The journey of patients affected by metastatic hormone receptor-positive/HER2-negative breast cancer from CDK 4/6 inhibitors to second-line treatment: A real-world analysis of 701 patients enrolled in the GIM14/BIOMETA study

Purpose: The aim of this study was to evaluate the effectiveness of CDK 4/6 inhibitors (CDK 4-6i) according to HER2 status (low/zero), and endocrine resistance/sensitivity, as well as the efficacy of second-line treatments, in a large real-world cohort. Methods: The GIM14/BIOMETA study (NCT02284581) is a retrospective/prospective study of the Gruppo Italiano Mammella evaluating treatment patterns and survival outcomes in patients with metastatic breast cancer (MBC). We retrieved data on patients with hormone receptor-positive/HER2-negative MBC receiving first-line CDK 4/6i. Results: Among 3832 patients enrolled in the GIM14-BIOMETA study, 701 were eligible. At a median follow-up of 24.80 months, no significant differences were found between HER2-zero and HER2-low subgroups in terms of first-line time to treatment discontinuation (TTD) (26.16 months [IQR 12.84-NR] vs. 27.60 months [IQR 12.12-64.44], p = 0.972) or overall survival (OS) (mOS>60 months for both groups, p = 0.398). Median TTD was 33.24 months (IQR 16.32-NR) for the endocrine sensitive subgroup, 19.92 months (IQR 8.88-51.24) for the secondary endocrine resistant subgroup and 17.40 months (IQR 7.44-24.72) for the primary endocrine resistant subset, respectively (p < 0.001). Among 239 patients receiving second-line treatment, no significant difference (p = 0.188) was found in terms of second-line TTD between those treated with capecitabine (6.11 months, IQR 2.96-11.47), taxane-based chemotherapy (5.06 months, IQR 2.99-9.99), everolimus plus exemestane (5.39 months, IQR 2.53-9.03) or fulvestrant (6.44 months, IQR 3.38-NR). Conclusions: Endocrine therapy plus CDK 4/6i represents an effective treatment, regardless of HER2 status (low/zero). Second-line agents did not differ significantly in terms of TTD. Endocrine resistant cancers exhibit poor response to CDK 4/6i.