Bowel Cancer Screening

Colorectal cancer (CRC) is the second most common cause of cancer death in Australia (fourth most common cancer overall — ~15,367 diagnoses and 5,307 deaths in 2023). Early diagnosis is associated with excellent survival, but currently less than 40% of Australian bowel cancers are detected early. This page covers asymptomatic screening; for a symptomatic patient, go straight to the red-flag/symptom-triage section below.

Screening pathways

Bowel cancer screening has two arms:

• Mass/population screening — the National Bowel Cancer Screening Program (NBCSP), for asymptomatic average/near-average-risk people only.
• Case-finding/targeted screening (iFOBT or colonoscopy) — for people with a significant family history, based on risk category below.

National Bowel Cancer Screening Program (NBCSP)

• Posted automatically every 2 years from age 50 to 74.
• From 1 July 2024: eligible people aged 45–49 can request their first kit to be mailed to them (previously the automatic start age was 50) — a genuine and recent expansion, not yet reflected in the automatic-mailout age itself.
• Uses an immunochemical FOBT (iFOBT) — 2 samples on separate days, no dietary/ medication interactions, results go to patient + NBCSP register + nominated GP.
• Biennial iFOBT reduces CRC mortality by ~16%.
• Colonoscopy is not a recommended screening test for average-risk patients — discourage its inappropriate use as a primary screening tool; discuss the comparative harms/benefits (per 100,000 screened: FOBT pathway causes far fewer bleeds/perforations/deaths overall than a colonoscopy-for-everyone strategy, because far fewer people actually need the invasive test).
• Advise patients to delay testing if: <3 days since menses ended, active bleeding haemorrhoids, recent/upcoming colonoscopy, or visible blood in urine/stool bowl.

Family-history risk categories

Category	Family history	Screening
1 — near-average risk (~95–98% of the population)	No family history of CRC, or only 1 first-degree relative (± 1 second-degree) diagnosed ≥60yrs	iFOBT every 2 years, age 45–74. Routine colonoscopy not recommended unless FOBT positive.
2 — moderate risk	1 first-degree relative diagnosed <60yrs; or 2 first-degree relatives at any age; or 1 first-degree + ≥2 second-degree relatives at any age	Colonoscopy every 5 years, starting 10 years before the youngest affected relative’s age or 50yrs (whichever earlier), to age 74. iFOBT every 2 years, age 45–74. CT colonography if colonoscopy contraindicated.
3 — high risk	≥2 first-degree + 1 second-degree relative (≥1 diagnosed <50yrs); ≥2 first-degree + ≥2 second-degree relatives at any age; ≥3 first-degree relatives at any age; known high-risk gene mutation (Lynch syndrome, FAP)	Colonoscopy every 5 years, starting 10 years before the youngest affected relative’s age or 40yrs (whichever earlier), to age 74. Consider genetic-centre referral.

Patients with a known or suspected familial syndrome (below) have a potentially much higher risk than the table implies — refer for genetic risk assessment.

Familial syndromes to consider

Familial adenomatous polyposis (FAP), Lynch syndrome (formerly HNPCC), MUTYH- associated polyposis, serrated polyposis syndrome, Peutz-Jeghers syndrome, juvenile polyposis syndrome. Suspect a high-risk familial syndrome if: a relative is a confirmed carrier of a pathogenic gene the patient hasn’t been tested for; a relative has multiple CRCs or FAP; or ≥3 first-/second-degree relatives have a Lynch-associated cancer (endometrial, ovarian, gastric, small bowel, renal pelvis/ureter, biliary tract, brain) with ≥1 diagnosed <55yrs.

Reducing colorectal cancer risk (discuss with all patients)

• Complete the NBCSP iFOBT every 2 years if aged 45–74.
• Consider low-dose aspirin (100–300mg/day) after weighing risks/benefits — guidelines recommend at least 2.5 years, starting somewhere between age 50–70.
• High-fibre diet (vegetables, fruit, whole grains); minimise red/processed/ barbecued/grilled meat; maintain a healthy weight; regular physical activity; limit alcohol; don’t smoke.

Early-onset colorectal cancer (EOCRC) — a genuinely rising problem

EOCRC (diagnosed <50yrs) has risen from 7.6% of all CRC in 1992 to 11.1% in 2021, and the proportion of EOCRC occurring before age 40 has risen from 30% (1982–86) to 44% (2017–21). This drove the 2024 NBCSP eligibility expansion to 45yrs — there is evidence supporting a further reduction to age 40, not yet implemented.

