A significant reduction in positive circumferential margin involvement is achieved by combining a low rectal cancer MRI staging system with clinical assessment and sound patient management:experience from the MERCURY II Low Rectal Cancer Study.


Session type:

Nick Battersby1, Peter How1, Phil Quirke3, Brendan Moran1, Gina Brown2, The Mercury II study group1
1Pelican Cancer Foundation, Basingstoke, UK, 2The Royal Marsden Hospital, London, UK, 3St James' Hospital, Leeds, UK


A low rectal cancer MRI staging system was retrospectively shown to identify tumours with a threatened circumferential resection margin (CRM). This staging system was used along side clinical assessment in a prospective study in order to selectively use neoadjuvant treatment and to guide the surgical plane. The primary aim of MERCURY II was to reduce the rate of positive circumferential resection margins.


The positive CRM rate was compared between 101 patients from MERCURY I low rectal cancer subgroup and 203 patients from MERCURY II study: combined median age 68, female 112/304 (36.8%). Patient demographics, tumour stage and site, neoadjuvant treatment, operative approach, MRI and pathological findings were recorded.


Median tumour height for MERCURY I subgroup 3.8cm versus MERCURYII 4cm, (p=0.18). The circumferential resection margin was positive in 27/101 (26.8%) MERCURYI subgroup compared with 19/203 (9.4%) MERCURY II (p<0.001). Sphincter sparing surgery was performed in 31/101 (30.7%) compared with 84/203 (41.4%), for MERCURY1 subgroup and MERCURY II group respectively (p=0.79).


Combined clinical assessment with the low rectal cancer MRI staging system enabled selective treatment, with a significant overall reduction in circumferential resection margin involvement.