Accuracy of endorectal ultrasound for measurement of the closest predicted radial mesorectal margin for rectal cancer.

BACKGROUND: At present, pelvic phased array-coil MR is used as the validated imaging modality for measurement of the closest predicted radial mesorectal margin for rectal cancer. Endorectal ultrasound is also used to assess the clinical stage of the cancer that will determine the recommendation for neoadjuvant chemoradiation, but it has not been used to assess the closest predicted radial margin. OBJECTIVE: We propose to assess endorectal ultrasound identification of mesorectal margins and the measurement of the closest predicted radial tumor-mesorectal margin. PATIENTS AND METHODS: Patients included were those having MRI and endorectal ultrasound for evaluation of primary rectal cancer in 2010 at a tertiary cancer referral colorectal clinic. Clinical data, MRI, and endorectal ultrasound images were assessed. Two independent retrospective measurements of mesorectal dimensions were correlated to evaluate the reproducibility of identifying mesorectal margins. MRI and endorectal ultrasound images were compared for independent measurements of mesorectal dimensions and of the closest predicted radial mesorectal margin. MRI and endorectal ultrasound determination of margin involvement were assessed for agreement. RESULTS: Fifty-two patients were studied with an average rectal cancer distance to the anal verge of 6.8 cm. Interobserver correlation coefficients of endorectal ultrasound mesorectal dimensions ranged from 0.47 to 0.53 (p < 0.01). MR and endorectal ultrasound measurements of the closest predicted radial mesorectal margin were correlated r = 0.56 (p < 0.0001). MR and endorectal ultrasound determination of margin involvement agreed in 81% of cases. CONCLUSION: Endorectal ultrasound has substantial agreement with MR to measure the closest predicted radial tumor-mesorectal margin. Correlations between observers and modalities for identification of mesorectal dimensions are modest. Further assessment is indicated to confirm endorectal ultrasound mesorectal measurements in a larger sample and to understand the advantages and disadvantages relative to MR.

A metastatic colon cancer model using nonoperative transanal rectal injection.

BACKGROUND: This study aimed to develop a noninvasive orthotopic model for metastasis of colon and rectal cancer using a transanal approach. Currently, the most accurate orthotopic representation of metastatic human colon cancer is via a cecal injection. The transanal model allows for further examination of systemic immune responses, tumor take, and onset of metastasis without prior surgical intervention. METHODS: For this study, 60 Balb/c mice were anesthetized and subjected to gentle anal dilation using blunt-tipped forceps at the anal opening. Murine colon cancer parental CT26 or luciferase-labeled CT26 (CT26-luc) cells were injected submucosally into the distal posterior rectum (30 CT26 and 30 CT26 injections) at concentrations of 2.5 x 10(4), 1 x 10(5), and 1 x 10(6) in a volume of 50 microl. Tumor growth and metastatic development was monitored at 5-day intervals for 50 days. All the remaining mice were killed on postinjection day 50. RESULTS: The optimal concentration for metastasis and survival of the mice was 2.5 x 10(4) cells. Higher concentrations of cells yielded higher mortality but did not result in metastasis. The overall success of tumor growth in both experiments using the transanal rectal injection was 65%. Histology showed that all tumors were poorly differentiated adenocarcinomas. Two mice (3.3%) from the 2.5 x 10(4) CT26-luc group showed metastatic colonic adenocarcinoma to the liver on postinjection day 50. CONCLUSION: Transanal rectal injection of colon cancer cells offers a nonoperative orthotopic murine model for colon cancer that may lead to the development of metastasis. By using an orthotopic model, more aspects of metastatic colon cancer can be evaluated without the influence of a previous abdominal incision. These results warrant more investigation.