[Lani]

Two hundred and forty-eight potentially eligible patients were identified (Supplemental Figure S1). Patients with in-breast recurrence (N = 11), patients with locoregional recurrence only (N = 14), patients who did not receive at least 21 days of trastuzumab or lapatinib therapy after diagnosis of recurrent disease (N = 28), and patients who were subsequently determined to not have HER2-positive recurrent disease (N = 13) were excluded. In addition, patients with only a single clinic visit at the institution (N = 14) were excluded because of lack of data about treatments administered. A total of 168 patients were eligible and included in the analysis.
Demographic factors and primary and metastatic tumor pathological characteristics for all eligible patients are given in Supplemental Table S1. Mean age at initial diagnosis of breast cancer was 47.9 (range 25.3–91.9). At initial diagnosis, 77 (46 %) patients had grade 3 disease, 101 (60 %) had HR-positive disease, and 49 (29 %) had stage 4 disease. Twenty patients (12 %) received adjuvant trastuzumab.
Median time to distant metastatic disease was 2.2 years (range 0–19.2 years). All 168 patients had radiographic evidence of distant metastases. Ninety-six (57 %) underwent biopsy to confirm distant metastasis. Sixty-six (39 %) patients developed CNS metastases during their disease course; it was the initial metastatic site of disease for 7 (4 %) patients.
Timing of initiation of HER2-targeting therapy was influenced by the year of diagnosis and duration of survival. In this cohort, first-line systemic therapy for metastatic disease contained trastuzumab for 71 %, lapatinib for 2 %, and endocrine therapy or chemotherapy without HER2-targeted therapy for 26.2 %. Forty-six patients received treatment with lapatinib (27 %), 18 (11 %) received ado-trastuzumab emtansine, and 15 (9 %) received pertuzumab as part of their second-line or later treatment regimens.