Patient characteristics

Totally, 426 patients were enrolled, including 53.2% males (227/426), and the mean age was 64 years old (range: 31–93 years old). The mean diameter of primary tumor lesion was 4.7 cm (range: 0.9–9.0 cm). The primary tumor sites were the left colon (n = 148), the right colon (n = 109), and the rectum (n = 169). There were 211 patients in the N + group and 215 patients in the N- group (Fig. 3).

Fig. 3

The flow diagram for this study. CRC, colorectal cancer; LN, lymph node; LN-,No lymph node metastasis;LN + ,Lymph node metastasis; pTB,Tumor budding in the invasive front of primary lesions; pPDC, Poorly differentiated clusters in the invasive front of primary lesions; nTB, Tumor budding in metastatic lesion of lymph node; nPDC, Poorly differentiated clusters in metastatic lesion of lymph node

Differential and correlation analysis of TB and PDC in primary tumors between the N- and N + groups

The proportions of TB1, TB2 and TB3 were 78.52%, 42.17% and 32.47% in the N- group while 21.48%, 57.83% and 67.53% in the N + group, and the differences between the two groups were statistically significant (Z = 8.24, P < 0.001). Similarly, the proportions of PDC1, PDC2 and PDC3 in the two groups were 83.76%, 50.83%, 29.63% and 16.24%, 49.17%, 70.37%, respectively, and the differences also exhibited statistical significance (Z = 9.03, P < 0.001) (Table 1).

Table 1 Difference and correlation analysis between N- /N + groups and TB/PDC grades in primary lesions of colorectal adenocarcinoma

Correlation analysis results demonstrated that TB in primary lesion was significantly correlated with the occurrence of LN metastasis (r = 0.38, P < 0.001). Comparatively, the odds ratio (OR) for TB2/3 was 6.68-fold higher than that for TB1 in LN metastasis in N + patients, suggesting a positive correlation between the TB in primary lesion and occurrence of LN metastasis. In addition, positive association was also demonstrated between the PDC in primary lesion and the occurrence of LN metastasis (r = 0.41, P < 0.001), and the OR for PDC2/3 in LN metastasis was 8.46-fold higher than that for PDC1 (Table 1).

Differential and correlation analysis of TB and PDC in primary tumors between different LN + subgroups

Both TB (Z = 14.52, P = 0.006) and PDC (Z = 21.92, P < 0.001) demonstrated statistically significant differences between different N + subgroups. Additionally, TB (r = 0.14, P = 0.017) and PDC (r = 0.20, P = 0.011) also had significant correlations with different N + subgroups, respectively. Comparatively, the OR for TB2/3 and PDC2/3 in pN2 (2a, 2b) was 3.08-fold and 2.86-fold higher than that for TB1 and PDC1 (Table 2), respectively, suggesting positive correlations between TB/PDC and the number of LN metastases.

Table 2 Analysis of the difference and correlation between lymph node staging and TB, PDC grading in primary lesionsDifferential and correlation analysis of TB and PDC in primary tumors and LN metastases

The proportions of pTB1, 2 and 3 in primary tumors were 34.78%, 31.88%, 33.33%; 13.04%, 32.61%, 54.35%; 2.08%, 11.46%, 86.46%, corresponding to nTB1, 2 and 3 in LN metastases, respectively. The differences between groups had statistical significance (Z = 54.18, P < 0.001) (Table 3). The proportions of PDC1, 2 and 3 in primary tumors were 24.19%, 48.39%, 27.42%; 3.77%, 41.51%, 54.72%; 1.05%, 7.37%, 91.58%, corresponding to nPDC1, 2 and 3 in LN metastases, respectively, and the differences between groups had statistical significance (Z = 70.61, P < 0.001) (Table 4).

Table 3 The difference and correlation analysis of TB grade between LN metastatic lesion and primary lesionTable 4 The difference and correlation analysis of PDC grade between LN metastatic lesion and primary lesion

The result of correlation analysis showed a moderate correlation between the primary tumors and LN metastases in terms of TB (r = 0.47, P < 0.001) (Table 3) and PDC (r = 0.54, P < 0.001) (Table 4).