Preoperative 5-fluorouracil-based radiochemotherapy (RCT) followed by quality assessed total mesorectal excision (TME surgery) are the two most important elements of multimodal treatment for patients with locally advanced rectal cancer (UICC stages II and III). The optimum sequence of these neoadjuvant modalities complemented by adjuvant (postoperative) chemotherapy, has been addressed in several randomised trials. Especially within the trials of the German Rectal Cancer Study Group (GRCSG), preoperative RCT has been shown to be superior to postoperative treatment for a variety of endpoints (pathologically confirmed complete tumour remission (pCR), RCT-induced tumour regression, R0 resection rates (including circumferential resection margins) and long-term locoregional control). This neoadjuvant multimodal strategy has decreased the 5-year and 10-year local recurrence rates below 10%, and the development of distant metastases (e.g., 35% to 45% liver metastases) remains the predominant reason for failure. Furthermore, approximately 25% of patients do not receive adjuvant chemotherapy, mainly due to surgical complications, patients' refusal or the investigator's discretion. Thus, today, integrating more effective systemic therapy into (preoperative) multimodal regimens is the most accepted challenge! But from the clinical point of view this demand is also a dilemma. The question to be addressed is how and when to apply intensified systemic therapy with adequate dosage and intensity as well as acceptable treatment-associated toxicity. The increase of therapeutic options requires valid predictive biomarkers that may help to stratify patients into regimens associated with low toxicity (5-FU monotherapy alone) or into more intensified treatment for better long-term outcome. In summary, the use of biomarkers for individualised risk-adapted treatment is one of the most promising areas of clinical investigations, not only in rectal cancer. The assessment of individual tumour response, toxicity, and prognosis during multimodal treatment of rectal cancer as a model of a very common solid tumour offers radiooncologists, surgeons, pathologists, gastroenterologists as well as oncologists immense insights into the under-standing of tumour biology.