e13031 Background: Some breast cancer subtype-specific demographics and histopathological characteristics can be associated with metastatic outcome. Semi-quantitative oestrogen receptor (sqER) is prognostic in ER-positive HER2-negative tumours. Here, we studied sqER for outcome in early diagnosed triple positive breast cancers (TPBC;ER+/PR+/HER2+). Methods: Retrospective monocentric study of all consecutive early diagnosed TPBC (July 2002 - Dec 2017). Immunohistochemistry (IHC) was used for ER, PR and HER2; IHC ≥1% ER/PR was pos; HER2 was FISH-confirmed. Low sqER was defined as Allred score < 7/8. Local therapy was surgery +/- radiotherapy; systemic treatment was (neo)-adjuvant chemotherapy and trastuzumab and endocrine treatment. The clinicopathological variables we studied apart from sqER were age, menopausal status, BMI, parity, tumor grade and clinical stage at diagnosis. Variables were analysed by a Fishers Exact or Mann-Whitney U test. All reported p-values are two-sided. Cox regression was used to investigate howqER is associated with distant metastasis. Results: We included 415 female patients. 18% had low sqER; these were younger and more likely premenopausal at diagnosis; p < 0.001. Other studied variables didn’t differ by sqER-expression. 7% developed metastasis after a mean follow up of 86 months. High sqER-TPBCs as compared to low sqER-TPBCs were less likely to metastasize (HR 0.42; 95 CI 0.19-0.91). Conclusions: Low sqER in TPBC, present in about a fifth of these tumours, is typically associated with younger age and premenopausal status at diagnosis. Low sqER TPBC are more likely to metastasize when compared to TPBC with high sqER levels. [Table: see text]