In epithelial-to-mesenchymal transition (EMT) epithelial cancer cells achieve mesenchymal features, essentially helping them to metastasize. There is some evidence that EMT could be increased in triple-negative (TNBC) or basal-like breast cancers, although more precise mechanisms considering e.g. EMT-regulating transcription factors are largely unknown. We assessed immunohistochemically vimentin (separately in in situ areas and in invasive cells) as an indicator of EMT, and also EMT-regulating transcription factors zeb1 (separately in stroma and tumour) and Sip1 (in nuclei and cytoplasm) in histological samples of 231 women with local or locally advanced invasive breast cancer. 51.1 % of patients had TNBC and 48.9 % oestrogen and progesterone receptor-positive and HER2 negative breast cancer. Basal-like breast cancers were defined as TNBC that also expressed epidermal growth factor receptor EGFR and/or cytokeratin 5/6. Vimentin expression in invasive cells was higher in TNBCs (p = 9 × 10(-12)) compared to non-TNBC tumours. Vimentin (p = 2 × 10(-6)), nuclear Sip1 (p = 0.035) and zeb1 in stroma (p = 0.013) were overexpressed in basal-like cancers compared to non-basal-like TNBCs. In non-TNBC group findings between studied markers and clinicopathological factors were rare. However, in TNBC cases, vimentin expression in invasive cells associated with poor differentiation (p = 0.00007), zeb1 expression in cancer cells with higher grade (p = 0.002), vascular invasion (p = 0.036) and larger T-class (p = 0.027), whereas stromal zeb1 associated with lymphatic vessel invasion (p = 0.036) and vascular invasion (p = 0.039). High nuclear Sip1 expression was prognostic for poor disease-free survival (p = 0.002) in the whole cohort. The current results emphasize the increased role of EMT in TNBC and especially in basal-like breast cancers. These observations also support the role of studied parameters in tumour progression.