A Scoping Review of the Implications and Applications of Body Composition Assessment in Locally Advanced and Locally Recurrent Rectal Cancer.

: A strong body of evidence exists demonstrating deleterious relationships between abnormal body composition (BC) and outcomes in non-complex colorectal cancer. Complex rectal cancer (RC) includes locally advanced and locally recurrent tumours. This scoping review aims to summarise the current evidence examining BC in complex RC. : A literature search was performed on Ovid MEDLINE, EMBASE, and Cochrane databases. Original studies examining BC in adult patients with complex RC were included. Two authors undertook screening and full-text reviews. : Thirty-five studies were included. Muscle quantity was the most commonly studied BC metric, with sarcopenia appearing to predict mortality, recurrence, neoadjuvant therapy outcomes, and postoperative complications. In particular, 10 studies examined relationships between BC and neoadjuvant therapy response, with six showing a significant association with sarcopenia. Only one study examined interventions for improving BC in patients with complex RC, and only one study specifically examined patients undergoing pelvic exenteration. Marked variation was also observed in terms of how BC was quantified, both in terms of anatomical location and how cut-off values were defined. : Sarcopenia appears to predict mortality and recurrence in complex RC. An opportunity exists for a meta-analysis examining poorer BC and neoadjuvant therapy outcomes. There is a paucity of studies examining interventions for poor BC. Further research examining BC specifically in patients undergoing pelvic exenteration surgery is also lacking. Pitfalls identified include variances in how BC is measured on computed tomography and whether external cut-off values for muscle and adipose tissue are appropriate for a particular study population.