AKT · Gastroenterology/Colon & rectum

Colorectal cancer

Colorectal adenocarcinoma (adenoma–carcinoma sequence; FAP/Lynch in inherited disease)

Overview

Adenocarcinoma of the colon/rectum — the third commonest cancer — arising via the adenoma-carcinoma sequence. Presentation differs by side: LEFT/rectal (change in bowel habit, PR bleeding, tenesmus, obstruction) vs RIGHT (iron-deficiency anaemia, weight loss, mass — often silent). Screened by FIT (faecal immunochemical test). Diagnosed by colonoscopy + biopsy; staged (TNM/Dukes); treated by resection ± chemo/radiotherapy. Inherited: FAP (APC) and Lynch (HNPCC).

Recognise

LEFT-sided/rectal: change in bowel habit (looser/more frequent), PR bleeding/mucus, tenesmus, obstruction (apple-core)
RIGHT-sided: IRON-DEFICIENCY anaemia, weight loss, fatigue, right-sided mass — often presents late/silently
Tenesmus/rectal mass (rectal cancer); hepatomegaly (mets); inherited — FAP (hundreds of polyps, APC), Lynch/HNPCC (also endometrial/other)

Red flags

2-week-wait referral: age ≥40 with weight loss + abdominal pain; ≥50 with rectal bleeding; ≥60 with iron-deficiency anaemia or change in bowel habit; ANY age with a positive FIT or rectal/abdominal mass
Obstruction/perforation → emergency

Differentials & how to tell them apart

Diverticular diseaseleft-sided pain/bleeding — colonoscopy after settling to exclude cancer

Haemorrhoidsfresh PR bleeding but no change in habit/anaemia/mass — still investigate red flags

IBDyounger, inflammatory pattern; long-standing colitis itself raises cancer risk

IBSno red flags, normal FIT/calprotectin

Investigations

COLONOSCOPY + biopsy (diagnostic); CT colonography if colonoscopy unsuitable. FIT (screening/symptomatic triage). Staging CT chest/abdomen/pelvis, MRI rectum (rectal cancer), CEA (baseline/monitoring); FBC (anaemia).

Management

Colonoscopy + biopsy → surgical resection ± (neo)adjuvant chemo/radiotherapy

1Refer on the 2-week-wait pathway for red-flag symptoms or a positive FIT; colonoscopy + biopsy, then CT/MRI staging.Gate: Right-sided cancers present as IRON-DEFICIENCY ANAEMIA (not bleeding) — investigate unexplained iron-deficiency anaemia in older patients with colonoscopy; FIT triages symptomatic patients into the urgent pathway
2Resection (with stoma as needed) + stage-based (neo)adjuvant therapy (neoadjuvant chemoradiotherapy for rectal cancer); CEA/colonoscopic surveillance; genetics for FAP/Lynch.

Surgical resection (colectomy / anterior resection / APR) — primary curative treatment ± stoma

Adjuvant chemotherapy (FOLFOX) / neoadjuvant chemoradiotherapy (rectal) — per stage; rectal cancer often gets neoadjuvant therapy

Palliative chemo ± biologics / stent — metastatic/obstructing disease

Key points

Left = change in habit + PR bleeding + apple-core obstruction; Right = iron-deficiency anaemia + weight loss (silent). FIT triages; colonoscopy diagnoses. Think FAP (hundreds of polyps) and Lynch (+ endometrial cancer) in young/family-history cases.

Monitor & prognosis

CEA, surveillance colonoscopy/CT; stoma care.

Good if early (Dukes A); stage-dependent.

Source: NICE NG151; bowel-cancer screening (FIT)