MRI in predicting curative resection of rectal cancer

Editor—Tumour shrinkage by preoperative chemoradiotherapy is now an everyday reality, and pathological complete responses are not uncommon.¹ A “new dilemma” is posed by the apparent complete disappearance of cancer on magnetic resonance imaging, and often clinically, after chemoradiotherapy. A delay of six to 10 weeks is usual before operating—a time perceived as a “window of opportunity,” as regrowth in the irradiated area is believed inevitable.

This concept has been challenged by a series by Habr-Gama et al.² Altogether 360 patients with T3 and T4 rectal cancer (or T2 when considered for abdominoperineal resection) were treated with preoperative chemoradiotherapy.³ Ninety nine patients (28%) classified as clinical complete responders at eight weeks after completion of chemoradiotherapy were managed by surveillance alone. Only 2% in this observation group have died of cancer in a follow-up extending for up to 10 years, whereas local recurrence occurred in just five patients, all amenable to successful salvage surgery.

We propose to open accrual into a pilot study of observation for complete responders, as assessed on magnetic resonance imaging at four weeks after completing chemoradiotherapy. This will be administered at the Pelican Centre and largely delivered at the Royal Marsden Hospital. Magnetic resonance imaging, whose excellence in accurately predicting surgical mesorectal margins has been shown by the MERCURY group,⁴,⁵ will be central to this study's intensive follow-up, in addition to regular clinical and sigmoidoscopic assessment.

Specialised primary surgery, backed by magnetic resonance imaging based selection for preoperative chemoradiotherapy, will continue to be the cornerstone of management. Nevertheless, our fundamental understanding of modern cancer treatment for all solid tumours demands that this group of complete responders be properly investigated. Furthermore, if the experience of Habr-Gama et al is confirmed, several hundred patients with rectal cancer in the United Kingdom each year may one day be spared the necessity for major surgery.