Triple negative breast cancers (TNBCs) are defined as estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor-2 (HER2) negative. TNBCs, accounting for about 11-20% of invasive breast cancers, are more aggressive, have a poorer prognosis, and have few targeted treatment options, compared with hormone-sensitive breast cancers. A growing body of literature suggests post- diagnosis, lifestyle-related factors may impact overall breast cancer prognosis. However, little is known about the role of modifiable lifestyle-related factors in TNBC prognosis. To date, no prospective cohort study has investigated lifestyle-related factors that have been implicated in breast cancer prognosis overall, specifically in the prognosis of TNBC. This effort has not been feasible in the past due primarily to the need for data on post- diagnosis lifestyle factors and breast cancer outcomes in a large population of women with TNBC. The proposed study will overcome these limitations by using the resources of the After Breast Cancer Pooling Project (ABCPP), a collaborative project that includes four prospective cohorts of breast cancer survivors, for which we have successfully pooled and harmonized data on clinical characteristics and lifestyle factors. With the addition of two more ongoing cohort studies, we anticipate a total of approximately 1,550 women diagnosed with invasive TNBC recruited from the United States, the United Kingdom, and Shanghai, China. Our overall hypothesis is that the associations of lifestyle-related factors with breast cancer recurrence and mortality may differ for women with TNBC, as compared to women with ER+ breast cancer, depending on the underlying biological mechanisms for each lifestyle factor-breast cancer outcome association. To investigate this hypothesis, we propose to evaluate the associations of post-diagnosis body mass index, weight change, post-diagnosis recreational physical activity, and select dietary factors suggested to be associated with breast cancer prognosis overall (i.e., soy food intake, vegetable intake, alcohol consumption, and tea consumption) with recurrence, breast cancer-specific mortality, and total mortality among women (1) with TNBC and (2) with ER+ breast cancer. The proposed collaborative study, which will pool the resources of six prospective cohorts of breast cancer survivors, will be the first study that is sufficiently powered to investigate the effect of modifible lifestyle-related factors on TNBC prognosis. The findings of our study will lead to public health recommendations and guidelines appropriate for breast cancer survivors with TNBC, information critically needed, with the ultimate goal of reducing morbidity and mortality among breast cancer survivors. This study, building upon an existing collaborative pooling project and experienced research team, is cost-effective. Further, the proposed project will help sustain collaborative research efforts to promote future pooled analyses in the ABCPP.