Haleh aghamolaey - Department of Biostatistics, Faculty of Paramedical sciences, Shahid Behesti university of medical sciences, Tehran, Iran
Ramin aghamolaei - Department of Pharmaceutics, Faculty of Pharmacy, Shahid sodoughi university of medical sciences, Yazd, Iran
Ahmad Reza baghestani - Physiotherapy Research Center, Department of Biostatistics, Faculty of Paramedical Sciences, Shahid Beheshti University of Medical Sciences
Mohammad Esmaeil akbari - Cancer research center, Shahid Behesti university of medical sciences, Tehran, Iran

Introduction & Aim: Breast cancer is one of the most common malignancies in women and the first common cancer and the third leading cause of death among Iranian women. The aim of the current study was to show how the Weibull distribution with non-constant shape parameter as a new method works on determining prognostics factors. Methods: We used the data collected from 438 female patients with breast cancer registered in the Cancer Research Center in Shahid Beheshti University of Medical Sciences, Tehran, Iran. The patients had been diagnosed from 1992 to 2012 and were followed up until October 2014. To identify clinical, pathological, and biological characteristics of patients that might have had an effect on survival of the patients Weibull with non-constant shape were used. Analyses were performed using SAS. The significance level was set at P ≤ 0.05. Results: A total of 75 patients (17.1%) died due to breast cancer during the study. Age, numbers of metastatic lymph nodes, tumor size, stage, ER and PR receptors and histologic grade were significant factors. Conclusion: In this study, there is a difference on interpretation of the significant factors between the regular Weibull and this one we used and that is hazard ratio which is not constant anymore and is time dependent.