(HealthDay News) – Patients with human epidermal growth factor receptor 2 (HER2)-positive advanced breast cancer whose tumors also express hormone receptors may be less responsive to the addition of trastuzumab to chemotherapy, suggesting that hormone-receptor expression has a predictive role in determining response to therapy, according to research published in the January 1 issue of Cancer.

Filippo Montemurro, MD, of the Institute for Cancer Research and Treatment in Torino, Italy, and colleagues investigated whether or not there was a relationship between quantitative immunohistochemical hormone receptor expression and response to the combination of trastuzumab with chemotherapy in HER2-positive advanced breast cancer. Specifically, they studied the effect of hormone-receptor expression on overall response rate and progression-free survival (PFS) in 227 consecutive patients receiving trastuzumab-based treatment; 111 patients (49 percent) had hormone receptor-positive tumors (defined as ≥1 percent of tumor cells positive for estrogen receptor, progesterone receptor, or both).

The researchers found that, overall, patients with tumors expressing high levels of estrogen receptor (≥30 percent of cells) were significantly less likely to achieve an objective tumor response. Patients with hormone receptor-positive tumors achieved a significant PFS benefit when maintenance endocrine therapy was added to trastuzumab after completion of chemotherapy.

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“The PFS prolongation seen in patients adding endocrine therapy to trastuzumab upon the completion of chemotherapy suggests that these tumors retain endocrine responsiveness. If confirmed in independent datasets, this predictive role of hormone-receptor expression would have therapeutic implications,” the authors write.

One author disclosed receiving honoraria from GlaxoSmithKline.

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