Inclusion Criteria:  Patients must be mentally capable of understanding the information given. Patients must give written informed consent. Endoscopically suspected or histologically verified malignant tumor of the rectum or sigmoid colon. Tumor described as passable at index endoscopy. Men or women aged at least 18 years. Case reviewed by MDT (surgery, radiology, oncology). Case considered curable with standard surgical resection. ASA class I-II (Classification of the American Society of Anesthesiology)  Exclusion Criteria:  Indication for neoadjuvant chemoradiation or chemotherapy prior to surgery Uncorrectable coagulation disorder. Patients with ICD or pacemaker units. Ongoing immunosuppressive treatment. Patients with concomitant use of phenytoin. Myocardial insufficiency, defined as NYHA class >2 Concurrent treatment with an investigational medicinal product. Patients with any other clinical condition or prior therapy that, in the opinion of the investigator, would make the patient unsuitable for the study or unable to comply with the study recruitments. Advanced tumor stages, clinical UICC stage IV. Acute surgical resection. Pregnancy Medical history of severe pulmonary disease. Previous cumulative dose of bleomycin exceeding 250mg/m2. BMI > 35 Renal impairment, defined as eGFR <40 ml/min