The R classification (residual tumour) after surgical resection has prognostic significance. Which of the following correctly defines R1 resection?

• A No residual tumour; negative microscopic margins (≥1 mm clearance)
• B Macroscopic residual tumour visible to the surgeon at the operative site
• C Tumour extending beyond the surgical field without margin involvement
• D Microscopic residual tumour at the resection margin (positive margin on histopathology) ✓

Explanation

R classification: R0 — no residual tumour, microscopically clear margins; R1 — microscopic residual tumour (positive margin on histological examination — tumour cells at the inked margin); R2 — macroscopic residual tumour visible to the surgeon (incompletely excised gross disease). R1 resection is associated with significantly worse local recurrence and survival across most solid tumours. The definition of 'positive' margin varies by tumour type (0 mm for some, <1 mm for others).

Reference: Bailey & Love's Short Practice of Surgery, 27th ed.

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