Study links heavier drinking to changes in normal breast tissue tied to cancer biology

A study in the British Journal of Cancer has found a possible link between alcohol use and changes in normal breast tissue that researchers say could help explain how drinking affects breast cancer risk.

The research looked at 683 women in the Nurses’ Health Study II who had biopsy-confirmed benign breast disease and no cancer diagnosis. Investigators examined whether recent drinking and long-term average alcohol intake were associated with the expression of several stromal markers in benign breast biopsy samples. Stromal tissue is the connective tissue that surrounds breast structures and plays an active role in how tissue behaves.

The main signal in the study involved tenascin-C, or TNC, a marker tied to fibroblast activation and remodeling of the extracellular matrix. In multivariate analysis, cumulative average alcohol intake showed a suggestive positive association with TNC expression, with a beta coefficient of 0.59 for each additional 11 grams of alcohol per day, roughly one drink, and a p value of 0.06. That result did not meet the conventional threshold for statistical significance, but the authors said it pointed to a possible relationship that should be tested further.

When researchers looked at heavier long-term drinking, they found that women consuming at least 22 grams of alcohol per day, or about two drinks daily, had higher TNC expression than non-drinkers, with a beta coefficient of 2.50 and a 95% confidence interval of 0.20 to 4.80. By contrast, alcohol intake was not associated with four other stromal markers studied: α-SMA, FAP, s100a6 and MMP14.

The authors said the findings suggest alcohol may be linked to increased activation of normal stromal fibroblasts in histologically normal breast tissue. Fibroblasts are abundant cells in breast stroma and are involved in maintaining connective tissue and remodeling the extracellular matrix. In cancer research, activated fibroblasts have drawn attention because they can shape the tumor environment and have been associated with more aggressive disease.

The study adds a new layer to a large body of evidence connecting alcohol and breast cancer. The paper notes that women who consume 15 to 30 grams of alcohol per day, about one to two drinks, face a 10% to 40% higher risk of breast cancer than non-drinkers in prior research, and that each additional daily drink has been linked to about a 7% increase in risk. It also cites the International Agency for Research on Cancer classification of alcohol as a Group 1 carcinogen and notes that the U.S. Surgeon General has described the relationship between alcohol and breast cancer as causal.

Researchers have proposed several biological pathways for that risk. Ethanol is metabolized into acetaldehyde, which can damage DNA and interfere with repair. Alcohol has also been linked to oxidative stress, inflammation and changes in estrogen metabolism. The new study explored whether another pathway may involve changes in stromal tissue before cancer develops.

The women in the analysis were part of a long-running U.S. cohort established in 1989 that enrolled 116,430 female registered nurses ages 25 to 42 at baseline. For this project, investigators focused on participants with incident benign breast disease confirmed by biopsy and available tissue samples. The average age at biopsy was 44, with an age range of 27 to 63. Most participants, 81.3%, were premenopausal at the time of biopsy. In terms of pathology, 65.3% had proliferative disease without atypia, 26.2% had nonproliferative disease and 8.5% had proliferative disease with atypia.

Alcohol intake was measured through repeated food frequency questionnaires that asked about wine, beer and liquor consumption over the previous year. Standard drink definitions used by the study were one can or bottle of beer, a 4-ounce glass of wine or one shot of liquor. Total alcohol intake was converted into grams per day using beverage-specific ethanol content estimates. Recent intake was based on the questionnaire closest to the biopsy date, while cumulative average intake reflected all available questionnaires before biopsy. For most participants, that long-term measure drew on four or more questionnaires.

In this sample, 22% of women were non-drinkers, 70% consumed less than one drink per day on average and 8% consumed at least one drink per day. Tissue samples were analyzed using multiplex immunofluorescence on microarrays built from normal terminal duct-lobular units identified within benign biopsy specimens. Marker expression was quantified as the share of stromal cells staining positive for each marker.

The authors stressed that their findings should be interpreted cautiously. The association with continuous cumulative alcohol intake and TNC was described as borderline significant, and categorical analyses did not show broad associations across all drinking levels or across all markers. In an exploratory analysis limited to premenopausal women, no significant association was found for cumulative alcohol intake and TNC, which the researchers said may reflect reduced statistical power because of the smaller subgroup size.

They also noted that this was the first study to test alcohol use against several stromal markers in cancer-free women’s benign breast tissue, but not a study that can prove cause and effect on its own. Future work will be needed to confirm whether alcohol exposure is truly linked to TNC expression and whether that change plays a role in early breast carcinogenesis.

For beverage producers and sellers, the findings matter because health evidence around alcohol continues to shape public policy debates, warning labels, consumer behavior and broader perceptions of wine, beer and spirits. If future studies confirm this kind of tissue-level effect, it could add to pressure for stricter public health messaging around drinking and cancer risk.