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ABSTRACT & COMMENTARY
Synopsis: Local recurrence after rectal cancer surgery remains a problem. It is probable that tumor resection margins are predictive of local control, but the preoperative assessment to define those likely to have adequate margins has not been established. In the current report, magnetic resonance imaging (MRI) with phased-array coil was used preoperatively to define stage and predict tumor margins in 76 patients with rectal cancer treated at a single institution. Although the MRI was not highly accurate with regard to staging, it was in predicting the surgical margins. Beets-Tan and colleagues suggest that this information may have clinical importance in determining which patients are at risk for local recurrence and who might, therefore, benefit from preoperative radiation therapy.
Source: Beets-Tan RG, et al. Lancet. 2001;357:
Modern mri techniques with endorectal and phased-array coils offer spatial-resolution advantages when compared to standard MRI, computerized tomography (CT), or ultrasonograpy (US). Beets-Tan and colleagues from the University Hospital of Maastricht, Netherlands used this technique in the preoperative assessment of 76 patients with rectal cancer. Two observers independently scored, on 2 occasions, the tumor stage and measured distance to the mesorectal fascia. Their findings were compared to histological measurements of the resected tumor specimens.
There was some discrepancy between the 2 reviewers, particularly with regard to tumor stage. For the first, the MRI-determined stage agreed with the histological stage in 63 (83%) of the 76 patients, whereas for the second the agreement was 67%. However, the results with regard to tumor margin were more favorable and reliable. In all 12 patients with an obvious T4 lesion, a margin of 0 mm was correctly predicted. Of the 29 patients with a pathological margin of greater than 10 mm, a distance of at least 10 mm was predicted in 28 by observer 1, and 27 by observer 2. For the remaining 35 patients, a regression curve revealed that the clinically important 1 mm tumor-free margin was confidently predicted when the measured distance (by MRI) of tumor from the mesorectal fascia was more than 5 mm.
Beets-Tan et al conclude that a high level of accuracy with regard to circumferential resection margin is afforded by this MRI technique (with a phased-array coil) and that this provides important clinical information. They suggest that such a preoperative assessment may assist in determining which patients would benefit from neoadjuvant radiation (plus chemotherapy) and defining optimal surgical approaches.
COMMENT by William B. Ershler, MD
Local recurrence after curative-intention surgery for rectal cancer varies from 3-32%1 and it is generally believed that extension of the tumor to, or beyond the mesorectal fascia with residual malignant cells after total mesorectal excision (TME) is the primary factor affecting local recurrence.2,3 Preoperative radiotherapy has been shown to reduce local recurrence rates and improve survival,4 and this approach is commonly used. Alternatively, postoperative radiation therapy and chemotherapy have been frequently used in patients with T3 and/or N1 lesions.
However, even without radiation therapy, overall recurrence rates for T2 or T3 lesions are estimated to be 10% or less after total mesorectal resection if there is a tumor-free resection margin of more than 1 mm.5,6 Thus, if a preoperative imaging technique is developed which accurately defines anticipated resection margins, it may identify individuals who would not require perioperative radiation.
Before such an approach becomes commonly used, however, it is clear that additional research is needed. Even at the university hospital reporting this study and committed to this technique, there was considerable inter-observer variability. Certainly, standardized approaches and interpreter training will be necessary if these exciting findings are confirmed.
If it is true that resection margins are, as expected, a critical factor predicting local recurrence, future trials are necessary to determine if preoperative radiation to those with high-risk (as determined by MRI) benefit in terms of local recurrence or enhanced survival. Furthermore, the cost effectiveness of such an approach will need investigation before the technique can be adapted on a large scale. From a financial perspective, this analysis might indicate that preoperative MRI is cost effective if a substantial percent of rectal cancer patients are spared radiation therapy or unnecessarily aggressive surgery as a result.
1. Sagar PM, et al. Br J Surg. 1996;83:293-304.
2. Adam IJ, et al. Lancet. 1994;344:707-711.
3. Quirke P, et al. Lancet. 1986;2:996-999.
4. Swedish Rectal Cancer Trial Investigators. N Engl J Med. 1997;336:980-987.
5. MacFarlane JK, et al. Lancet. 1993;341:457-460.
6. Havenga K, et al. Eur J Surg Oncol. 1999;25:368-374.