AIM:To assess the microscopic spread of low rectal cancerin mesorectum regions to provide pathological evidencefor the necessity of total mesorectal excision(TME).METHODS:A total of 62 patients with low rectal cancerunderwent low anterior resection and TME,surgical specimenswere sliced transversely on the serial embedded blocks at2.5 mm interval,and stained with hematoxylin and eosin(HE).The mesorectum on whole-mount sections was divided intothree regions:outer region of mesorectum(ORM),middleregion of mesorectum(MRM)and inner region of mesorectum(IRM).Microscopic metastatic foci were investigatedmicroscopically on the sections for the metastatic mesorectalregions,frequency,types,involvement of lymphatic vesselsand correlation with the original rectal cancer.RESULTS:Microscopic spread of the tumor in mesorectumand ORM was observed in 38.7%(24/62)and 25.8%(16/62)of the patients,respectively.Circumferential resectionmargin(CRM)with involvement of microscopic metastaticfoci occurred in 6.5%(4/62)of the patients,and distalmesorectum(DMR)involved was 6.5%(4/62)with thespread extent within 3 cm of low board of the main lesions.Most(20/24)of the patients with microscopic metastasisin mesorectum were in Dukes C stage.CONCLUSION:Results of the present study support thatcomplete excision of the mesorectum without destructionof the ORM is essential for surgical management of lowrectal cancer,an optimal DMR clearance resection marginshould be no less than 4 cm,further pathologic assessmentof the regions in extramesorectum in the pelvis is needed. AIM: To assess the microscopic spread of low rectal cancer in mesorectum regions to provide pathological evidence for the necessity of total mesorectal excision (TME). METHODS: A total of 62 patients with low rectal cancer underwent low anterior resection and TME, surgical specimens were sliced ​​transversely on the serial embedded blocks at 2.5 mm interval, and stained with hematoxylin and eosin (HE). The mesorectum on whole-mount sections was divided intothree regions: outer region of mesorectum (ORM), middleregion of mesorectum (MRM) and inner region of mesorectum (IRM). Microscopic metastatic foci were investigated microscopically on the sections for the metastatic mesorectal lesions, frequency, types, involvement of lymphatic vessels and correlation with the original rectal cancer .RESULTS: Microscopic spread of the tumor in mesorectumand ORM was observed in 38.7% (24 / 62) and 25.8% (16/62) of the patients, respectively. Circulation resection margin (CRM) with involvement of microscopic metastatic foci occurred in 6. 5% (4/62) of the patients, and distal mesorectum (DMR) involved was 6.5% (4/62) with the extent of coverage within 3 cm of low board of the main lesions. Most (20/24) of the patients with microscopic metastasisin mesorectum were in Dukes C stage. CONCLUSION: Results of the present study support that completely excision of the mesorectum without destruction of the ORM is essential for surgical management of lowrectal cancer, an optimal DMR clearance resection marginshould be no less than 4 cm, further pathologic assessment of the regions in extramesorectum in the pelvis is needed.