norway and treat approximately 80-100 patients in this category annually. About 50 of these patients receive abdominoperineal resection (APR) as the main surgical treatment.

Laparoscopic surgery in LARC has been limited because of difficult dissection with straight instruments outside the normal anatomical planes in the confined space of the pelvis. However, recent papers report on better feasibility and good results in robot-assisted surgery for LARC. In respect to shorter postoperative length of stay for minimally invasive compared to open surgery, reduced inflammation may be the explanation, however, results are not conclusive. Most studies comparing open to minimally invasive surgery in colorectal cancer have had conventional laparoscopy as the minimally invasive group, including studies comparing inflammation after surgery. A study on inflammation after laparoscopic robot-assisted major surgery for bladder cancer has recently been published, but to our knowledge no comprehensive studies have been done with patients with rectal cancer resections. Additionally, there are claims that excessive and/or dysregulated inflammatory response after cancer surgery, worsen oncologic outcome. The need to characterize the inflammatory response after laparoscopic robot-assisted surgery of rectal cancer is thus highly relevant and needed.

The investigators want to analyse inflammatory parameters in plasma and peritoneal fluid in patients undergoing robot-assisted and open surgery for LARC.

Microdialysis is a technique which enables close to real-time monitoring of the tissues and organs of interest. The investigators want to utilize the microdialysis method to describe and monitor metabolic and inflammatory parameters in some patients after extensive robot-assisted oncological surgery for LARC.

The investigators hypothesize inflammatory response differ between patients undergoing open versus robot-assisted surgery.

Inclusion Criteria:

• Patients with primary rectal adenocarcinoma that have received radiation ≥25 Gy to the pelvis.
• operation with APR with laparoscopic robot assisted technique.
• have accepted and signed the consent form.

Exclusion Criteria:

• APR for other reasons

Patients with locally advanced rectal cancer who receive radiotherapy >25 Gy prior to surgery.