Evaluation of Factors Related to Short-Term and Long-Term Survival of Breast Cancer Patients by Mixture Cure Model

Introduction: Breast cancer is the most common cancer among women. Today, with advancements in medical sciences, increasing the cure probability of patients as well as increasing survival time is an important goal of cancer treatment. Therefore, in this study, in addition to examining patients’ survival, we investigated the cure probability of breast cancer patients and its prognostic factors using the semiparametric mixture cure model. Methods: This is a retrospective cohort study of 1310 breast cancer patients admitted to Motamed Cancer Institute from 1995 to 2013 and followed up until 2018. The Kaplan-Meier curve and a semiparametric mixture cure model were fitted to data. In this model, patients were divided into two categories of cured and uncured, then the cure rate and the survival rate of uncured patients were calculated, and related factors were identified. Results: Of the 1310 women with breast cancer in the study, 235 (18.1%) cases died and others were censored. Based on the Kaplan-Meier curve, the cure rate was 68%, and the last death case was observed about 12 years after diagnosis. Obesity, lymph node involvement, and mastectomy were identified as risk factors for patients' long-term survival, while larger tumor size, more advanced stage of the disease, and lack of chemotherapy were risk factors for short-term survival. Conclusion: These findings indicate that many prognostic factors for breast cancer are not only important when choosing a treatment strategy in the short term, but they also play an important role in the long-term to identifying high-risk patients and those who still need further follow-up.