Аннотация
Relevance: Triple-negative breast cancer is characterized by an aggressive clinical course, high biological heterogeneity, and the absence of expression of estrogen and progesterone receptors and human epidermal growth factor receptor 2. The introduction of immune checkpoint inhibitors, particularly pembrolizumab, has expanded systemic treatment options. In real-world clinical practice, treatment response varies, ranging from complete pathological response to disease progression, underscoring the importance of analyzing individual clinical trajectories.The study aimed to analyze the treatment characteristics and clinical outcomes of patients with triple-negative breast cancer receiving pembrolizumab as part of comprehensive anticancer therapy.Materials and Methods: Four clinical cases of patients with triple-negative breast cancer who received treatment including pembrolizumab were presented. We retrospectively analyzed disease stage; tumor morphological and immunohistochemical characteristics; Ki-67 proliferative activity index; programmed cell death ligand 1 expression and combined positive score; sequence of systemic and surgical treatment; imaging findings; and clinical outcomes. We assessed pathological response using the Residual Cancer Burden system.Results: Two of the four patients achieved a pathological complete response. In one case, the combined positive score was 10. In the third case, with a combined positive score of 100 and a Ki-67 index of 90%, disease progression was observed following chemoimmunotherapy; after surgical treatment, residual cancer burden class II was determined. In the fourth case, following residual cancer burden class III, pembrolizumab administration was associated with prolonged disease stabilization; as of July 2, 2026, the 29th course of immunotherapy had been administered.Conclusion: This case series demonstrates various clinical and pathological response patterns to comprehensive treatment including pembrolizumab. Differences observed at combined positive scores of 10 and 100 highlight the heterogeneity of individual treatment responses and do not allow a direct association between treatment efficacy and the absolute value of the combined positive score.