8 Chapter 1 Introduction The treatment landscape in rectal cancer Colorectal cancer is the third most prevalent type of cancer in the world and second regarding mortality [1, 2]. Approximately one-third of all colorectal cancers concern rectal cancers. Historically, the management of rectal cancer primarily involved surgical intervention, typically using total mesorectal excision (TME). While surgery remains a fundamental component of rectal cancer treatment, the treatment landscape has evolved into a multidisciplinary approach that encompasses chemotherapy, radiation therapy, targeted therapies, and innovative surgical techniques. In recent years, there has been a specific paradigm shift in treatment towards “organ preservation”. The Brazilian group of Habr-Gama et al. was one of the first to show that approximately one fourth of locally advanced rectal cancers show a complete response after neoadjuvant chemoradiation (CRT), and that surgery could be avoided in these patients without compromising oncological outcomes [3]. Since the introduction of this ‘watchand-wait’ (W&W) approach, research groups from around the world have confirmed that, in carefully selected patients, W&W can be a safe alternative to surgical resection with an important positive impact on quality of life [4-6]. At the same time, studies are now focusing on maximizing neoadjuvant treatment effects to improve response rates and offer more patients the option of organ-preservation. For example, the RAPIDO trail compared standard of care chemoradiation to short course radiotherapy followed by chemotherapy and showed that the percentage of complete responders could be doubled after short course radiotherapy and chemotherapy [7]. Several studies have also shown promising results for ‘total neoadjuvant therapy’ (TNT) that incorporates chemotherapy with CRT. With TNT, studies have shown that a complete response may be reached in up to half of the patients [8]. Finally, studies such as the STAR-TREC and OPERA trial are now investigating the benefit of giving ‘neoadjuvant’ therapy to more early stage tumours that would otherwise be primarily operated, with the aim of achieving organ preservation [9, 10]. Role of imaging and the radiologist Magnetic Resonance Imaging (MRI) has developed into the main diagnostic tool for the primary local staging of rectal cancer and plays a pivotal role to stratify patients into different risk and treatment groups. Based on the MRI assessment of key risk factors such as the local tumour (T) stage, lymph node (N) stage and tumour extension into the anticipated surgical resection plane, patients are stratified as low, intermediate or high risk. This risk stratification determines whether they may undergo immediate surgery or first require neoadjuvant radiation and/or chemotherapy to downstage the tumour. The increased focus on organ-preservation has greatly increased the importance of the radiologist in monitoring patients undergoing neoadjuvant treatment. MRI nowadays
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