In this study, we evaluated the impact of MLN diameter on long-term outcomes following curative colectomy for pathological stage III colon cancer by classifying 209 patients into four groups according to the largest MLN diameter. Compared to the RFS in Group A (MLN < 5 mm), that in Group D (MLN ≥ 15 mm) was significantly lower, and it was also lower in Groups C and D, but the differences were not significant. The multivariate analysis of RFS demonstrated that a maximum MLN diameter ≥ 15 mm was significantly associated with worse RFS, and the HR increased with MLN diameter. These results suggest that MLN diameter affected recurrence, and the presence of bulky MLNs was a poor prognostic factor in pathological stage III colon cancer. Two previous studies evaluated the impact of MLN size on prognosis in stage III colorectal cancer [11, 12]. One, which used a cutoff value of 5 mm to define a large MLN, reported that there were no significant differences in OS or disease-free survival (DFS) between patients with large and small MLNs [11]. The other, which used a cutoff value of 10 mm, demonstrated that patients with large MLNs had worse OS and DFS than those with small MLNs, and large MLN diameter was identified as an independent poor prognostic factor in a multivariate analysis of DFS [12]. Based on these results, patients in our study were classified into four groups to more precisely evaluate the relationship between MLN diameter and prognosis. Schrembs et al. analyzed the association between OS and the LN metastasis to LN size ratio (MSR) and demonstrated that smaller MSR values correlated with longer OS [17]; that is, a high proportion of tumor components in MLNs was associated with worse prognosis. In our study, a maximum MLN diameter ≥ 15 mm was significantly associated with worse prognosis; therefore, most of the normal lymphatic tissue might be replaced by tumor cells in bulky MLNs. Furthermore, in gastric cancer and esophageal cancer, MLN size was also reported to be a poor prognostic factor [18–20]. MLN size might reflect malignant potential in gastrointestinal cancers.
The absence of adjuvant chemotherapy was also associated with worse RFS in the multivariate analysis in this study. In pathological stage III colon cancer, adjuvant chemotherapy for 6 months is recommended by the Japanese Society for Cancer of the Colon and Rectum (JSCCR) guidelines [16]. Recent large studies reported that adjuvant chemotherapy for 3 months was noninferior to 6 months in terms of disease-free survival in low-risk stage III colon cancer, including T1, T2, T3, and N1 disease [21, 22]. However, even for this type of cancer, adjuvant chemotherapy for 6 months might be optimal if MLNs are bulky.
There are several limitations to this study. First, this was a retrospective study that was conducted at a single institution and that enrolled a relatively small number of patients. That might be why there were no significant differences in RFS between Group A (MLN < 5 mm) and Group B (MLN ≥ 5 mm and < 10 mm) or Group C (MLN ≥ 5 mm and < 10 mm). Second, in both univariate and multivariate analyses of RFS, there were no significant differences in N stage, which has been considered to be the most powerful independent prognostic factor in stage III colon cancer [23–25]. The reason for this discrepancy is unclear. The proportion of N2 cancers was significantly higher in Group D (MLN ≥ 15 mm) than in Group A (MLN < 5 mm), which might have resulted in the difference in RFS between the two groups. Therefore, multivariate analysis that included both the N stage and MLN size was performed to minimize this bias.
In conclusion, our findings indicate that a maximum MLN ≥ 15 mm was significantly associated with worse RFS in stage III colon cancer. Bulky MLNs might be a poor prognostic factor in node-positive colon cancer.