Patients’ clinical and pathological characteristics
More than half of the patients were men (55.6%), and the patients’ average age at the time of surgery was 70.5 years (range 29 - 92 years). The median follow-up period of the entire patient group was 60 months. The baseline clinicopathological characteristics of the 169 patients are shown in Table 1. In this study, 32 patients (18.9%) had MY (MY group), and 137 (71.1%) patients did not (NMY group). The regimens of adjuvant chemotherapy in MY group and NMY group are shown in Table 2. Patients who received completely AC was 22 (13.6%) cases (MY; 6 patients, NMY; 16 patients). Three of 22 patients who were withdrawal due to have a drug allergy, were excluded from AC group. These patients received 2-4 cycles intravenous or oral AC. Twenty-three of 169 patients developed postoperative relapses, including lung metastasis (6 patients), liver metastasis (8 patients), peritoneal dissemination (5 patients), metastasis to the para-aortic lymph nodes (3 patients), and local relapse (1 patient). Seventeen patients (17/169, 10.1%) died of any causes within the follow-up period, and seven of these patients (7/17, 41.2%) died of causes other than primary colon cancer.
Relationships between myxoid stroma and clinicopathological characteristics
The relationships between MY and clinicopathological characteristics are shown in Table 3. TB and postoperative relapse were significantly more frequent in the MY group than in the NMY group (p<0.001 and p<0.001, respectively). None of the other clinicopathological characteristics was associated with the presence of MY.
Survival analyses of relapse-free survival and overall survival
The 5-year RFS and OS rates were 87% and 89.6%, respectively, for the entire group of patients in this study. The MY group had significantly lower RFS and OS rate than the NMY group (Figs. 2, 3). The 5-year RFS rates in MY group and NMY group were 52.1% and 94.6% (p<0.0001), and the 5-year OS rates in MY group and NMY group were 74.6% and 93.3% (p=0.001). Regarding patients who did not receive AC, the MY group had significantly lower RFS and OS rates than the NMY group (p<0.001 and p=0.028, respectively Figs. 4, 5).
Univariate- and multivariate analyses to identify characteristics related to relapse-free survival and overall survival
Univariate and multivariate analyses to identify characteristics significantly related to RFS and OS rates were performed using Cox proportional hazard models (Table 4). On univariate analyses for RFS rate, TB, surgical margin, and the presence of MY were significantly associated with lower RFS rate (p=<0.001, 0.038 and p=<0.001, respectively). Regarding the OS rate, the serum CA19-9 level, deep tumor penetration, TB, positive surgical margin, and the presence of MY were significantly associated with lower OS rate in univariate analysis (p=0.026, p=0.011, p=0.001, p=0.014 and p=0.003).
On multivariate analysis for RFS and OS rates, the presence of MY and TB were significant risk factors for RFS rate (MY: HR, 6.80; 95% CI, 2.579-17.911; p<0.001, TB: HR, 4.11; 95% CI, 1.301-13.002; p=0.02), and only TB was a significant risk factor for OS rate (HR, 1.94; 95% CI, 1.020-3.668; p=0.043).
Combination of myxoid stroma and tumor budding for postoperative relapse and survival
The relationships of the combination of MY and TB with 5-year RFS and OS rates are shown in Table 5. The relapse rate in patients with both MY and TB was nearly five-fold higher than with either one of MY or TB (53.8% vs. 11.4%). Patients with both MY and TB had a much worse 5-year RFS rate than those with either one of MY or TB (44.2% vs. 87.7%). Furthermore, Cox regression analysis showed that there was a significant difference in RFS rate between patients with both MY and TB and those with either one of MY or TB (HR, 5.801;95% CI, 2.0884-16.146; p=0.001). Regarding the OS rate, there was no significant difference between patients with both MY and TB and those with either one of MY or TB on Cox regression analysis.