Behavior of metastatic breast cancer according to subtype.

PURPOSE: To explore the impact of breast cancer subtype on metastatic behavior and long-term outcome defined as breast cancer specific survival (BCSS). METHODS: Retrospective single centre cross-sectional study of 5972 patients with newly diagnosed, unilateral first diagnosis of breast cancer, diagnosed 2000-2010. Patients had either early breast cancer (EBC) treated primarily by surgery (SURG n = 5072), neoadjuvant systemic therapy (NEO n = 592), or upfront metastatic disease (META n = 308). Surrogate breast cancer subtypes were defined according to classical pathological criteria. Analysis was performed using Kaplan-Meier method and logistic/Cox regression. RESULTS: After median follow-up time of 103.6 months (IQR 73.4-139.2 months), 817 patients with EBC at diagnosis (14.4%) developed distant metastases of which 621 (12.2%) SURG and 196 (33.1%) NEO. Metastasis rate after EBC was: LuminalA 8.1%, LuminalB1(HER2-) 20.4%, LuminalB2(HER2+) without (neo)adjuvant trastuzumab 21.7%, LuminalB2(HER2+) with trastuzumab 9.0%, HER2Positive(ER-) without trastuzumab 30.0%, HER2Positive(ER-) with trastuzumab 19.9% and TripleNegative 25.3%. There were major differences in site of first metastases according to subtype. For single site first metastases, median BCSS assessed from time of metastases was worst for brain localization (13.9 months) and best for bone (48.4 months). Multiple sites of first metastases had worse BCSS from date of metastases than single site first metastases (median BCSS for 1 site 40.0, 2 sites 27.1, ≥ 3 sites 20.5 months). Median BCSS from date of metastases is longer in upfront metastases compared to secondary metastases after EBC (43.4 vs. 27.9 months). CONCLUSIONS: Tumor subtype influences the metastatic behavior and survival after development of distant metastases.