Stage IIIB Caecal Adenocarcinoma

Clinical Vignette.

A 54-year-old man presents to an oncology clinic in Ile-Ife with a 5-month history of fatigue, 8 kg weight loss and dark stools. Physical examination reveals marked conjunctival pallor and a palpable, non-tender mass in the right iliac fossa.

Laboratory: Hb 6.2 g/dL (microcytic, hypochromic), ferritin 8 ng/mL, CEA 18.5 ng/mL. Liver and renal function are normal.

Colonoscopy and histology: Ulcerated caecal mass; invasive, moderately differentiated adenocarcinoma.

Staging CT (chest, abdomen, pelvis): T3 lesion invading the subserosa with four enlarged pericolic lymph nodes. No hepatic or pulmonary metastases. Clinical stage cT3 N2a M0 (Stage III).

Surgical outcome: Right hemicolectomy. Pathology confirms pT3 N2a (4/16 nodes positive), MSS/pMMR, KRAS/NRAS wild-type.

Discussion Questions

1. Surgical staging and quality metrics. What defines adequate lymphadenectomy in colon cancer resection, and how does node yield directly affect staging accuracy and adjuvant treatment decisions?

2. Adjuvant regimen selection and logistics. Compare 3 months of CAPOX with 6 months of FOLFOX for this patient in terms of disease-free survival equivalence (IDEA collaboration findings), neurotoxicity risk, and cost-effectiveness in out-of-pocket settings.

3. Biomarker dynamics in adjuvant versus metastatic settings. Despite KRAS/NRAS wild-type status, why are anti-EGFR monoclonal antibodies (cetuximab/panitumumab) contraindicated in stage III adjuvant therapy? How would primary tumour sidedness alter your targeted therapy choice if he later develops liver metastases?

4. dMMR/MSI-H clinical implications. If pathology had instead shown dMMR/MSI-H status, how would that alter prognosis, benefit from single-agent fluoropyrimidines, and potential response to immune checkpoint blockade across early and advanced stages?

Discussions.

1. Surgical Staging and Quality Metrics

Adequate lymphadenectomy in colon cancer means examination of at least 12 regional lymph nodesas this is the endorsed standard by the AJCC 8th edition, NCCN and the College of American Pathologists, and it serves as a quality indicator for both the surgeon and the pathologist.

Node yield is more than a number to count. For a right hemicolectomy it reflects a resection taken along the embryological planes, with high ligation of the ileocolic vessels and of the right colic or middle colic branches where relevant. Complete mesocolic excision with central vascular ligation produces higher yields and better oncological outcomes. Yield also depends on the pathologist’s diligence, and fat-clearing techniques help when the first count falls below 12. However it is known that right-sided resections tend to yield more nodes than left-sided ones.

Node yield affects staging accuracy. When too few nodes are examined, node-positive disease is misclassified as stage II, and the patient loses the adjuvant chemotherapy they need. Large population datasets consistently associate higher node yield with better survival, even within node-negative disease, largely because a “negative” result from a small sample is unreliable.

This has direct treatment consequences. In stage II disease, fewer than 12 nodes is itself a high-risk feature that justifies adjuvant chemotherapy. In stage III disease, an inadequate yield can undercount positive nodes and downgrade N2 to N1, moving a patient from the IDEA high-risk group (T4 or N2) to the low-risk group (T1–3 N1) and so changing how long oxaliplatin should be given.

This patient had 16 nodes examined with 4 positive, a lymph node ratio of 0.25. The specimen is   adequate and his N2a labelling is good enough.

2. Adjuvant Regimen: 3 Months CAPOX versus 6 Months FOLFOX

The IDEA collaboration (Grothey et al., NEJM 2018) pooled six concurrent randomised trials, about 12,800 patients in total, comparing 3 and 6 months of oxaliplatin-based adjuvant therapy in stage III colon cancer. Overall, 3 months did not formally meet non-inferiority for 3-year disease-free survival (HR about 1.07), but the results differed by regimen and by risk group, as summarised below.

