High circulating HER2 extracellular domain levels correlate with reduced efficacy of an aromatase inhibitor in hormone receptor-positive metastatic breast cancer: a confirmatory prospective study.
BACKGROUND
In this specifically designed, prospective study, the authors addressed the predictive value of circulating levels of the extracellular domain (ECD) of HER2 in patients with metastatic breast cancer who were treated with letrozole.


METHODS
Two hundred twenty-six patients with hormone receptor-positive, metastatic breast cancer received letrozole (2.5 mg daily) until they developed either disease progression or unacceptable toxicity. Efficacy was measured primarily as the time to progression (TTP) and, secondarily, as the objective response rate (ORR) and overall survival. HER2 ECD levels were determined by using a sandwich enzyme HER2/neu immunoassay before letrozole treatment was initiated. Positive HER2 ECD status was correlated with treatment efficacy.


RESULTS
Forty-two patients (19%) had elevated HER2 ECD levels, which were associated with primary tumor HER2 expression (P < .001) but not with age, performance status, location, or number of metastatic sites. The median TTP was significantly shorter among patients who had elevated HER2 ECD compared with the median TTP among patients who had normal levels (4 months vs 14 months; P = .0004), and the ORR was lower in the group with elevated HER2 ECD levels (14% vs 30%; P < .036). Overall survival was significantly shorter among patients with elevated serum HER-2 ECD (P < .0005).


CONCLUSIONS
Elevated HER2 ECD concentrations predicted poorer outcomes in postmenopausal women with metastatic hormone receptor-positive breast cancer who were treated with aromatase inhibitors like letrozole.
Colomer
Ramon
R
M. D. Anderson Cancer Center Spain, Madrid, Spain. rcolomer@seom.org
Llombart-Cussac
Antonio
A
Lloveras
Belen
B
Ramos
Manuel
M
Mayordomo
Jose I
JI
Fernández
Roberto
R
Tusquets
Ignasi
I
Gil
Miguel
M
Barnadas
Agustí
A
Constenla
Manuel
M
Gilabert
Montserrat
M
Alba
Emilio
E
D047072:Aromatase Inhibitors / Q000627:therapeutic use*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D015331:Cohort Studies; D005260:Female; D006801:Humans; D000077289:Letrozole; D009362:Neoplasm Metastasis; D009570:Nitriles / Q000627:therapeutic use*; D011446:Prospective Studies; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000097:blood*; D011960:Receptors, Estrogen / Q000378:metabolism*; D011980:Receptors, Progesterone / Q000378:metabolism*; D016896:Treatment Outcome; D014230:Triazoles / Q000627:therapeutic use*
D047072:Aromatase Inhibitors; D000077289:Letrozole; D009570:Nitriles; D018719:Erb-b2 Receptor Tyrosine Kinases; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; D014230:Triazoles