Reply to: Does MRI Restaging of Rectal Cancer After Chemoradiotherapy Actually Permit a Change in Surgical Management?
We read with interest the letter by Smith et al1 about our research validating MRI assessment of the low rectal plane of surgery for rectal cancer. The letter focuses on MRI assessment of response after chemoradiotherapy (CRT), which was one aspect of the article.
Although we agree that this is a subject of extreme importance, one should not lose sight of a key message of the MERCURY II study: when staging and surgery are optimal, and the MRI low rectal plane (mrLRP) is “safe,” it is often possible to avoid CRT. Overall 39% (109/279) of study participants proceeded to surgery without the morbidity that is associated with CRT. In addition, pathological circumferential resection margin (pCRM) involvement was 1.6% (1/62) when the mrLRP was “safe” and there were no other adverse radiological features.1 However, once the decision to use CRT is made, we strongly encourage clinicians to restage patients, and the majority of the clinicians in MERCURY II did so (91%, 154/170).
Smith et al interpret our data to suggest MRI is of limited clinical utility for restaging patients after CRT. On the contrary, modified management in terms of deferral of surgery and a change in operative approach for good and poor responders indicate the need, if not mandatory requirement, for post-CRT reassessment.
The most profound demonstration of the benefit from posttreatment MRI restaging is provided by 5 patients who were excluded from analysis because of clinical and radiological evidence of a complete response. Clinicians discussed posttreatment MRI results with these patients and the concordant decision was to “defer surgery” through a non-operative management approach.2 Despite intensive follow up these 5 patients have avoided surgery and remain recurrence free. Such patients are likely to receive relative gains in quality of life by avoiding total mesorectal excision (TME) surgery, a stoma and by reducing their degree of postoperative bowel dysfunction. Moreover, the cost of intensified nonoperative follow up is more than offset by avoiding the total costs from TME surgery. The limited long-term follow-up data that is available suggest that this strategy is feasible and safe,3 however we accept that currently it should only be performed in the context of a clinical trial.
Secondly, Thirty-three patients (29.2%, 33/113) demonstrated regression to a “safe” low rectal plane (ymrLRP). None of these patients had pCRM involvement and the plane of surgery became less radical in 8 (24.2%) patients. We agree that almost three-quarters (80/113) of “good responders” may not have gained optimal benefit from what appeared to be a complete or “near complete” radiological response. We cannot be certain whether the unwillingness to change strategy reflects the patients’ fear of taking a less radical treatment approach or if this indicates the clinicians concern not to challenge current consensus.4 Nonetheless, this does not suggest that the posttreatment MRI is of limited clinical utility, instead it highlights that we need to make better use of the information that this reimaging provides.
The final group to benefit from restaging was the 6% (9/154) of patients who progressed on treatment from a “safe” mrLRP to an “unsafe” ymrLRP. This led to a change in strategy and several patients underwent exenteration or more radical surgery than initially planned. It is also noteworthy that the nonrestaged patients had higher pCRM involvement than “poor responders,” which may represent missed opportunities to preoperatively identify disease progression.
As clarification for Smith et al, radiologically and pathologically, we defined a clear circumferential resection margin (CRM) as tumor >1 mm from mesorectal fascia without a breach in the intersphincteric plane and we defined a “good response” by the composite measure of a “safe” ymrLRP and mrTRG1-2.