• Younger patients present later — one Australian study found 81.9% of EOCRC is Stage III/IV at diagnosis, partly because this group is missed by the NBCSP.
• Hereditary syndromes (FAP, Lynch, other germline mutations) account for ~35% of EOCRC, compared with only ~10% of CRC overall — refer any EOCRC diagnosed <35yrs for genetic screening, even without an apparent family history.
• ~50% of EOCRC has no identifiable genetic/familial cause and is sporadic, attributed to Western dietary patterns (processed/red meat, low fibre, high glycaemic load), alcohol, smoking, sedentary lifestyle, and obesity — particularly early-life/adolescent obesity. Protective factors: whole grains, fruit/vegetables, folate, calcium, vitamin D, fish, physical activity, aspirin, NSAIDs.
• EOCRC may be a biologically distinct entity — more aggressive, more often distal/rectal — so don’t assume a young patient’s presentation is reassuring.
• People aged 40–44 with no significant family history can also be referred for biennial iFOBT via a Medicare-subsidised pathway, outside the automatic NBCSP mailout — but that screening outcome isn’t stored centrally by the NBCSP, so track completion in your own recall system.
• National iFOBT participation is only around 41%, which is an area worth actively improving rather than relying on the automatic mailout alone.

Symptomatic patients — red flags (do not screen, investigate)

If any of these are present, this is not a screening scenario — proceed straight to diagnostic work-up/referral, regardless of age or FOBT status:

• Unexplained rectal bleeding (with or without mucus)
• Altered bowel habit (loose motions or constipation) for >6 weeks
• Unexplained iron deficiency anaemia
• Rectal or abdominal mass
• Unexplained weight loss
• Unexplained new abdominal pain

Possible causes of rectal bleeding: diverticular disease (most common cause of significant bleeding), haemorrhoids (most common cause of bleeding overall), anal fissure, angiodysplasia, ischaemia, neoplasia, inflammatory (infective or IBD), iatrogenic (e.g. post-polypectomy). Massive upper GI bleeding can rarely present as rectal bleeding.

Assessment

• History: personal history of CRC/polyps/adenomas/IBD; bleeding-risk medications; comorbidities affecting anaesthesia/sedation fitness; prior colonoscopy findings.
• Examination: digital rectal exam (mass, ulceration), abdominal exam (mass, hepatomegaly, inguinal nodes), signs of anaemia/jaundice, weight.
• Investigations: FBC, ESR, iron studies (any unexplained anaemia needs a cause). FOBT can help triage urgency in symptomatic patients but does NOT replace colonoscopy referral — a negative FOBT in a symptomatic patient is not reassuring. Consider LFTs, CRP, coeliac serology, coagulation studies, faecal calprotectin (MBS-funded if <51yrs, symptoms >6 weeks, infective causes excluded, no red flags — helps distinguish IBS from IBD but doesn’t rule out cancer; not specific if rectal bleeding is present). Abdominal imaging if a mass or pain.

Referral urgency (NSW state-wide criteria)

Urgent (colonoscopy within 30 days) if any of:

• Positive NBCSP FOBT.
• Age ≥40 + positive FOBT + rectal bleeding/bowel-habit change/lower GI symptoms/ unexplained anaemia.
• Age ≥50 + negative FOBT but rectal bleeding/bowel-habit change/lower GI symptoms/unexplained anaemia.
• Any age with ≥5% unexplained weight loss in 1 month or ≥10% in 6 months.
• Any age with imaging concerning for colorectal or upper GI cancer.

Non-urgent (still needs colonoscopy, less time-critical) if:

• Age <39 + positive FOBT + symptoms above; or age 40–49 + negative FOBT + symptoms; or age <39 + negative FOBT + symptoms; or age <49 with bowel-habit change + elevated faecal calprotectin (>100µg/g).
• Family history suggestive of a hereditary syndrome, or moderate/high CRC risk category (age for colonoscopy depends on the syndrome).
• Personal history of polyps/CRC due for repeat surveillance.

Continue monitoring while awaiting colonoscopy — advise patients to report any new symptom lasting >6 weeks, and escalate if status changes. Start iron replacement if iron deficiency is found — it does not affect colonoscopy results and improves surgical outcomes if needed.

