To our knowledge, this study is the first one to show the relationship between BD grade and T stage in patients with pStage II CRC as a prognostic value for recurrence. In the initial analysis, T4 stage and BD3 grade were identified as independent risk factors affecting RFS. Furthermore, the primary analysis demonstrated that the 5-year RFS rate in the BD3+/T4+ group was significantly lower than that in the BD3+/T4- group (66.2 vs. 74.6%) (P=0.0079). These results suggest that pStage II CRC patients who had both BD3 and T4 stage factors had a poorer prognosis than those with other high-risk factors.
A recent study reported that the tumor microenvironment at the invasive front, including the BD, played an important role in CRC outcomes.14 The intensity of BD grade and fibrotic immature stroma promotes de-differentiation and dissemination of cancer cells and the first step of invasion. On the other hand, T stage is known to be a significant risk factor for recurrence in all cancer types. In the SACURA trial, BD3 (T4 rate: 26.8%) was associated with a poorer prognosis than BD1 (T4 rate: 10.4%) and BD2 (T4 rate: 16.0%), although the BD3 group had a higher T4 rate.12 The prognosis in the BD3 group might be strongly influenced by the T4 stage in the SACURA trial. In the present study, we revealed that pStage II CRC patients with both BD3 and T4 factors had much poorer prognosis.
The 5-year RFS rate of 66.2% in the BD3+/T4+ group is similar to that of stage IIIC colon cancer. Moreover, in the BD3+/T4+ group, the recurrence rate was lower in the adjuvant chemotherapy group (HR 1.99, 95% CI 0.38–10.36, P=0.4024), although the significant superiority of adjuvant chemotherapy was not shown. This might be due to the insufficient efficacy of adjuvant chemotherapy because only one out of nine patients was administered a doublet regimen including oxaliplatin. In the ACTS-CC 02 trial, the oxaliplatin-based regimen was more effective than UFT/leucovorin in advanced disease, such as stage IIIC and N2b.15 In addition, in the AHIEVE-2 trial, which compared the 3-month with 6-month CAPOX or mFOLFOX6 regimens as adjuvant treatment, the non-inferiority of 3-month treatments was not shown and the 3-year disease-free survival (DFS) rate inT4 stage patients was less favorable in the 3-month treatments than in the 6-month treatments (3-month 76.2% vs. 6 month 79.7%, HR 1.28 [0.68–2.43]).16 The 6-month oxaliplatin-based regimen might improve the prognosis in both BD3 and T4 stage patients.
Recently, several predictive biomarkers for recurrence in stage II colon cancer have been examined. Stage II colon cancer patients with microsatellite instability-high (MSI-H) had a good prognosis, and fluoropyrimidine-based adjuvant chemotherapy had no effect on DFS and OS.17 In the SACURA trial, MSI-H was observed in 7.2%, and the 5-year RFS rate in MSI-H patients was 92.9%, which was better than that in non-MSI-H patients (HR 0.40, 95% CI 0.17–0.98, P=0.045).18 Moreover, there was no difference in the 5-year RFS rate between the adjuvant chemotherapy group and surgery-alone group (94.3 vs. 91.7%). In stage II colon cancer with MSI-H, adjuvant chemotherapy might be unnecessary. However, MSI testing requires immunohistochemistry, expensive gene analyses, and clinical evidence supporting their use is still insufficient.
In addition, recently, circulating tumor DNA (ctDNA), which are short nucleic acid fragments thought to be released in the systemic circulation as a result of tumor cell apoptosis or necrosis,19,20 has emerged as a promising biomarker of disease status for metastatic cancer.21–23 Moreover, the detection of ctDNA after curative resection of stage II colon cancer might identify patients who are at the highest risk of recurrence and help inform adjuvant treatment decisions. Among the patients with positive ctDNA after curative resection, 79% experienced recurrence, whereas 9.8% experienced recurrence with negative ctDNA after curative resection (HR 18, 95% CI 7.9–40, P<0.00).24 Although ctDNA cannot be measured in routine clinical practice, ctDNA might be superior to other clinicopathological measures as prognostic factors.
In the initial analysis, the number of examined lymph nodes was identified as a risk factor affecting RFS in multivariate analysis. Although the number of dissected lymph nodes was considered sufficient when 12 or more lymph nodes had been examined pathologically, this number depends on the length of the dissection or the location of the right or left side. Therefore, definitive evidence as a prognostic factor has been lacking. Lymph or venous invasion, perineural invasion, and histologic type were not associated with statistically significant risk factors for recurrence in the present study. Indeed, in the SACURA trial, there were no relationships between these factors and prognosis. Furthermore, the frequency of these factors was much lower than that of other prognostic factors, although perforation or intestinal obstruction might be a poor prognostic factor in NCCN guidelines.3
Our study had several limitations. First, the present study had a retrospective design in a single institution. Second, the location of the rectum was a poor prognostic factor and 42% of the patients enrolled in this study had rectal cancer. However, in patients with only colon cancer excluding the rectum, the 5-year RFS rate in those with both BD3 and T4 was also shown to be significantly lower than those in the other two groups. Third, the pathologic results might have differed among pathologists because pathological evaluation including BD was not performed by determined pathologists. Fourth, the MSI, which is considered predictive in the NCCN guideline,3 was not examined in the present study.
In conclusion, this study indicated that patients with pStage II CRC with both BD3 and T4 had clearly poorer prognostic features than those with only BD3 or T4 factors. We believe that doublet adjuvant chemotherapy, including oxaliplatin, should be considered for patients with pStage II CRC with both BD3 and T4 stages.