Effective factors in the appearance of metastasis in patients with breast cancer using frailty model

There are various factors effective in the appearance of metastasis that have been surveyed and recognized in different studies. However, the appearance of metastasis by determination of these factors cannot be predicted. One of the models used for the analysis of recurrent data and consideration of heterogeneity between patients is frailty model.

In this survival study, 133 women with breast cancer were treated in Fayazbakhsh Hospital, Tehran, during 2005-2007. All patients were followed until April 2011. Frailty model was employed for the analysis of data and gamma frailty distribution was assumed with the average one and Ө variance. All statistical methods were run in R software.

Disease-free survival rates for 3 and 5 years were 0.78 and 0.72, respectively. During the follow-up period, the risk of metastasis was estimated to be 43%. Two factors were identified as the prognostic factors in the appearance of metastasis: tumor malignancy grade and the number of positive lymph nodes. Frailty variance was 4.27 (P=0.001).

The significant variance of frailty component in the model indicates that patients who have identical explanatory variables face different levels of risk experiencing metastasis. Also, specific characteristics of the patients are important in the incidence of metastasis.