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International Journal of Cancer Research

Year: 2005  |  Volume: 1  |  Issue: 2  |  Page No.: 87 - 93

Postoperative Survival in Gastric Cancer Patients and its Associated Factors: A Method Based on a Non-homogenous Semi-Markovian Process

Hojjat Zeraati, Mahmood Mahmoudi, Anoshirvan Kazemnejad and Kazem Mohammad


This study was designed and carried out to determine the five-year survival rate of gastric cancer patients who had undergone surgical treatment at one of the most important cancer treatment centers, the Iran Cancer Institute and to assess its associated factors. During a study period, patients may often experience events that are likely to affect the final outcome as well. Should these intermediate events and their time of occurrence be overlooked, they may bias the results of the study. It has been suggested that such variables be assigned in the model as time-dependent covariates, but using models with joint distribution of time before death and time before an intermediate event (in this study, relapse), although more difficult, will certainly provide more accurate results. In this study we analyzed the data using a non-homogenous semi-Markovian stochastic process, which basically, regarding life span and intensity rate as the stochastic processes, was a doubly stochastic process and recommend it for analyses of similar data. Two hundred and 81 gastric cancer patients with adenocarcinomatous pathology who had been admitted to and operated on at the Iran Cancer Institute between March 1995 and March 1999 were enrolled in this study. The patients` life expectancy after surgery was determined and its relationship with variables of age at the time of surgery, gender and factors related to the disease such as the cancer site, stage, presence of metastases and sites of metastasis were assessed. In the analyses, methods of Kaplan-Meier, Cox proportional hazards model, non-homogenous Markovian process and Breslow estimator were used. The software used for the analyses were S Plus 2000 and R and an alpha level of 0.05 was considered significant. The five-year survival rate and the median life expectancy in the studied patients were 22.6% and 19.00 months, respectively. The Cox proportional hazards model was used to assess the effect of different variables simultaneously and it showed that age, lymph node metastasis, recurrence and disease stage influenced the chances of survival. It was also shown that lymph node metastasis and disease stage correlated with time of recurrence, while age, distant metastasis and disease stage affected survival after recurrence and age correlated with survival of patients without recurrence. Gastric cancer patients in Iran have a low five-year survival rate. One of the most important reasons seems to be delayed consultation and diagnosis. Most patients are seen first with the disease in the late stages. At this point, most have lymph node, liver, or even distant metastases which makes treatment even more complex. Thus, it is necessary to employ mass media for extensive public education about the early warning signs of the disease and performing periodic examinations.

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