Rectal cancer staging post neoadjuvant therapy - how should the changes be assessed?

To compare the utility and reproducibility of tumour regression grade scoring systems during histopathological assessment of rectal cancers resected after neoadjuvant (i.e. pre-operative) chemoradiotherapy. The histopathological features of tumour regression were assessed independently in 54 rectal cancer resection specimens using three scoring systems: the Tumour Regression Grade (TRG), modified Rectal Cancer Regression Grade (m-RCRG) and RCPath Cancer Dataset (RCPath) methods. Good interobserver agreement was achieved for all three systems (kappa scores: TRG system 0.719, m-RCRG system 0.734, RCPath system 0.742). Both observers diagnosed complete tumour regression and little/no regression in 11 cases (20% of all cases) and four cases (11% of all cases), respectively. A mean of 5.6 tumour blocks/case were taken and the mean lymph node yield was 8.4/case. All three scoring systems were usable in a diagnostic setting. The clinical significance of differing degrees of tumour regression is not yet universally agreed and, with this in mind, the m-RCRG system provided the optimum balance between applicability and the accurate recording of low, moderate and high degrees of tumour regression, thus facilitating future clinicopathological studies of moderate and high degrees of tumour regression and clinical outcome.