Abstract: Background and purpose: Histological grading based on the degree of differentiation has limitations in evaluating the biological behavior of colorectal cancer. Finding more morphological indicators will provide more evidence for the prognosis and stratified management of colorectal cancer. This study aimed to investigate the relationship between poorly differentiated clusters (PDC) and clinicopathological parameters in colorectal adenocarcinoma and its significance. Methods: Data of 101 patients with colorectal adenocarcinoma who underwent radical surgical resection in Zhuhai Hospital of Guangdong Provincial Hospital of Traditional Chinese Medicine from January 2019 to October 2020 were collected. Among them, there were 54 males and 47 females, ranging in age from 29 to 86 years with median age of 62 years. Tumor size ranged from 1.5 to 9.0 cm (mean 4.5 cm). There were 42 cases of left colon cancer, 21 cases of right colon cancer and 38 cases of rectal cancer. The number of PDC of colorectal adenocarcinoma in H-E section was observed under light microscope and graded, and the relationship between PDC grade and other clinicopathological parameters of colorectal adenocarcinoma was analyzed. Results: Among 101 cases of colorectal adenocarcinoma, 42 cases (41.6%) were G1 grade, 29 cases (28.7%) were G2 grade, and 30 cases (29.7%) were G3 grade. In colorectal adenocarcinoma, PDC was positively correlated with histological grade, invasion depth, lymph node metastasis, lymphovascular invasion, nerve invasion, distant metastasis stage and tumor budding (TB) (P ＜ 0.05), but not with patient age, gender, tumor site or tumor size (P ＞ 0.05). Conclusion: PDC is closely related to the invasive biological behavior of colorectal adenocarcinoma. PDC is likely to be a more effective prognostic marker than traditional histological grading after TB. Identification and evaluation of PDC grading in colorectal adenocarcinoma can better predict the biological behavior of colorectal adenocarcinoma, and thus more accurately guide the treatment and prognosis evaluation of colorectal cancer.

Key words: Colorectal adenocarcinoma, Poorly differentiated clusters, Tumor budding