During the progression from ductal carcinoma in situ (DCIS) to invasive breast cancer (IBC), cells must overcome the physically restraining basement membrane (BM), which compartmentalizes the epithelium from the stroma. Since the extracellular matrix (ECM) of the epithelial and stromal compartments are biochemically and physically distinct from one another, the progression demands a certain degree of cellular plasticity for a primary tumor to become invasive. The epithelial-to-mesenchymal transition (EMT) depicts such a cell program, equipping cancer cells with features allowing for dissemination from the epithelial entity and stromal invasion at the single-cell level. Here, the reciprocal interference between an altering tumor microenvironment and the EMT phenotype was investigated in vitro. BM-typical collagen IV and stroma-typical collagen I coatings were applied as provisional 2D matrices. Pro-inflammatory growth factors were introduced to improve tissue mimicry. Whereas the growth on coated surfaces only slightly affected the EMT phenotype, the combinatorial action of collagen with growth factor TGF-β1 induced prominent phenotypic changes. However, EMT induction was independent of collagen type, and cellular accessibility for EMT-like changes was strongly cell-line dependent. Summarizing the entire body of data, an EMT-phenotyping model was used to determine cellular EMT status and estimate EMT-like changes. The miR200c-mediated reversion of mesenchymal MDA-MB-231 cells is reflected by our EMT-phenotype model, thus emphasizing its potential to predict the therapeutic efficacy of EMT-targeting drugs in the future.