Background: Data characterizing LTS with HER2+ MBC are limited. The objective of this analysis is to describe LTS in terms of demographics, disease characteristics, and treatment history. Methods: registHER is an observational cohort of patients (pts) (N=1,001) with HER2+ MBC diagnosed w/in 6 mos of enrollment and followed until death, disenrollment, or 6/09 (median follow-up 27 mos). LTS were defined as pts who survived ≥36 mos from metastatic diagnosis (dx) (n=404). Baseline characteristics were examined. Multivariate analyses assessed factors associated with overall survival (OS) in all registHER pts. Results: Median progression-free survival in LTS was 17.9 mos (95% confidence interval (CI) 15.5-20.2). Similar to all registHER pts, median age at enrollment for LTS was 52 y (range 22,82), the majority were white (85.4%), and initial dx in over half of pts was stage I-III, MBC >12 mos (57.4%). LTS, however, were more likely to have estrogen receptor (ER)+ or progesterone receptor (PR)+ disease (61.6% and 52.9%, respectively) and a lower rate of underlying cardiovascular disease (CVD) (12.4% and 17.2%, respectively). First-line taxane and first-line trastuzumab use was higher in LTS pts. Physician-assessed first-line complete response was 40% in LTS and 22.8% in all registHER pts. Factors associated with OS in all registHER pts are shown in the table. Conclusions: This descriptive study examines factors commonly associated with long-term survival in pts with HER2+ MBC. LTS were primarily white, with ER+ or PR+ disease, and low rates of underlying CVD. Further study is needed to quantify the contribution of these factors to prolonging survival.

Variable	Hazard ratio (95% CI)
Age at enrollment (≥65 y)	1.23 (1.00-1.53)
Race (non-white)	1.31 (1.07-1.61)
Eastern Cooperative Oncology Group (2+ vs. 0-1)	1.94 (1.37-2.74)
Serum albumin (≤3.5 g/dL)	1.52 (1.18-1.96)
ER/PR status (ER+ or PR+)	0.66 (0.55-0.79)
Stage, initial dx (vs. IV) I-III, MBC ≤12 mos I-III, MBC >12 mos	1.51 (1.13-2.00) 1.11 (0.90-1.37)
Metastatic site (vs. visceral/other) Central nervous system, any Bone only or bone+breast Node/local	1.40 (1.03-1.89) 0.61 (0.46-0.81) 0.72 (0.56-0.92)
First-line trastuzumab	0.73 (0.58-0.92)
First-line taxane	0.73 (0.61-0.87)