Table 2. The American Joint Committee on Cancer (AJCC) criteria for determining pathological response to neo-adjuvant radiotherapy in patients with rectal cancer, as determined by histological analysis after tumour resection, (Mace et al, 2015).

AJCC criteria for pathological response to neo-adjuvant radiotherapy
0	1	2	3
No viable tumour cells remaining	Single or small groups of tumour cells	Residual cancer outgrown by fibrosis	Minimal or no treatment effect

Pathological complete response (pCR) equates to a score of 0.