Distribution and prognosis of molecular breast cancer subtypes defined by immunohistochemical biomarkers in a Spanish population-based study.

Background: The objective of this study is to analyze the distribution, clinicopathological features, relative survival rate and excess risk of death among females diagnosed with invasive breast cancer and classified by molecular subtype from ten Spanish cancer registries.

Method: Three thousand four hundred and eighty incident cases of women - mostly diagnosed in 2005 - were classified into five molecular subtypes according to immunohistochemical status of hormonal receptors and HER2 (human epidermal growth factor receptor 2): estrogen receptor (ER) and/or progesterone receptor (PR)+ and HER2-, ER+ and/or PR+ and HER2+, HER2-overexpressed (ER-, PR- and HER2+), triple negative (ER, PR and HER2-) and unclassified (hormonal receptor or/and HER2 unknown). Relative survival rates at 1, 3 and 5years and relative excess risks (RER) of death adjusting for molecular subtype, age, stage and histological grade were estimated.