Breast cancer (BC) is one of the most prevalent forms of cancer in women worldwide. Clinical research indicates that BC patients are at an increased risk for thrombotic events, drastically decreasing their quality-of-life and treatment outcomes. There is ample evidence of this in the literature, but it is mainly focused on metastatic BC. Therefore, coagulopathies of nonmetastatic BC are understudied and require in-depth investigation. In this study, clot kinetics and ultrastructure were used to investigate treatment-naïve, nonmetastatic BC patients using scanning electron microscopy, Thromboelastography®, and confocal laser scanning microscopy. It was demonstrated that nonmetastatic BC patients exhibit minimal ultrastructural alterations of the clot components and no changes in the clot kinetics. However, BC patients presented changes to fibrinogen protein structure, compared to matched controls, using an amyloid-selective stain. Together, these findings suggest that coagulation dysfunction(s) in BC patients with early disease manifest at the microlevel, rather than the macrolevel. This study presents novel insights to a method that are more sensitive to coagulation changes in this specific patient group, emphasizing that the coagulation system may react in different forms to the disease, depending on the progression of the disease itself.