Imaging of rectal cancer

Magnetic resonance imaging of rectal cancer

Magnetic resonance imaging (MRI)is a useful modality for the evaluation of rectal cancer, providing superior anatomic/pathologic visualization when compared with endorectal ultrasound (EUS) and computed tomography (CT). Preoperative MRI is useful for tissue characterization and tumor staging, which determines the surgical approach and need for neoadjuvant/adjuvant therapy. Important prognostic factors include the circumferential resection margin (CRM), T and N stages, and extent of local invasion. Postoperative MRI to assess the extent of tumor recurrence enables early resection, which can greatly prolong survival. MRI criteria for local recurrence include T2 hyperintensity, early dynamic rim enhancement, and nodular morphology. Future research in MRI of rectal cancer is geared toward developing optimal imaging techniques including high-resolution MRI, whole-body scans, and parallel imaging; imaging of lymph nodes by MR lymphography; and response to therapy using diffusion/perfusion-weighted MR and functional imaging.

Current options for the management of rectal cancer

Patients diagnosed with rectal cancer should undergo locoregional staging with transrectal endoscopic ultrasound (EUS) or surface coil array MRI of the pelvis if that technique is available. Patients thought to have more than very early stage (T1 or T2) disease should undergo abdominal imaging as well by CT or MRI, and chest imaging with either CXR or preferably CT. The care of rectal cancer patients should be coordinated amongst an experienced multidisciplinary team to maximize the chance of cure and to minimize both local recurrence and complications of therapy. For patients with very early stage disease (T1N0 or T2N0), local resection with or without chemoradiation may be adequate therapy, but these patients must be selected carefully and should be without any poor prognostic factors. For the majority of patients with T3N0 or greater rectal cancer, standard therapy consists of neoadjuvant continuous 5-FU and radiation followed by surgery and further chemotherapy (either with 5-FU, capecitabine, or FOLFOX). The use of capecitabine, irinotecan, and oxaliplatin during radiotherapy shows promise, but remains investigational pending results of phase III studies. Neoadjuvant therapy is preferred because it decreases local recurrence and appears to result in improved postoperative bowel function in comparison with postoperative therapy. Select patients with high (>10 cm from the anal verge) uT3N0 tumors may be at sufficiently low risk of local recurrence to justify omission of radiotherapy. Patients who experience pathologic complete response to radiotherapy should still receive postoperative adjuvant chemotherapy to reduce systemic recurrence risk until data demonstrate that this is not necessary. Patients with stage IV rectal cancer may still require local therapy with radiation, surgery, or both; however, care should be taken in these patients that chemotherapy is not excessively delayed as this is the one modality in this case that can result in improved survival.

cT3N0 rectal cancer: potential overtreatment with preoperative chemoradiotherapy is warranted

PURPOSE

Although combined-modality therapy (CMT) is the preferred treatment for T3 and/or lymph node (LN)-positive rectal cancer, the German rectal cancer study published in 2004 demonstrated that 18% of patients deemed suitable for preoperative CMT by endorectal ultrasound (ERUS) may be overstaged. Because data also suggest that LN-negative rectal cancer after total mesorectal excision may not require radiotherapy, it is reasonable to consider omitting radiotherapy for the cT3N0 subset. We therefore determined the accuracy of pre-CMT ERUS or magnetic resonance imaging (MRI) staging, to explore the validity of a nonpreoperative CMT approach for cT3N0 disease.

PATIENTS AND METHODS

One hundred eighty-eight ERUS-/MRI-staged T3N0 rectal cancer patients received preoperative CMT (fluorouracil based and 45-50.4 Gy) followed by radical resection. Rates of pathologic complete response (pCR) and mesorectal LN involvement were determined.

RESULTS

Tumors were located a median of 5 cm from the anal verge. Sphincter-preserving surgery was performed in 143 patients (76%). Overall pCR was 20%, and 41 patients (22%) had pathologically positive mesorectal LNs. The incidence of positive LNs significantly increased with T stage: ypT0, 3%; ypT1, 7%; ypT2, 20%; ypT3-4, 36% (P = .001).

CONCLUSION

The accuracy of preoperative ERUS/MRI for staging mid to distal cT3N0 rectal cancer is limited because 22% of patients have undetected mesorectal LN involvement despite CMT. Therefore, ERUS-/MRI-staged T3N0 rectal cancer patients should continue to receive preoperative CMT. Although 18% may be overstaged and therefore overtreated, our data suggest that an even larger number would be understaged and require postoperative CMT, which is associated with significantly inferior local control, higher toxicity, and worse functional outcome.

Increased detection rate and potential prognostic impact of disseminated tumor cells in patients undergoing endorectal ultrasound for rectal cancer

BACKGROUND

Hematogenous tumor-cell dissemination during diagnostic and therapeutic procedures in patients with colorectal cancer has been demonstrated.

OBJECTIVE

The aim of this study was to investigate the extent of disseminated tumor cells in blood samples of rectal cancer patients after endorectal ultrasound and to determine its prognostic relevance.

MATERIALS AND METHODS

Peripheral venous blood samples from 45 patients with rectal cancer were taken before and after endorectal ultrasound. Blood samples were examined using a reverse transcriptase-polymerase chain reaction (RT-PCR) assay to amplify cytokeratin 20 transcripts. Overall survival of the patients was calculated by the Kaplan-Meier method.

RESULTS

Disseminated tumor cells were detected in peripheral blood samples of 17 of 45 (38%) patients before and after endorectal ultrasound. Circulating tumor cells were found in 11 of 45 (24%) patients only after endorectal ultrasound (p=0.006). There was a clear trend toward a worse prognosis in patients with tumor cells in blood samples after endorectal ultrasound, but this difference was not statistically significant.

CONCLUSION

This study demonstrates significantly increased hematogenous tumor-cell dissemination after endorectal ultrasound in rectal cancer patients. Patients with tumor cells in blood samples after endorectal ultrasound tend to have a worse prognosis. The potential prognostic impact of this finding is presently unclear and has to be further validated in larger clinical trials.