Surgery for rectal cancer

Introduction

Rectal cancer is defined as adenocarcinoma within 15 cm of the anal verge, and accounts for around 30% of colorectal cancers. There were 14 555 cases of rectal cancer in 2017 in the UK. Surgical excision remains the primary treatment modality for rectal cancer, with selected application of neoadjuvant therapy with radiotherapy, chemoradiotherapy or chemotherapy for advanced cases. Surgery is technically challenging as a result of operating within the bony confines of the pelvis and the necessity to undertake anastomoses in the depths of the pelvis, particularly with the increasing prevalence of obesity. The role of total mesorectal resection in reducing local recurrence is firmly established, ^, however, the optimal approach to radical resection, whether open, laparoscopic, robotic or transanal total mesorectal resection (ta-TME) remains controversial.

Surgery may result in significant short-term morbidity, including anastomotic leak, and the longer-term impact on quality of life is now increasingly recognised. This includes impairment of genitourinary and bowel function with low anterior resection syndrome.

Objectives of surgery

There are three main aims of surgery:

• To maximise the potential for cure by removal of the local tumour with clear resection margins, including all the draining lymph nodes

• To avoid a permanent colostomy, if feasible in terms of oncological and functional outcomes

• To maintain functional outcomes and quality of life, including bowel and genitourinary function.

Every patient should be discussed in a multi-disciplinary meeting, with relevant staging investigations, to determine the optimal management plan, including the need for neoadjuvant therapy. This should include the extent of resection required and the approach to be used. Radical resection of rectal cancer is major surgery and is associated with morbidity and mortality. Mortality is determined by patient factors, tumour factors, and surgeon factors, with an elderly patient over 80 years with significant co-morbidities having a mortality risk of 6–16% as compared to a younger patient having a mortality of 1–8%. There is increasing evidence that assessment and optimisation of patient’s fitness pre-operatively, including the use of prehabilitation, improves post-operative outcome.

Multi-disciplinary meeting

Management of rectal cancer requires a multi-disciplinary approach and formal investigation and discussion in a multi-disciplinary meeting is essential. The members of the multi-disciplinary team should include colorectal surgeons, gastrointestinal radiologists, radiation oncologists, medical oncologists, pathologists and specialist nurses. The required investigations are listed in Box 5.1 and are important to determine the local extent and relationship of the primary tumour, determination of any local and locoregional lymphatic spread and the presence of distant disease.

Circumferential resection margin and local recurrence

The importance of the circumferential resection margin (CRM) of the rectum is well recognised and is intimately associated with the risk of local recurrence. Quirke et al. identified that tumour involvement of the resection margin of the resected rectum significantly increased the risk of development of local recurrence, in a period when the risk of local recurrence following rectal resection was up to 32%. At a similar time, Heald was demonstrating exceptional low local recurrence rates following rectal cancer resection and advocating the importance of sharp dissection of the rectum in the pelvis and the preservation of the fascia propria, the natural ‘embryological’ envelope, around the rectum. Through this approach, the risk of a resection margin involved by the local tumour, and hence one of the factors leading to local recurrence, can be significantly reduced. This finding was confirmed through training programs in total mesorectal excision in a number of countries.

The relationship of the primary tumour to the fascia propria is one of the key determinants of the management plan for specific rectal tumours. It is related to both the tumour stage and tumour position within the rectum. For example, a T2 tumour in the mid-rectum will be well away from the CRM as it has not penetrated through the muscularis propria of the rectum and is surrounded by the fatty mesorectum around the rectum. The same T2 tumour, if very low in the rectum in the muscle tube at the point beyond where the mesorectum is present, will be very close to the CRM. Whilst the CRM can be threatened by the local extent of the primary tumour, it can also be threatened by tumour deposits in involved mesorectal lymph nodes, or deposits of extra-mural venous invasion (EMVI) by tumour, which must all be assessed when determining the risk to the circumferential resection margin.

The key tool for pre-operative assessment of the CRM is the pelvic MRI scan.

Fundamental work by Brown ^, and Beats-Tan demonstrated the predictive value of the MRI in determining the relationship of the rectal tumour to the CRM; tumours within 1 mm of the fascia propria are considered to threaten the CRM. It does allow accurate T staging of the primary tumour, but the relationship of the tumour to the CRM is much more important when determining management. The MRI can also identify tumour involvement of mesorectal lymph nodes and the presence of extra-mural venous invasion in the mesorectum. More recently, the potential importance of pelvic sidewall lymph nodes has been highlighted and these can be identified and measured on pelvic MRI.

Neoadjuvant therapy

Definitive description of the application and options for neoadjuvant therapy are described elsewhere in this book. In brief, rectal tumours considered to threaten the CRM or have high-risk features such as mesorectal or pelvic sidewall nodal involvement, or EMVI, may benefit from neoadjuvant therapy, whereas early stage disease can be treated with surgery alone. Selective application of neoadjuvant therapy is important as it does have negative longer-term functional impacts.

Patient optimisation and prehabilitation

Surgery for rectal cancer is major surgery and advances in anaesthesia and surgical technique have made surgical intervention safer and more accessible for patients with rectal malignancies. Patients are now older and have increasing co-morbidities, including obesity. Post-operative complications in patients undergoing major abdominal surgery are seen in up to 30% of cases, and even without complications, a reduction in functional capacity during the first post-operative month is seen in one-third of patients. Furthermore, post-operative fatigue has been demonstrated to be associated with the pre-operative functional status, particularly affecting patients with poor pre-operative exercise capacity, the elderly, the nutritionally deplete and those with an associated malignancy. ‘Prehabilitation’ of the surgical patient is the pre-operative optimisation of functional capacity before an incoming stressor. This typically occurs between the diagnosis and elective surgical intervention. Optimisation of patients with malignant disease poses an extra set of challenges because of the functional decline associated with neoadjuvant therapy. Patient-centred risk assessment can identify multiple factors that can be optimised in a tailored prehabilitation program ( Box 5.2 ).

Cardiopulmonary exercise testing is the gold standard for evaluating functional capacity and plays an essential role in pre-operative risk stratification. Interventions such as exercise therapy, optimisation of nutrition and immunonutrition, abstinence of smoking and alcohol, haematinic optimisation and psychological support have been investigated in the surgical population and have demonstrated benefits in isolated studies. Prehabilitation has been demonstrated to improve physical fitness and reduce morbidity in patients with rectal cancers undergoing neoadjuvant therapy.

Immediate preparation for surgery should include bowel preparation with oral antibiotics, which have demonstrated to reduce surgical site infection. Prophylactic intravenous antibiotics should be given at induction and thrombophylactic therapy with intra-operative intermittent calf compression and post-operative low-molecular-weight heparin should be used. An Enhanced Recovery after Surgery program (ERAS) should be used to reduce post-operative complications and shorten length of hospital stay ( Box 5.3 ).