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    • br Materials and methods br Statistical analysis

    2018-10-29


    Materials and methods
    Statistical analysis The statistical end point of the analyses was the disease-free survival (DFS) from the date of surgery. Group distributions for each clinicopathologic trait were compared using two-tailed Fisher\'s exact procedure and the chi-square test. Numerical values were compared using Student t test. Data are expressed as mean ± standard deviation. Kaplan–Meier survival curves were plotted and compared using the log-rank test. A multivariate analysis was performed using the Cox proportional hazard model. Statistical significance was defined as p < 0.05. Statistical analyses were performed using SPSS for Windows version 13.0 software.
    Discussion Patients with stage I CRC have an excellent prognosis after oncologic resection, with reported 5-year survival rates of about 90%. Our results showed that 5-year DFS of stage I CRC patients was 88.7%, which was compatible with the results of previous studies. Based on the evidence from multiple statistically robust published trials and the fact that these are generally used in patient management, tumor depth, LVI, and the CEA level can be classified as Category I prognosticators. However, we identified only LVI as the independent prognostic factor of the outcome of stage I CRC patients. For stage I disease, the cause of tumor recurrence or metastasis must be an undetected or undetectable local or systemic residual of the tumor at operation. Evidence has emerged showing a significant amount of nodal metastases of 2 mm or less, likely to be missed during conventional gross pathological specimen examination. Tumors with LVI might be an indicator of occult or undetectable metastasis. In a previous study, immunohistochemical assessment showed that LVI was associated with the presence of micrometastasis in patients with N0 stage. Also, several studies demonstrated that in T1 or T2 CRC, LVI was the independent predictor of gsk-3 node metastases, as shown by multivariate analysis. Recently, a prospective study demonstrated that primary colon cancer with extension to the muscularis propria or beyond, LVI, or high tumor grade correlated with occult metastases in regional lymph nodes. The possible progression steps are now established, and LVI plays an important role in the formation of occult metastasis. However, the recent NCCN guideline did not suggest that such stage I CRC patients should receive chemotherapy. Since the prognosis of stage I CRC patients with LVI is poor, an aggressive follow-up should be recommended in such patients. Although in our study there was a trend showing that patients with a T2 lesion or high CEA level had a poor outcome in the stage I disease, the difference was not significant. The possible explanation appears to be the small sample size. To achieve statistical significance supporting the T2 lesion or high CEA level as a prognostic factor for patients with stage I disease, the estimated minimum sample size should probably be 1000 or above. The recent nationwide study from Germany demonstrated that the impact of the T2 stage is twice that of the T1 stage for colorectal patients. For stage II diseases, several professional organizations have proposed a minimum node yield of 12 to allow accurate staging. For stage I disease, recent analysis of pathological staging from the SEER database suggested that at least four lymph nodes should be harvested to achieve a probability of correct staging of 90%. In our study, the mean number of lymph nodes harvested in T1 and T2 disease was 12.3 ± 8.6 and 15.2 ± 10.3, respectively.In about 40% and 7% of cases, the number of lymph nodes harvested was less than 12 and 4, respectively. However, the outcome of these patients was similar to those who had a higher lymph node harvest with a cutoff value of either 12 or 4 lymph nodes. The number 12 or 4 probably does not hold any particular biological significance. The true effect of lymphadenectomy remains debated, as does the minimum number of nodes necessary for an adequate resection. The possible benefit might be more likelihood of actually identifying stage III disease patients or possibly decreasing local recurrence by resection of affected lymph nodes.