Alcohol's Breast Cancer Risk Traced to Subtypes

(MedPage Today) -- Women who averaged one alcoholic drink a day had almost double the risk of hormone-sensitive breast cancer of nondrinkers, data from the Women's Health Initiative (WHI) showed.

Alcohol consumption had a significant association with invasive breast cancer overall, invasive lobular carcinoma, and hormone receptor-positive tumors (P≤0.022), but the risk of receptor-negative breast cancer was unaffected.

The analysis, reported online in the Journal of the National Cancer Institute, also showed that the association between alcohol and hormone-sensitive breast cancer applied only to lobular invasive breast cancer and not to ductal invasive cancer.

The findings suggest that hormone-sensitive and insensitive breast cancer arise through different etiologic pathways, according to the researchers.

"These findings highlight the importance of incorporating breast cancer subtype information in etiologic studies of the disease," Christopher I. Li, MD, PhD, of the Fred Hutchinson Cancer Research Center in Seattle, and co-authors wrote in conclusion.

Although the link between alcohol and breast cancer is well known, they added, "this study suggests that alcohol primarily increases risk of lobular and hormone receptor-positive breast cancer."

The study is not the first to show that alcohol consumption increases the risk of hormone receptor-positive breast cancer. A meta-analysis of 20 studies showed a 12% increase in the risk of estrogen receptor-positive breast cancer per 10 g of alcohol consumption, whereas the risk of receptor-negative breast cancer increased by only 4% (Int J Cancer 2008; 122: 1832-1841).

But, the authors noted, relatively little information exists about the association between alcohol consumption and different histologic types of breast cancer. The WHI database provided the opportunity to examine the association in a large population of women.

The investigators assessed the relationship between self-reported alcohol consumption and postmenopausal breast cancer risk in 87,724 participants in the WHI observational study conducted from 1993 through 1998. The participants were classified as never drinkers (<12 alcoholic drinks of any type in their lifetime), former drinkers, and current drinkers.

Current drinkers were grouped into six categories based on weekly alcohol consumption, ranging from less than 0.5 drinks a week to 14 or more. The investigators further characterized consumption by type of alcohol (beer, wine, and liquor).

During follow-up through Sept. 15, 2005, 2,944 patients were diagnosed with invasive breast cancer. In a multivariable analysis, increasing alcohol consumption had a significant association with overall risk (P=0.004).

The association remained statistically significant in an analysis that considered invasive breast cancer overall, invasive lobular carcinoma, and hormone receptor-positive tumors

Further analysis showed that alcohol's impact on cancer risk was greatest for hormone receptor-positive lobular carcinoma, resulting in a hazard ratio of 1.82.

Alcohol consumption did not influence the risk of hormone receptor-positive ductal carcinoma.

Rates of hormone receptor-positive lobular carcinoma in never drinkers and current drinkers were 5.2 and 8.5 per 10,000 person-years, respectively. Corresponding rates for hormone receptor-positive ductal carcinoma were 15.2 and 17.9 per 10,000 person-years.

Use of unopposed estrogen or combined hormonal therapy did not affect the risk of hormone receptor-positive lobular or ductal carcinoma.

The authors acknowledged the primary limitation of their study as the lack of data on changes in alcohol consumption over time, as consumption was assessed at a single point in time.

The authors reported that they had no relevant disclosures.

Primary source: Journal of the National Cancer Institute Source reference: Li CI, et al "Alcohol consumption and risk of postmenopausal breast cancer by subtype: the Women's Health Initiative observational study" J Natl Cancer Inst 2010; DOI: 10.1093/jnci/djq316.