Family history is a known risk factor for breast cancer, but its prognostic value and the prognostic value of tumour characteristics in relation to family history has not been clearly established. In addition, studies of intra-familial tumour characteristics and prognosis in population-based settings are very rare. Two previous studies have suggested that breast cancer prognosis clusters within families. However, both studies lack information on HER2 expression status, which is a strong prognostic factor and could contribute to the observed results.