What "stage III" means
The stage describes how far the tumour has spread. In stage III the cancer has grown beyond the bowel wall and reached nearby lymph nodes, but there are no metastases in other organs (that would be stage IV). Within stage III there are subgroups (IIIA, IIIB, IIIC) according to how many nodes are involved and how deeply the tumour has grown into the wall; your pathology report shows this as "pT… pN…".
An example: "pT3 pN1b" means the tumour grows through the muscle layer of the colon (T3) and 2-3 of the nodes examined were involved (N1b).
Standard treatment
- Surgery: the segment of colon with the tumour and the nearby lymph nodes are removed. For proper staging, at least 12 nodes should be examined.
- Adjuvant chemotherapy (after surgery), ideally starting within 6-8 weeks. Its aim is to eliminate any remaining cells and reduce the risk of relapse. The usual combinations are CAPOX (capecitabine tablets + oxaliplatin) or FOLFOX (5-fluorouracil + leucovorin + oxaliplatin).
3 or 6 months? Since the IDEA study (2018), in low-risk stage III (T1-3 and N1) three months of CAPOX are as effective as six, with far less neuropathy. In high-risk disease (T4 or N2) six months are usually recommended. Ask which of the two groups you are in.
In rectal cancer the order is different: radiotherapy and/or chemotherapy are usually given before surgery (neoadjuvant treatment or "total neoadjuvant therapy").
Tests you should have before deciding
- MSI/MMR status (microsatellite instability): done on the tumour tissue. If it is MSI-H/dMMR, the prognosis is better, fluoropyrimidine-only chemotherapy adds little, and there are trials of immunotherapy even in early stages. It also means Lynch syndrome must be ruled out.
- Baseline CEA and a chest-abdomen-pelvis CT to confirm there are no metastases.
- More and more hospitals offer a circulating tumour DNA (ctDNA) test after surgery, still mostly within trials: it helps estimate the risk of relapse.
Prognosis
With surgery and chemotherapy, most people with stage III disease are cured. The figures vary a lot by subgroup: in population registries, 5-year survival for "regional" disease (nodes involved) averages around 70-75 %, higher in IIIA and lower in IIIC. These are averages across thousands of people: your own case depends on your age, general health, MSI status, the quality of the surgery and completing treatment.
After treatment
Follow-up lasts at least 5 years: a visit with CEA every 3-6 months, a yearly CT in the first years and a colonoscopy at one year and then every 3-5 years. Most relapses, if they happen, appear in the first two years; that is why monitoring is closest at the start.
What to ask at your appointment
- What is my exact sub-stage (T and N), and how many nodes were examined?
- Is my tumour MSI-H/dMMR? Has Lynch syndrome been tested for?
- Should I have 3 or 6 months of chemotherapy, and with which regimen?
- Is there a clinical trial for my situation (for example, ctDNA or immunotherapy)?
- When do we start? Which side effects should I watch for, and whom do I call?