Neurotoxicity is the strongest argument for the shorter course. Grade 3 neuropathy rose about fivefold with six months of treatment. Oxaliplatin neuropathy is cumulative and often persists for years, and for a working-age man like this patient it can affect his livelihood, so the trade-off must be discussed with him directly.

Our patient is pT3 N2a, which places him in the high-risk group. The recommended approach is CAPOX, with three months framed as the minimum and extension to six months offered if he tolerates treatment, can afford it, and accepts the higher neuropathy risk after an informed discussion. Fellows should recognise that T3 N2 is the most favourable subset of the high-risk group and behaves better than T4 disease, which makes the shorter course more defensible here than in a T4 tumour.

Local calibration

The local case for CAPOX is compelling. It avoids the 46-hour infusional 5-FU, and with it the need for ambulatory pumps, central venous access, or a two-day admission every fortnight, all of which are real constraints. Three months of CAPOX means four oxaliplatin infusions compared with twelve hospital visits for six months of FOLFOX. That greatly reduces the travel burden for a patient coming from Ilesa or further afield, along with lost income and caregiver days. Generic capecitabine and oxaliplatin are off-patent.

The economic evaluation of the SCOT trial, the largest IDEA component and predominantly CAPOX, found three months to be cost-saving with equivalent quality-adjusted outcomes. In an out-of-pocket system, the cost of the full course also determines whether the patient completes treatment at all. An affordable three-month regimen that is finished is better than a six-month regimen abandoned halfway.

Capecitabine carries its own risks in our setting. Hand-foot syndrome and diarrhoea need active monitoring by phone or at clinic, with clear stop rules given to the patient, and hyperpigmentation in darker skin can hide early hand-foot syndrome. DPYD variants are a West African teaching point: the c.557A>G (Y186C) variant occurs largely in people of African ancestry and is not included in the standard four-variant European panel. Where DPYD testing is unavailable, fellows should treat cycle one as a test dose and review the patient early.

Adjuvant therapy should begin within six to eight weeks of surgery, after the post-operative CEA has been rechecked. A CEA that has not normalised suggests residual disease and should prompt restaging before treatment begins.

3. Anti-EGFR Therapy in the Adjuvant Setting, and Sidedness in Metastatic Disease

RAS wild-type status predicts anti-EGFR benefit only in metastatic disease. Two adequately powered adjuvant trials were negative. NCCTG N0147 (Alberts et al., JAMA 2012) added cetuximab to FOLFOX in KRAS wild-type stage III colon cancer and found no disease-free survival benefit, more toxicity, and a trend towards worse outcomes in older patients. PETACC-8 (Taieb et al., Lancet Oncol 2014) likewise showed no benefit. Bevacizumab failed in the same setting in NSABP C-08 and AVANT, with AVANT suggesting possible harm.

The reasons are not fully understood. Micrometastatic disease may depend on different biology from established tumours, EGFR blockade may antagonise the cell-cycle effects of oxaliplatin, and without measurable disease there is no way to select or monitor responders. The broader lesson for fellows is that a biomarker validated in one disease setting cannot be carried over to another without trial evidence.

A caecal primary is right-sided, and sidedness becomes decisive if he develops metachronous liver metastases. Retrospective analyses of CALGB/SWOG 80405 and FIRE-3 showed that anti-EGFR benefit in RAS wild-type disease is concentrated in left-sided tumours. The prospective PARADIGM trial (Watanabe et al., JAMA 2023) confirmed an overall survival benefit for panitumumab plus mFOLFOX6 over bevacizumab in left-sided RAS wild-type disease. In right-sided tumours, anti-EGFR therapy adds little or nothing in the first line, so the first-line choice for this patient would be a doublet, or FOLFOXIRI if he is fit, with bevacizumab (TRIBE data), keeping anti-EGFR therapy for later lines.

Before deciding, fellows must request BRAF V600E testing, which is enriched in right-sided tumours and carries a poor prognosis. If positive, encorafenib plus cetuximab is indicated and, on the basis of BREAKWATER, is now combined with mFOLFOX6 in the first line. HER2 amplification and KRAS G12C testing are also worth requesting where resources allow.

