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Differences in Breast Cancer Risk Factors by Tumor Marker Subtypes among Premenopausal Vietnamese and Chinese Women

¹ University of Wisconsin Comprehensive Cancer Center and Departments of ² Population Health Sciences and ³ Medicine and Family Medicine, University of Wisconsin, Madison, Wisconsin; ⁴ Hospital K, Hanoi, Vietnam; ⁵ Breast Center at Baylor College of Medicine, Houston, Texas; and ⁶ Fred Hutchinson Cancer Research Center, Seattle, Washington

Requests for reprints: Hazel B. Nichols, University of Wisconsin Comprehensive Cancer Center, Madison, WI. Phone: 608-263-7890; Fax: 608-265-5330. E-mail: hbnichols{at}wisc.edu

We evaluated associations between reproductive and lifestyle risk factors with breast cancer tumor marker status in a case-control study. Cases were premenopausal women living in Vietnam and China who were eligible for a clinical trial of oophorectomy and tamoxifen as treatment for breast cancer (n = 682). Controls were nonrelative hospital visitors, matched on age to the cases (n = 649). Immunohistochemical analysis was used to identify the presence of estrogen receptor (ER) and progesterone receptor and the overexpression of HER-2/neu oncogene. Odds ratios (OR) and 95% confidence intervals (95% CI) were estimated using unconditional logistic regression, adjusted for known confounders. Overall, 280 (61%) tumor samples were ER positive and 176 (38%) were ER negative. HER-2/neu overexpression was detected in 161 (35%) samples, whereas 286 (26%) samples were HER-2/neu negative. We observed an inverse trend between increasing parity and decreasing breast cancer risk (P = 0.002). Women ages 25 years at first birth had increased breast cancer risk compared with women ages <25 years at first birth (OR, 1.53; 95% CI, 1.20-1.95). Women who consumed alcohol had increased risk of breast cancer compared with women who did not (OR,1.85; 95% CI, 1.32-2.61). Compared with controls, OR estimates for breast cancer by parity and age at first birth were significantly associated with ER and/or HER-2/neu tumor status by Wald test (P < 0.05). Family history, age at menarche, cumulative lactation, body mass index, and education were not significantly related to breast cancer risk. Our findings support the hypothesis that some breast cancer risk factors differ by ER and HER-2/neu tumor marker subtypes.

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