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Stronger ER positivity increased endocrine therapy benefit in breast cancer
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Patients with breast cancer who had 10% or more ER-positive tumor cells demonstrated increased benefit from endocrine therapy compared with patients who had weaker ER positivity or ER-negative disease, according to results of a retrospective study.
The analysis included 9,639 patients with primary breast cancer who were treated at The University of Texas MD Anderson Cancer Center between 1990 and 2011.
Researchers categorized patients into 1% and 10% thresholds of ER positivity according to staining by immunohistochemistry. They found 80.5% of patients had tumors that were ≥10% ER-positive, 2.6% of patients had tumors that were 1% to 9% ER-positive, and 16.9% of patients had ER-negative disease or tumors that were ˂1% ER-positive.
Patients with 1% to 9% ER-positive tumors tended to be younger and have more advanced disease than patients with stronger ER positivity.
Median follow-up was 5.1 years. At that time, patients with strong ER positivity demonstrated improved survival compared with patients with 1% to 9% ER positivity.
Survival was comparable between patients with weak ER positivity and ER-negative disease.
“Patients with tumors that are ER-positive 1%-9% have clinical and pathologic characteristics different from those with tumors that are ER-positive ≥10%,” the researchers wrote. “Similar to patients with ER-negative tumors, those with ER-positive 1%-9% disease do not appear to benefit from endocrine therapy; further study of its clinical benefit in this group is warranted. Also, there is a need to better define which patients of this group belong to basal or luminal subtypes.”
Disclosure: See the study for a full list of the researchers’ relevant financial disclosures.
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