In conclusion our results show that the well-established prognostic factors in BC, including Ki67, are still valid for ILC’s, and the combination of Ki67, histological grade and ER into KiGE, together with tumour size and nodal status makes it possible to identify a large group of ILC patients (37%) with a long-term natural history associated with such a good prognosis, that chemotherapy can be safely avoided and exclusion of endocrine therapy considered. Here, ESR1 is linked to breast cancer.