Clinical Impact of Poorly Differentiated Cluster at the Invasive Front in Colorectal Cancer Invading beyond the Muscle Layer

Introduction: The clinicopathological significance of poorly differentiated cluster (PDC) at the invasive front in colorectal cancer (CRC) has been reported. We analyzed whether PDC reflects malignant findings in patients with CRC invading beyond the muscle layer. Patients and methods: Sixty-eight patients who underwent surgery between January 2015 and June 2016 for CRC invading beyond the T3 (median observation period: 32.2 months) were enrolled. The relationship between PDC and clinicopatho- logical factors was analyzed. PDC was graded based on the criteria described in a report by Ueno H et al. Results: Tumor location was at the proximal colon in 26 cases, distal colon in 34 cases, and rectum in eight cases. The number of cases with ly2,3 and v2,3 was 24 and 38, respectively. Thirty-eight cases had node positive and 11 cases had distant metastases, including 10 cases with hematogenous metastasis and four cases with peritoneal metastasis. The number of cases with stages II, III, and IV was 28, 28, and 12, respectively. The number of cases with PDC grades 1 (G1), 2 (G2), and 3 (G3) was 48, 15, and 5, respectively. A PDC G2 or G3 is a risk factor for lymph node and distant metastases. Cases with PDC G2 or G3 had significantly poor overall survival (OS) ( p < 0.0001). In cases with curability (cur) A resection for stage II or III, disease-free survival (DFS) and OS were significantly poorer in cases with PDC G2 or G3 ( p = 0.0022 and p = 0.0049, respectively). Conclusion: Analyses concerning PDC at the invasive front in cases with CRC invading beyond the muscle layer were per- formed. As the stage progresses, cases with PDC G2 and G3 increased significantly. In cases with PDC G2 and G3, the DFS and OS were significantly poorer. These results suggest that PDC is a malignant predictor in patients with CRC invading the T3 or deeper.