Rationale and background: Predictive factors are needed to discriminate chemoradiotherapy responders from non-responders and to individualize the treatment regime. Various cytokines play a role in processes affecting tumour growth and metastasis. Furthermore, cytokines might influence treatment response. Various cytokines are abnormally expressed in colorectal cancer patients, are associated with colorectal cancer or determine response to chemoradiotherapy. Therefore the investigators want to investigate whether levels of circulating cytokines could predict response to preoperative chemoradiotherapy in patients with rectal cancer.

Hypothesis: The investigators hypothesis is that the varying levels of circulating cytokines in the blood of rectal cancer patients may predict the response to preoperative chemoradiotherapy.

Study design: This study is an explorative clinical pilot study in which the investigators will collect 4 ml of blood from a selection of rectal cancer patients during a regular venipuncture before, during and after preoperative chemoradiotherapy and before and after surgery. Cytokines will be measured in blood plasma and in tumour and healthy tissue from the resection specimen using multiplex immunoassays. Plasma cytokine measurements will be linked to pathological response to identify which cytokines and corresponding levels can predict response to preoperative chemoradiotherapy for patients with locally advanced rectal cancer. Furthermore, blood plasma cytokine measurements before and after surgery will be compared to evaluate the effect of tumour resection on the immune response. In addition, preoperative blood plasma cytokine levels will be compared with cytokine levels in normal and tumour tissue to test whether circulating cytokine levels are representative for tissue cytokine levels.

Study population: Thirty patients (≥18 years) with locally advanced rectal adenocarcinoma eligible for preoperative chemoradiotherapy (oral capecitabine and 45-50 gray (Gy) in total; fractions of 1.8-2 Gy) and surgery.

Country of recruitment: The Netherlands

Inclusion Criteria:

• Pathohistological diagnosis of locally advanced rectal adenocarcinoma (<15 cm from the anal verge)
• Eligible for preoperative chemoradiotherapy (chemotherapy: oral capecitabine / radiotherapy: 45-50 Gy in total; fractions of 1.8-2 Gy) and surgery (stage 2 or 3 rectal cancer)
• Planned to undergo a venipuncture for a regular blood collection during preoperative chemoradiotherapy, before, and after surgery
• Written informed consent
• Age ≥18

Exclusion Criteria:

• Age <18
• Serious adverse events during preoperative chemoradiotherapy
• Use of corticosteroids and/or immunosuppressive drugs during or 1 month prior to the study
• Other malignancies in medical history
• Previous pelvic radiotherapy and/or chemotherapy
• Confirmed bacterial or viral infection during the study or 3 months prior to the study

Patients with locally advanced rectal cancer diagnosed in St. Antonius Hospital Nieuwegein and Utrecht, 18 years or older, selected for preoperative chemoradiotherapy (chemotherapy: oral capecitabine; radiotherapy: 45-50 Gy in total; fractions of 1.8-2 Gy) and surgery. Rectal carcinoma is defined as <15 cm from the anal verge. They are already routinely planned to undergo a regular venipuncture for blood collection and intravenous needle before surgery.