Lobular involution protects against breast cancer.(GYNECOLOGY)(Clinical report)

SAN ANTONIO -- Young women with a benign breast biopsy showing complete lobular involution are at below-average risk of future breast cancer, according to a large prospective Mayo Clinic study.

This finding--that lobular involution constitutes a novel protective factor against breast cancer in young women with benign breast disease--is an important advance in the effort to better stratify breast cancer risk in the 1 million American women per year who under go a biopsy showing benign breast disease, Dr. Karthik Ghosh said at the San Antonio Breast Cancer Symposium.

Moreover, the lobular involution findings open the door to new breast cancer chemoprevention strategies. Lobular involution may prove to be a factor that can be modified in order to reduce risk, noted Dr. Ghosh of the Mayo Clinic, Rochester, Minn.

She reported on 4,460 women aged 18-49 years in the Mayo Benign Breast Disease Cohort who underwent excisional breast biopsy for a palpable or mammographic abnormality that proved to be benign breast disease. These young women (average age at biopsy, 39 years) have subsequently been followed for a median of 20 years, during which 7% developed invasive breast cancer.

The initial benign biopsy showed complete lobular involution (defined as a 75% or greater reduction in the number and size of breast duct lobules) in 5% of the 4,460 young women. A total of 34% had no lobular involution at all, whereas 61% had partial lobular involution, in the range of 1%-74%.

In a multivariate analysis, the women with complete lobular involution had a 32% reduction in breast cancer rate compared with the general population, which for purposes of this study came from Iowa SEER (Surveillance, Epidemiology and End Results) registry data of an upper Midwest population that is demographically similar to that of the Mayo Clinic.

Women with partial lobular involution had a 43% greater than expected breast cancer rate during 20 years of follow-up, whereas those with no involution had a 72% increased rate (P = .001).