ABSTRACT
<p><b>OBJECTIVES</b>To investigate the regression pattern of mid and low rectal cancer treated with neoadjuvant chemoradiotherapy and then to provide the pathological proofs for reasonable resectional margin in rectal cancer surgery.</p><p><b>METHODS</b>Forty cases of mid and low rectal cancer patients received concurrent chemoradiotherapy and then underwent radical operation. The whole-mount serial sections of resected rectal cancer specimen were stained with cytokeratin antibody using immunohistochemical techniques to show the residual cancer cells under the mucosa. The microscopic measurement was performed to determine the reverse infiltration of cancer cells in the rectal wall and to describe the cancer cells scatter ways in the cancer mass. The Ki-67 immunohistochemical stain was also performed to show the proliferation activity of residual cancer cells after neoadjuvant chemoradiotherapy.</p><p><b>RESULTS</b>The length of specimen was shrinking continuously during the pathologic section production and the shrink rate was 18%. There were remanent cancer cells which showed positive Ki-67 expression and the chemoradiotherapy decreased the Ki-67 expression significantly. The lower edge of remaining ulcers or scars could be used as the reference point from which the cancer infiltration could be measured. According to our measurement, the average reverse infiltration of cancer cells in the whole-mount section was (6.1±4.7) mm, the deepest one was 11.0 mm in the section which could be converted into fresh bowel length of 12.98 mm. The pathology showed that the residual cancer cells scattered in the fibrous tissue of ulcers, scars and manifested a regression of spatial distribution.</p><p><b>CONCLUSIONS</b>The rectal cancers show regression in different degrees after neoadjuvant chemoradiotherapy. The residual cancer cells in the fiber tissues manifest proliferation activity. The distal end of resection should be at least 2 cm away from the lower edge of ulcers or scars of primary tumor in the rectal wall in patients after neoadjuvant chemoradiotherapy. The circumferential resection margin should include all the fibrous scar of the tumor area to ensure the remove of tumor cells completely.</p>