Organ Preservation in Locally Advanced Rectal Cancer by Radiochemotherapy Followed by Consolidation Chemotherapy.

Inclusion Criteria:

* Male and female patients with histologically confirmed diagnosis of rectal cancer localized 0 - 12 cm from the anocutaneous line as measured by rigid rectoscopy (i.e. lower and middle third of the rectum)
* Any MRI staged cT3 tumor or any cT1 cN+ or cT2 cN+ with nodal staging according to "SOP MRI"
* Staging requirements: High-resolution, thin-sliced (i.e. 3mm) magnetic resonance imaging (MRI) of the pelvis is the mandatory local staging procedure.
* Cross-sectional imaging of the abdomen and chest to exclude distant metastases.
* Aged at least 18 years. No upper age limit.
* WHO/ECOG Performance Status ≤ 1
* Adequate hematological, hepatic, renal and metabolic function parameters
* Informed consent of the patient

Exclusion Criteria:

* Lower border of the tumor localised more than 12 cm from the anocutaneous line as measured by rigid rectoscopy
* cT4 tumors
* Positive lateral pelvic lymph nodes
* Distant metastases (to be excluded by CT scan of the thorax and abdomen)
* Preexisting fecal incontinence for solid stool
* Preexisting peripheral sensory neuropathy with functional impairment
* Preexisting myelosuppression reflected by a neutrophil count \< 2.000/mm\^3 and/or platelets \< 100.000/mm\^3
* Severe impairment of kidney function with a Creatinin Clearance \< 30 ml/min)
* Prior antineoplastic therapy for rectal cancer
* Prior radiotherapy of the pelvic region
* Major surgery within the last 4 weeks prior to inclusion
* Subject pregnant or breast feeding, or planning to become pregnant within 6 months after the end of treatment.
* Subject (male or female) is not willing to use highly effective methods of contraception according to the "Clinical trial fertility group"
* On-treatment participation in an interventional clinical study in the period 30 days prior to inclusion
* Previous or current drug abuse
* Other concomitant antineoplastic therapy
* Serious concurrent diseases, including neurologic or psychiatric disorders (incl. dementia and uncontrolled seizures), active, uncontrolled infections, active, disseminated coagulation disorder, severe liver function disorders
* WHO/ECOG Performance Status \> 1
* Clinically significant cardiovascular disease (incl. myocardial infarction, unstable angina, symptomatic congestive heart failure, serious uncontrolled cardiac arrhythmia) ≤ 6 months before enrolment.
* Chronic diarrhea (\> grade 1 according NCI CTCAE) Prior or concurrent malignancy ≤ 3 years prior to enrolment in study (Exception: non-melanoma skin cancer or cervical carcinoma FIGO stage 0-1), if the patient is continuously disease-free
* Known allergic reactions on study medication
* Known dihydropyrimidine dehydrogenase deficiency
* Medication inhibitors of the dihydropyrimidine dehydrogenase, such as Brivudin, Sorivudin and its analogues.
* Pernicious anemia or other anemias caused by Vitamin B-12 deficiency.
* Psychological, familial, sociological or geographical condition potentially hampering compliance with the study protocol and follow-up schedule (these conditions should be discussed with the patient before registration in the trial).
* Additionally for hyperthermia cardiac pacemakers and metal implants in the proximity of the pelvis constitute a criterion for exclusion.