Real-world patient characteristics and treatment patterns associated with tucatinib therapy in patients with HER2+ metastatic breast cancer.
Authors: Anders Carey K. , Neuberger Edward , Schwartz Naomi RM , Bartley Karen , Hsu Ling-I , Wong Gabriel , Blahna Matthew Thomas , Pittner Brian , Wang Shu , Meisel Jane Lowe 
Published: June 2023

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Background: Tucatinib (TUC) is an oral HER2-targeted therapy approved by the FDA in Apr 2020 for use in combination with trastuzumab and capecitabine (TRA+CAP) for patients with previously treated HER2+ metastatic breast cancer (MBC). In the randomized HER2CLIMB trial, median (95% CI) overall survival (mOS) and progression-free survival (PFS) for patients receiving TUC with TRA+CAP were 21.9 (18.3, 31.0) and 7.8 (7.5, 9.6) months, respectively. Median duration of therapy was 7.3 months. HER2CLIMB used a standard of care comparator arm and included patients with active and stable brain metastasis (BM). HER2CLIMB was conducted prior to approval of fam-trastuzumab deruxtecan (T-DXd) so did not assess the impact of TUC-based therapy following T-DXd. Objective: Describe patient characteristics, treatment patterns, and clinical outcomes for TUC-based treatment in the real-world setting. Methods: This retrospective study included patients in the Komodo Health dataset (aggregating data from patient administrative health claims in the United States) diagnosed with MBC between Jan 1, 2017 and Sep 3, 2022 and initiating TUC post- approval in Apr 2020. Patient characteristics were described in the baseline period (≤6 months from TUC initiation). Key outcomes were time to next treatment (TTNT; as a proxy for PFS), time to discontinuation (TTD), and persistence (proportion continuing treatment at each timepoint) in all TUC-treated patients, and in patients receiving TUC immediately following T-DXd. Results: Of 16,990 patients identified with HER2+ MBC, 528 received TUC-based treatment. Of these, 57 (11%), 164 (31%), 154 (29%), and 153 (29%) received TUC in first-line (1L), second-line (2L), third-line (3L), and fourth-line or later (4L+), respectively. Median follow-up from TUC initiation was 9 months. Overall, 400 patients (76%) had BM prior to initiating TUC (43 [75%], 138 [84%], 111 [72%], and 108 [71%] in 1L, 2L, 3L, and 4L+, respectively). Median (95% CI) TTNT was 10.7 (9.4, 13.1) months overall and 11.5 (9.6, 14.4) in patients receiving TUC in 2L or 3L. Median (95% CI) TTD was 8.5 (7.2, 9.3) months overall, and 9.1 (7.7, 9.9) in patients receiving TUC in 2L or 3L. TUC persistence in the overall cohort was 46% (91/200) at 12 months and 35% (40/115) at 18 months. Sixty-one patients (12%) received TUC immediately following T-DXd (median 4L; 12 in 2L/3L, 49 in 4L+); of whom 36 (59%) had BM prior to initiating TUC. TTNT and TTD for patients treated with TUC following T-DXd were 7.5 (5, 13.3) and 7.3 (3.2, 9.5) months, respectively. Conclusions: In the real-world setting, a higher proportion of patients receiving TUC had BM compared with the HER2CLIMB patient population. TUC-based treatment in the real world is used in multiple lines of therapy and is associated with a similar TTNT and TTD to PFS observed in HER2CLIMB, inclusive of a cohort of patients who received TUC following T-DXd therapy.