Tumour Staging and Grading

Tumour staging and grading are two distinct but complementary systems that together describe the nature of a malignant neoplasm and guide treatment decisions.

Staging describes the anatomical extent of disease — how far the cancer has spread. The universal framework is the TNM system, developed by Pierre Denoix in the 1940s and now maintained by the AJCC (American Joint Committee on Cancer) and UICC. T describes the primary tumour: T0 = no evidence of primary tumour, T1–T4 = increasing tumour size or local invasion. N describes regional lymph node involvement: N0 = no nodal involvement, N1–N3 = increasing number or extent of involved nodes. M describes distant metastasis: M0 = no distant metastasis, M1 = distant metastasis present.

TNM descriptors are combined into overall stage groupings I–IV. Stage I = localised disease, generally excellent prognosis. Stage II = locally advanced without nodal involvement. Stage III = regional nodal spread or significant local invasion. Stage IV = distant metastases, generally incurable with conventional therapy. Staging may be clinical (cTNM, based on examination, imaging, biopsy before definitive treatment) or pathological (pTNM, based on surgical resection specimen — generally the gold standard).

Grading (differentiation) describes how closely tumour cells resemble their normal counterpart. G1 = well-differentiated (low grade): tumour retains much of the normal tissue architecture. G2 = moderately differentiated. G3 = poorly differentiated (high grade): tumour looks very abnormal, with high mitotic rate, nuclear pleomorphism, and necrosis. G4 = undifferentiated: tumour so anaplastic it cannot be assigned to a cell lineage without immunohistochemistry. High-grade tumours tend to grow faster, metastasise earlier, and have poorer prognosis, but may be more sensitive to chemotherapy or radiotherapy.

Performance status (PS) quantifies a patient's functional capacity and ability to tolerate treatment. The ECOG/WHO scale runs from 0 (fully active, no restriction) to 5 (dead). PS 0–1 generally tolerates aggressive therapy; PS 2–3 requires careful risk-benefit assessment; PS 4 (completely disabled, confined to bed) usually limits treatment to palliative intent.

In New Zealand, the New Zealand Cancer Registry (NZCR) is a national statutory registry that records all notifiable primary cancers diagnosed since 1948. It collects TNM stage, morphology, and treatment data for audit and research purposes.

Staging investigations are selected by cancer type and clinical context. CT of chest/abdomen/pelvis is the workhorse of staging. PET-CT (using 18F-FDG) detects metabolically active metastases and is particularly useful in lymphoma, melanoma, and lung cancer. MRI is preferred for CNS staging, rectal cancer extent, and soft tissue sarcomas. Bone scan detects osteoblastic metastases (prostate, breast). Sentinel lymph node biopsy (SLNB) allows nodal staging with minimal morbidity in breast cancer and melanoma.