ABSTRACT
Competing risk data is one of the multivarite survival data. Competing risk data can be modelled using copula function. In this study we propose a bayesian modelling approach of competing risk data using the copula function. We used the data from colorectal cancer registyrarty in Tehran. After constructing likelihood function using Clayton copula by choosing appropriate prior distribution for parameters, we obtained the posterior distribution of parameters using the Metropolis-Hastings algorithms and Slice sampling. The results of univariate analysis showed that sex, histology of tumor, extent of wall penetration, lymph node metastasis, distant metastasis and pathological stage of tumor were significantly associated with colon cancer and sex, histology of tumor, lymph node metastasis, distant metastasis and pathological stage of tumor were were significantly related to rectal cancer. In the multivariate analysis, age at diagnosis, tumor grade and distant metastasis were significant prognostic factors for colon cancer and tumor grade and size of the tumor were significant prognostic factors of rectal cancerAs we showed some variables may have different impacts on colon and rectum cancers, consequently, further studies are needed to be conducted considering risk factors of these cancers separately
ABSTRACT
Oxaliplatin [OX] significantly enhanced the antitumor activity of 5-FU in patients with advanced colorectal cancer and recently some phase II trials have evaluated the feasibility and efficacy of oxaliplatin in neoadjuvant setting for treatment of locally advanced rectal cancer. On the other hand various studies have demonstrated that the overexpression of thymidylate synthase [TS] can induce resistance to 5-FU in colorectal carcinoma. The aim of this study was to assess the value of TS expression as a predictive factor in the efficacy of neoadjuvant chemoradiation with and without oxaliplatin in rectal cancer. This study was performed in 61 patients [that ultimately 50 patients had including criteria] with locally advanced rectal adenocarcinoma that inferior margin of the tumor had to be located no farther than 6 cm from the anal verge. Preoperative radiotherapy was delivered to the pelvis with CO 60 to 50/4 Gy. All patients received simultaneous chemotherapy: 5-fluorouracil [5-FU], 300 mg/square meter i.v. 24 h infusion during radiotherapy on days 1-5 every week. Thirty patients received oxaliplatin 50-60 mg /square meter weekly during radiotherapy.TS expression was assessed by immunohistochemical staining technique in pretreatment specimen, and the patients were categorized into TS [+] and TS [-] groups. A total of 23 of 50 tumors showed TS positive status at biopsy [46%] . Overall 36 patients [72%] achieved pathologic response [40% complete and 32% partial] that was significantly better in the TS [-] group than in the TS [+] group [85.1 vs 56.5%, p=0.024] and in the OX [+] group than in the OX [-] group [86.6 vs 50%, p=0.005]. Among TS [-] patients there was no difference in pathologic response [88.2 vs 80%, p=0.561] or sphincter preservation [76.4 vs 80%, p= 0.831] as a result of whether oxaliplatin therapy was carried out or not. But among the TS [+] patients there was a significant gain in pathologic response [84.6 vs 20 %, p=0.002] and sphincter preservation [84.6 vs 40 %, p= 0.026] in favor of oxaliplatin group. Our study indicate that oxaliplatin can improves poor outcome of TS positive rectal cancer and TS expression may be used for selecting patients for oxaliplatin containing neoadjuvant chemoradiation protocols that can have major role in the tumor down staging and preservation of sphincter and ultimately better quality of life