If the liver metastases are resectable at presentation, the standard is perioperative FOLFOX or CAPOX (EORTC 40983). Adding cetuximab in that context was harmful in the New EPOC trial, even in KRAS wild-type patients, which is a second clear example of anti-EGFR therapy failing outside palliative, measurable-disease treatment.

Local calibration

Cost will often decide whether any biologic is used at all. It is good to know the evidence-based ideal, and we should also be able to justify FOLFOX or CAPOX alone, followed by hepatobiliary surgical review, as a legitimate pathway when biologics are not accessible.

4. If the Tumour Had Been dMMR/MSI-H

Prognosis

dMMR tumours carry a more favourable prognosis in early-stage disease, most clearly in stage II. The advantage is smaller in stage III and less certain with N2 disease. In metastatic disease, dMMR was historically associated with a poorer prognosis on chemotherapy alone, but checkpoint inhibition has changed that picture.

Single-agent fluoropyrimidines

Single-agent fluoropyrimidines give no benefit in dMMR disease. In stage II, the pooled analysis by Sargent et al. (JCO 2010) suggested possible harm from 5-FU alone. dMMR stage II patients without other high-risk features therefore generally receive no adjuvant chemotherapy, and single-agent capecitabine should be avoided in dMMR stage III disease.

Checkpoint inhibition in advanced disease

Immunotherapy is now the first-line standard for metastatic dMMR colorectal cancer. KEYNOTE-177 showed that pembrolizumab roughly doubled progression-free survival compared with chemotherapy, and CheckMate 8HW showed nivolumab plus ipilimumab to be superior both to chemotherapy and to nivolumab alone.

Checkpoint inhibition in early disease

The early-stage data are now striking. In the adjuvant setting, the ATOMIC trial (Sinicrope et al., NEJM 2025) added atezolizumab to mFOLFOX6 in stage III dMMR colon cancer and roughly halved the risk of recurrence, with 3-year disease-free survival of about 86% versus 77%. This makes FOLFOX plus atezolizumab the new adjuvant standard where it is accessible. In the neoadjuvant setting, NICHE-2 showed that nivolumab plus ipilimumab in dMMR colon cancer produced major pathological responses in nearly all patients and complete pathological responses in about two-thirds. In dMMR rectal cancer, dostarlimab has produced sustained clinical complete responses that allow organ preservation.

Lynch syndrome

A dMMR result in a 54-year-old with right-sided cancer also requires thinking beyond the tumour. If MLH1/PMS2 loss is found, MLH1 promoter methylation or BRAF V600E testing should be done to separate sporadic tumours from possible Lynch syndrome, followed by germline referral and cascade testing of relatives where indicated.

Key Evidence Cited

AJCC Cancer Staging Manual, 8th edition; NCCN Guidelines: Colon Cancer.

Hohenberger W, et al. Standardized surgery for colonic cancer: complete mesocolic excision and central ligation. Colorectal Dis 2009.

Grothey A, et al. Duration of adjuvant chemotherapy for stage III colon cancer (IDEA). NEJM 2018.

André T, et al. IDEA overall survival analysis. J Clin Oncol 2020.

Iveson TJ, et al. SCOT trial. Lancet Oncol 2018 (with accompanying cost-effectiveness analysis).

Alberts SR, et al. NCCTG N0147. JAMA 2012. Taieb J, et al. PETACC-8. Lancet Oncol 2014.

Watanabe J, et al. PARADIGM. JAMA 2023. Primrose J, et al. New EPOC. Lancet Oncol 2014. Nordlinger B, et al. EORTC 40983.

Kopetz S, et al. BREAKWATER (encorafenib + cetuximab + mFOLFOX6 in BRAF V600E mCRC).

Sargent DJ, et al. MMR status and 5-FU benefit. J Clin Oncol 2010.

André T, et al. KEYNOTE-177. NEJM 2020. André T, et al. CheckMate 8HW. NEJM 2024.

Sinicrope FA, et al. ATOMIC. NEJM 2025. Chalabi M, et al. NICHE-2. NEJM 2024. Cercek A, et al. Dostarlimab in dMMR rectal cancer. NEJM 2022.