Estrogen receptor quantitative measures and breast cancer survival

While the estrogen receptor (ER) is the single most widely used biomarker to evaluate breast cancer outcomes, aspects of ER marker biology remain poorly understood. We sought to determine whether quantitative measures of ER, such as protein expression and intensity, were associated with survival, or with survival disparities experienced by Hispanic women.

A case-cohort study included a 15% random sample of invasive breast cancer cases diagnosed from 1997 to 2009 in six New Mexico counties and all deaths due to breast cancer-related causes. Pathology reports and tissue microarrays served as sources of ER information. Analyses were restricted to women with ≥1% ER immunohistochemical staining. Hazard ratios (HR) and 95% confidence intervals (CI) for breast cancer death were estimated using Cox proportional hazards models.

Included women represented 4336 ER+ breast cancer cases and 448 deaths. Median follow-up was 93 months. ER percent expression was not associated with breast cancer survival after adjustment for standard prognostic factors (p trend = 0.76). ER intensity remained a strong and independent risk factor for breast cancer survival in multivariate analyses: Women whose tumors expressed ER at intensity = 2 (HR 0.6; 95% CI 0.4-1.0) or 3 (HR 0.5; 95% CI 0.2-0.9) had a reduced risk of breast cancer mortality, compared to ER intensity = 1 (p trend = 0.02). Neither ER protein expression nor intensity influenced Hispanic survival disparities.

Estrogen receptor percent positive staining is not independently related to breast cancer survival after adjustment for other survival-related factors. ER intensity, in contrast, demonstrates promise for prognostic utility.