Surviving Breast Cancer: A study of cancer recurrence and mortality after mastectomy in postmenopausal women receiving radiotherapy and Tamoxifen

Abstract: This paper analyzes mortality, cancer recurrence (loco-regional, other types of cancer and distant) and the impact of progesterone status on the effect of Tamoxifen using survival analysis methods. The data consists of 258 postmenopausal women from the Southern Sweden health care region with estrogen positive receptor status receiving radiotherapy, Tamoxifen and a combination of those after mastectomy. The period of the study is from 1978 to 2003. Three additional explanatory variables are included in the regression models: patient age, number of positive lymph nodes and tumor size. The combined treatment is found to be significantly better than radiotherapy from the 6th year and on. The death rate is decreased by 36.5 %. The difference in cumulative incidence of loco-regional breast cancer recurrences is significant between the Tamoxifen vs. the combined group and the radiotherapy vs. the combined group. The lowest and highest cumulative incidence of loco-regional recurrences is found in the combined group and Tamoxifen group, respectively. For other types of cancer recurrence (non-breast related), the hazard is 3.27 times higher in the combined treatment group compared to the radiotherapy group. The effect of the treatment variable on distant cancer recurrences interacts with the age variable, i.e. age at the beginning of the study. One extra year of age results in a 10.4 % decrease of the hazard in the radiotherapy group, while the rate of distant recurrence for every additional year of age increases by 1.1 % in the combined group. The progesterone status for the survival rate of patients receiving Tamoxifen is significant. Progesterone status 400 days after the randomization date results in 49.7 % lower hazard in the progesterone receptor positive group compared to the progesterone receptor negative group.