Lobular involution, mammographic breast density associated with breast cancer incidence

Issue: November 25, 2010

Results of a nested cohort study showed an inverse relation between age-related atrophy of breast lobules. The same results showed that women with dense breasts were at increased risk for breast cancer.

There were 9,376 women enrolled in the Mayo Benign Breast Disease study from January 1967 to December 1997. A subset of 2,666 women who were diagnosed with benign breast disease from 1985 to 1991 and had a mammogram within 6 months of diagnosis were selected for the study. After a mean duration of 13.3 years, 6.5% of women in the nested cohort developed breast cancer.

Mean age at biopsy was 54.7 years, and there was an increased risk for breast cancer in women who were aged 55 years or older (HR=2.07; 95% CI, 1.37-3.14), had atypical hyperplasia (HR=3.69; 95% CI, 2.30-5.91) and who had a family history of breast cancer (HR=1.80; 95% CI, 1.24-2.61).

Overall, 24% of women showed complete involution, 13.5% showed no involution and 62.5% showed partial involution. Most women in the cohort (65%) had dense breasts, and 60.7% of women who had no involution also had extremely dense breasts.

Age-adjusted analyses showed that lobular involution (P<.001) and breast density (P=.002) were associated with breast cancer risk. Adjusting for confounders, including age, benign breast disease histology and family history, multivariate analyses showed that the association held for both lobular involution (P=.002) and mammographic breast density (P=.018).

Compared with women who had complete involution, women with no involution (HR=2.62; 95% CI, 1.39-4.94) or partial involution (HR=1.61; 95% CI, 1.03-2.53) had increased risk for breast cancer.

Researchers said women with dense breasts showed statistically significantly increased risk for breast cancer compared with women with non-dense breasts. Further, women with dense breasts were at higher risk compared with women who had non-dense breasts within each category of involution.

Within each category of mammographic breast density, women with no involution were at higher risk compared with those who had complete involution.

Age-adjusted analysis showed that women with no lobular involution and dense breasts were at increased risk compared with women with complete involution and non-dense breasts (HR=5.14; 95% CI, 2.18-12.1). Adjusting for factors such as age and family history slightly reduced the risk association (HR=4.08; 95% CI, 1.72-9.68).

“These findings suggest that visual representations of the architecture of the breast on both microscopic (ie, involution) and macroscopic (ie, mammographic breast density) levels potentially represent clinically useful intermediate endpoints,” they wrote in an accompanying editorial.

For more information:

Ghosh K. J Natl Cancer Inst. 2010;doi:10.1093/jnci/djq414.

Gierach GL. J Natl Cancer Inst. 2010;doi:10.1093/jnci/djq433.