Breast cancer (BC) is the leading cause of cancer deaths in women. One of the reasons for the failure of BC treatment is reportedly the ineffectiveness of chemotherapeutic drugs against breast cancer stem-like cells (BCSCs). HER2 receptors have an important role in the self-renewal of BCSCs. Matrix metalloproteinase (MMP) and cytokine levels were found to be higher in BCSCs, which demonstrates their potential metastatic capacity. Therefore, the aim of this study was to evaluate the response of BCSCs to trastuzumab and to investigate the MMP levels in primary breast cancer cells and HER2+ BCSCs. Tumour tissue samples were obtained during surgical intervention from ten breast cancer patients, and primary culture cells were established from these tissues. Four major molecular subgroups were sorted from the primary culture: HER2+ BCSCs (CD44+CD24−HER2+), HER2− BCSCs (CD44+CD24−HER2−), HER2− primary culture cells (CD44+CD24+HER2−) and triple positive primary culture cells (CD44+CD24+HER2+). These cells were cultured and treated with trastuzumab, paclitaxel, carboplatin, and the combination of those three drugs for 96 h. Cellular responses to these drugs were determined by XTT cytotoxicity test. MMPs and cytokine array analysis showed that MMPs and TIMP-1, TIMP-2 proteins were expressed more in HER2+ BCSCs than in primary culture. HER2− BCSCs were more resistant to drugs than HER2+ BCSCs. Our findings suggest that the presence of HER2− BCSCs may be responsible for primary trastuzumab resistance in HER2+ BC cell population. Further studies investigating the function of MMPs are needed for drug targeting of BCSCs.