**2. Early rectal cancer (ERC)**

### **2.1 Definition of ERC**

The definition of ERC remains somewhat controversial but is based on the TNM classification. Overall, it is characterised by invasive adenocarcinoma spreading into, but not beyond, the submucosa or muscularis propria, that is, a TNM of T1 or T2, N0 and M0 [4, 5]. Clinically, ERC may present as a polypoid carcinoma, a focus of malignancy within a large pedunculated or sessile adenoma, or a small ulcerating adenocarcinoma [6]. ERCs have a smaller chance of metastasis to local lymph nodes, due to the lack of lymphatics within the mucosa and therefore are potentially treatable without major surgery that excises the mesorectum to mitigate loco-regional spread [5]. However, not all ERCs are the same and treatment strategies must be determined by prognostic factors such as differentiation status and depth of invasion [1, 5].

At publication, there was no international consensus on the definition of ERC, though it is fundamental in discussing treatment options and prognostication with patients. There are several micro- and macroscopic definitions, however these do not capture the overall clinical impact of the disease. As a result, the European Association of Endoscopic Surgery and the European Society of Coloproctology have defined ERC as "a rectal cancer with good prognostic features that might be safely removed while preserving the rectum and have a very limited risk of relapse after local excision" [5].

As with any cancer, the aim of treating ERC is to offer cure while minimising side effects. This is fundamentally achieved by aiming to preserve the rectum. Organ preservation attempts to mitigate the significant risk of total mesorectal excision (TME) surgery which has a 30-day mortality of 3–7%, morbidity of 35% and risk of poor functional outcomes from low anterior resection syndrome (LARS) of up to 20%. While the evidence supports local excision, TME surgery via anterior resection and

abdominoperineal excisions (APER) remains the mainstay of treatment with the best prospect of cure. Specifically, it removes the mesorectum to aid histological analysis for loco-regional spread and subsequent decisions on adjuvant treatment [1, 7].

### **2.2 History of ERC surgery**

Abdominoperineal resection (APR), described by Miles et al. in 1901, was the standard operation for much of the twentieth century. In the 1970s, high rates of recurrence were recognised but, more so, the complications of any pelvic surgery led to a re-evaluation of the anatomy and embryology by Crapp and Cuthbertson in 'The Book Shelf—William Waldeyer and the Rectosacral Fascia' [8]. This paved the way to revisiting TME surgery, first described by Abel in 1931, and popularised in 1979 by William (Bill) Heald [9]. TME surgery removes the envelop of the lymphovascular mesorectum by following the 'holy' avascular and embryological mesorectal fascia plane. Heald demonstrated a reduction in recurrence, improved survival, and less bladder and sexual dysfunction. TME remains the gold standard for curative surgery worldwide.

Most would agree that TME surgery for ERCs and high-risk adenomas that have a minimal risk of lymphatic or metastatic spread is 'over-treatment', given the risk of significant morbidity. Until the 1980s, local excision of rectal adenomas and ERCs was performed with trans-anal excision (TAE). This involved open excision of the lesion using an anal retractor, but was restricted by poor visibility, confined operating space and suitable for low rectal lesions only. Technical challenges limited complete oncological resection, resulting in high recurrence rates [1].

In 1984, Buess et al. described the novel technique of transanal endoscopic microsurgery (TEM) [10]. This utilised a stereoscopic viewing system within a rigid rectoscope to give the operator 3D binocular view. A specialised insufflation system created a stable pneumorectum, allowing ample workable space, while dedicated microsurgical instruments provided a high level of precision for oncological resections. Initial results endorsed TEM as an effective technique for rectum-sparing resection of adenomas and malignancy, with low rates of recurrence. However, it was not initially popular. Barriers included a steep learning curve, a lack of other minimally invasive surgical techniques, high equipment costs and staff expertise. With the advent of minimally invasive surgery (MIS) in 1989 from the first laparoscopic cholecystectomy and later extended to colorectal surgery, TEM became more acceptable.

Interest grew as technology progressed, including the development of other natural orifice surgeries and single-incision laparoscopic surgery (SILS). In 2008, the technological advances were combined with the TEM concepts to perform Transanal Minimally Invasive Surgery (TAMIS). A single-incision laparoscopic surgery port is inserted into the rectum through which a pneumorectum is established, and laparoscopic instruments can be passed. This technique allows a platform for precise resection, with low cost and routinely available instruments [1].

Radical surgery carries a significant risk of mortality, morbidity and bowel dysfunction [1, 7]. Before attempting an organ preserving approach it is important to distinguish between malignant and benign lesions. Organ preserving surgery demands a multi-factorial considerations. These include surgical experience, pathological stage, anatomical location of tumour, fitness of patient and patient's wishes. Histologically well differentiated adenocarcinomas with the absence of lymphatic invasion, budding, and submucosal invasion <1 mm are associated with low risk of lymphatic spread [11]. As more treatment options became available, decisions became increasingly complex. Multi-disciplinary team meetings specifically for ERCs and significant polyp and early colorectal cancers (SPECC) are becoming more widely established. In the UK, National Institute of Clinical Excellence (NICE) guidance recommends that all TNM stage 1 rectal cancers are discussed within an ERC/SPECC MDT. This includes all pertinent specialists, i.e. surgeon, radiologist, endoscopist, histopathologist, nurse specialists, and oncologists. MDTs do improve rates of complete resection, operative mortality and patient satisfaction outcomes [4, 11].

### **2.3 Investigations for ERC**

### *2.3.1 Colonoscopy*

ERC may present with rectal bleeding or as an incidental finding during screening. At endoscopic evaluation, macroscopic detection of malignant transformation of any polyp is challenging, and more so the features of spread beyond the muscularis propria. The endoscopist aims to identify the classic changes of cancerous potential by examining mucosal irregularity for pinkness, superficial granularity and nodularity, mucosal fading, depressions, or haemorrhagic spots [6]. Other techniques include magnifying colonoscopy to better examine pit-patterns and air transformation by reducing insufflation pressure to locate depressed areas of invasion. For an ERC, narrow-band imaging and dye techniques, (such as indigo carmine) may reveal the loss of circumferential grooves at the margins of normal mucosa [12, 13].

Tissue biopsy is required unless the tumour can be removed completely via endoscopy. Biopsy and histology are essential for staging and management. However, they frequently under-stage disease due to sampling error from superficial or anatomically challenging locations and inter-observer errors in interpretation of histopathology [12]. Furthermore, biopsies can lead to the "non-lifting sign" from fibrosis, making subsequent local excision more challenging. The authors therefore agree with the recommendation that tissue biopsies should be performed at the most suspicious area of the lesion. Also, where malignancy is unlikely and complete excision is not within the remits of the endoscopist's skill set, biopsy should be avoided to allow subsequent success at excision by a more advanced endoscopist, and unhindered by scarring [4].

### *2.3.1.1 Kudo classification*

Macroscopic classification of adenomas, proposed by the Japanese Society for the Study of Cancer of the Colon and Rectum resembles that of gastric tumours (**Table 1**). Adenomas are subdivided into pedunculated or sessile. Around 42–85% of early colorectal cancers are pedunculated and 15–58% sessile. Adenocarcinomas in pedunculated polyps have less potential to infiltrate the submucosal layer [6, 13].