Colorectal polyp surveillance (after polypectomy)

Most patients ~50% of Australians will develop a bowel polyp; most are asymptomatic. Hyperplastic polyps are not precancerous and don’t need specific follow-up unless >10 in number or ≥10mm. Adenomatous polyps (adenomas) are precancerous (10–20 year lead time to cancer) and need surveillance after removal.

First surveillance colonoscopy — conventional adenomas

Findings	Interval
1–2 small (<10mm) tubular adenomas, no high-grade dysplasia (HGD)	10 years (or return to FOBT screening after 4yrs if 1–2 diminutive <6mm adenomas; consider 5yrs if male + metabolic syndrome)
1–2 adenomas <10mm with HGD/villosity, or 3–4 tubular adenomas <10mm without HGD	5 years
Any polyp ≥10mm with 1–2 adenomas, or 3–4 tubular adenomas ≥10mm without HGD; or 3–4 <10mm adenomas with HGD/villosity	3 years
5–9 tubular adenomas, all <10mm, no HGD	3 years
5–9 polyps with ≥1 ≥10mm (± HGD/villosity); or ≥10 adenomas	1 year (consider familial-predisposition referral if ≥10 polyps removed)

Serrated polyps (sessile serrated adenomas, traditional serrated adenomas, large ≥10mm hyperplastic polyps) follow a parallel but distinct interval table — broadly, 1–2 low-risk serrated polyps = 5 years, escalating to 1 year for ≥5 polyps or any with dysplasia/TSA features; combined serrated + high-risk conventional adenoma findings default to the shorter (1–3 year) intervals. Large sessile/laterally-spreading lesions: 12 months after en-bloc excision, 6 months (then 12–18 if clear) after piecemeal excision.

Second surveillance colonoscopy: interval is based on the findings of the two most recent procedures combined — no formal guideline exists beyond this point, but the same principle (findings from the 2 most recent scopes guide the next interval) applies indefinitely.

Patients aged ≥75yrs: the adenoma-to-cancer lead time (10–20yrs) approaches or exceeds average life expectancy at this age, and procedural risk rises — for ages 75–80, calculate a Charlson comorbidity score: ≤4 → consider surveillance; >4 → not recommended. Over 80yrs: surveillance colonoscopy is not recommended.

Post-resection surveillance (past colorectal cancer)

• Colonoscopy at 1 year post-resection, unless a complete postoperative colonoscopy was already done sooner.
• If normal at 1 year → next colonoscopy at 6 years, then 11 years (i.e. 1/6/11-year schedule), unless family history indicates earlier specialist- directed surveillance.
• If it reveals cancer, refer urgently back to the treating specialist team; if it reveals adenomas, follow the polyp-surveillance table above.
• Family members should still be risk-stratified and screened per the family- history table above.

Staging, treatment and prognosis (for patient discussion)

TNM staging (T: depth of tumour invasion through the bowel wall; N: regional lymph node involvement; M: distant metastasis) determines the 5-year survival: Stage I ~93%, Stage II ~85%, Stage III ~64–83% (with adjuvant chemotherapy adding a 10–15% survival benefit), Stage IV ~44% (systemic chemotherapy is usually palliative; isolated hepatic metastases are potentially curable by resection in a minority of cases).

Familial CRC genes: Lynch syndrome (dominant MLH1/MSH2/PMS2 mutation, associated with colorectal/endometrial/ovarian/gastric/renal-pelvis/ureteric/ small-bowel/biliary/brain cancers, ~6% of all CRC) and FAP (dominant APC mutation, multiple colonic adenomas, ~1% of CRC). Features raising suspicion: multiple affected relatives on one side of the family, multiple CRCs in one person, CRC <50yrs, other Lynch-related cancers, >20 colonic adenomas, adenomas <30yrs. Three-generation family history is key to identifying candidates for genetic testing — genetic risk assessment itself is a specialist-level test, not a GP task.

Patient counselling for a new diagnosis: surgery is typically 1–4 hours with 5–10 days’ admission, 6 weeks off work, up to 8 weeks before vigorous activity. Average mortality risk in a fit patient <80yrs is 1–2%; right-sided resections carry ~2% anastomotic leak risk; distal/rectal lesions may need a loop ileostomy. Staging work-up: CT chest/abdomen/pelvis, FBC/EUC/LFT/CEA, baseline ECG.