Locally advanced rectal cancer: histopathological correlation and predictive accuracy of serial MRI after neoadjuvant chemotherapy

Abstract

The accuracy of MRI after long-course chemoradiotherapy (CRT) in locally advanced rectal cancer (LARC) has been questioned. We have evaluated our experience of sequential MRI to assess pre-operative downstaging with histopathology correlation. 17 patients with LARC had three MRI scans: MRI 1, before treatment; MRI 2, 6 weeks post-CRT; and MRI 3, pre-operatively. MRI T and N staging were reported, with T3 subdivided into T3a (<5 mm through wall), T3b (1-5 mm), T3c (5-15 mm) and T3d (>15 mm). The maximal wall measurements and a prediction of vascular involvement were also correlated with histopathology. Histopathological agreement with MRI 3 was high: T 82%; N 88% and vascular 73%. Statistically significant (p<0.01) T downstaging was shown in MRI 2 and MRI 3 groups. In the 6 weeks post-CRT scan, T downstaging occurred in 6% of patients, with a further 29.4% showing T3c to T3b downsizing. 41% showed N stage improvement. In the third MRI group pre-surgery, 41.2% showed an MRI T stage improvement, with a further T3 downsizing in 17.6% of patients. 50% of these responders had shown no T stage improvement on their second scan. The sequential scans also showed significant reduction in wall thickness (p<0.01). In conclusion, the pre-operative MRI showed ongoing response to CRT up to 12 weeks post-CRT, which has important clinical implications regarding the most appropriate time to operate. Improved agreement between MRI 3 and histopathology compared with previous studies including only one post-treatment MRI was also demonstrated.

Laparoscopic total mesorectal excision following long course chemoradiotherapy for locally advanced rectal cancer

“…The authors have earlier presented data documenting the ongoing response to RT as seen on serial MRI [33] and higher correlation with final histology [34]. There is a potential that the use of serial MRI scans may prove to be very useful in determining the optimal timing of surgery [33,34]. We have found a close correlation between the final pathology and the final, preoperative MRI scan.…”

“…In our institution, following multidisciplinary discussion, a third MRI has been performed in a subset of patients with locally advanced rectal cancer who had undergone CRT and had appeared to show little or no response on their follow-up MRI. The authors have earlier presented data documenting the ongoing response to RT as seen on serial MRI [33] and higher correlation with final histology [34]. There is a potential that the use of serial MRI scans may prove to be very useful in determining the optimal timing of surgery [33,34].…”

Timing of Surgery Following Preoperative Therapy in Rectal Cancer: The Need for a Prospective Randomized Trial?

“…Therefore, our data provide further support to the recent observations that have indicated a trend toward continued tumor regression when surgery is delayed beyond 6 to 8 weeks after the completion of radiotherapy. 5,19 Concerning perioperative morbidity, our results showed that anastomotic leaks were observed in each of the groups with equal frequency, and wound infections were equally distributed between the 3 groups, as well. However, a nonsignificant increase in blood loss requiring blood transfusion was noted in the delayed group.…”

“…5,6 An audit of 189 patients found that shorter intervals independently predicted anastomotic leak rates and perineal wound complications. 6 In a retrospective analysis Habr-gama et al 7 showed that there was no difference in overall survival and disease-free survival in 250 patients who underwent surgery before 12 weeks and after 12 weeks, suggesting that the deferral of surgery may be safe.…”

Waiting Time following Neoadjuvant Chemoradiotherapy for Rectal Cancer: Does It Really Matter

“…De Campos-Lobato et al [1] showed that waiting for more than 8 weeks between completion of CRT and surgery was associated with significant improvement in pathological complete response (pCR) rate (30.8 vs. 16.5%, p = 0.03) and decreased the 3-year local recurrence rate (1.2 vs. 10.5%, p = 0.04). Other studies have indicated downstaging and better surgical outcomes with a delay of more than 8 weeks [11,12]. This published evidence suggests that there is continuous local downstaging beyond 8 weeks in many patients.…”