Rectal cancer
ANATOMY AND EPIDEMIOLOGY
Rectal cancer is usually adenocarcinoma arising in the rectum, conventionally within about 15 cm of the anal verge on rigid/flexible endoscopic measurement. The rectum lies within the pelvis; its mesorectum contains vessels, lymphatics and nodes surrounded by the mesorectal fascia. The circumferential resection margin (CRM) and relation to sphincters, peritoneal reflection and pelvic organs are central to treatment planning.
RISK FACTORS AND PATHOGENESIS
Risk factors overlap with colorectal cancer: age, family history, Lynch syndrome, FAP, prior adenomas, inflammatory bowel disease, obesity, smoking, alcohol and dietary factors. Most tumours develop through adenoma–carcinoma or serrated pathways. Local spread occurs through the bowel wall and mesorectum; lymphatic spread follows superior rectal and pelvic pathways, while distant metastases commonly involve liver and lung.
CLINICAL FEATURES AND EXAMINATION
Symptoms include rectal bleeding, mucus, tenesmus, urgency, altered stool calibre, change in bowel habit, incomplete evacuation, pelvic pain, weight loss and iron-deficiency anaemia. Low tumours may cause pain or sphincter dysfunction. Digital rectal examination assesses distance from anal verge, circumferential extent, mobility, fixation and relation to sphincters. Examine abdomen and inguinal nodes when appropriate.
DIAGNOSIS AND STAGING
Colonoscopy with biopsy confirms histology and checks for synchronous lesions. Baseline tests include FBC, renal/liver function and CEA. High-resolution pelvic MRI is the key local staging test, assessing T stage, mesorectal fascia/CRM, extramural vascular invasion and nodes. CT chest/abdomen/pelvis assesses distant metastases. Endorectal ultrasound may help stage selected early lesions. MMR/MSI testing is important for hereditary assessment and treatment selection.
TREATMENT
Management is multidisciplinary and depends on stage, height, sphincter involvement, MRI risk features, fitness and patient preference. Early favourable T1 lesions may be suitable for local excision (transanal endoscopic microsurgery/TAMIS) if strict criteria are met. Most operable cancers require total mesorectal excision (TME): low anterior resection with anastomosis for suitable tumours or abdominoperineal resection (APR) with permanent colostomy when sphincter preservation is not oncologically/ functionally safe. Locally advanced disease commonly receives neoadjuvant radiotherapy/chemoradiotherapy or total neoadjuvant therapy before TME. Selected complete clinical responders may enter structured watch-and-wait programmes in expert centres. Metastatic disease is treated with systemic therapy and selected metastasectomy/ablation.
COMPLICATIONS AND FOLLOW-UP
Complications include obstruction, bleeding, perforation, local recurrence, liver/lung metastases and pelvic sidewall invasion. Treatment may cause anastomotic leak, low anterior resection syndrome, urinary/sexual dysfunction, stoma complications and pelvic radiation effects. Surveillance includes clinical review, CEA, imaging and colonoscopy according to stage and guidelines.