Neoadjuvant chemoradiotherapy (nCRT) is considered one of the treatment modalities of advanced rectal cancer (pT3/T4 or pN+) with the intention of downsizing and downstaging the tumour. Tumour restaging may be useful for planning the operation but tissue alteration after nCRT may disturb the accuracy of the imaging procedures.
Between July 2004 and August 2005, we analysed 28 consecutive patients (18 males, 10 females, ∼63 years) with adenocarcinoma of the middle and distal third of the rectum. High spatial resolution magnet resonance imaging (MRI) with intraluminary contrast and endorectal ultrasonography (EUS) (Olympus EU‐M30S, 12 MHz) were performed before and after nCRT as part of their preoperative staging. Radiotherapy was delivered by daily fractions of 1.8 Gy up to a total dose of 50.4 Gy. During days 1–5 and days 29–33 of radiotherapy, 5‐fluorouracil was given at a dose of 1000 mg/m2/day (maximum 1800 mg). Surgery was performed after reassessment‐staging six weeks later. There were seven abdominoperineal resections and 21 anterior resections, with a covering stoma in 17 patients.
Pathological staging was undertaken according to the TNM classification. Sections were examined meticulously to identify any residual foci of adenocarcinoma.
Regression of tumour size was described in 88.9% of cases (fig 1). Improvement of T or N classification was 58.3% for EUS and 55.6% for MRI, respectively. Complete remission was seen by the radiologist in four cases, confirmed histologically in seven.
Figure 1 Comparison of magnetic resonance imaging and histological results in T staging of tumours.
T stage and N stage were predicted correctly by MRI in 57.1% and 67.9% of cases, respectively. Nodal involvement was found in 27.8%. Overestimation of tumour size and nodal involvement in MRI was seen in 37.7% and 17.9% of cases, respectively.
Depth of extramural invasion, nodal involvement, and circumferential resection margin involvement are prognostic markers in many studies.1 Total mesorectal excision decreased local recurrence rates below 10%,2 achieving further improvement by long course nCRT. Downsizing of the tumour is reported in up to 86% of patients, with a complete response rate of 9–58%; this was 25% in our study.3 The discrepancy between clinical and pathological complete response is enormous, ranging from 25% to 77%.4 Curative R0 resection after nCRT is possible in 83–90% of patients, which was also confirmed by our results. Three and five year survival rates are up to 82% and 71%, respectively.5,6,7 The high frequency of distant metastasis (50–60%) during follow up remains a major problem of treatment.
Accuracy of EUS and MRI is reported to be 75–94% for tumour penetration and 72–83% for nodal metastases.1,8 Both methods have their limitations. EUS tends to overestimate tumour depth but is highly accurate in the assessment of early tumours. MRI is commonly used in staging of pelvic malignancies because of its fine resolution but chemoradiation may decrease its accuracy. Thickening of the rectal wall after radiation by marked fibrosis, peritumoral infiltration of inflammatory cells, and vascular proliferation may contribute to overestimation of stage assessment. Sauer et al estimated the “neoadjuvant chemoradiotherapy overtreatment rate” (of pT1 and pT2 tumours) caused by MRI overstaging to be 15–20%.8,9 In the study of Kuo et al, the overall accuracy rate in T staging with MRI after neoadjuvant chemoradiotherapy was only 47%, and was associated with overstaging in 47% and understaging in 6% of 36 patients.3 Our study reflected the same problems after nCRT.
Lymph nodes of >0.5 cm in diameter are considered malignant but size criteria are not very accurate. Overall accuracy rate for N staging with MRI was 64%, and was associated with overestimation of nodal involvement in 18% of cases.10
In conclusion, MRI after nCRT is correlated with impaired accuracy. MRI overestimation of residual tumour should be taken into consideration by the surgeon. Preoperative MRI after nCRT is not recommended for routine clinical use.
Footnotes
Conflict of interest: None declared.
References
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