Investigation of the significance of population-based breast cancer screening among women aged under 40 years.

Background: Owing to low incidence rates, population-based breast cancer screening is not recommended by many municipalities in Japan for women aged < 40 years. To evaluate the usefulness of screening in women aged < 40 years, we investigated the results of population-based breast cancer screening among young women performed in the Ibaraki Prefecture.
Methods: Data regarding histological characteristics, recall rates, cancer detection rates, positive predictive values, tumor categories, and status of lymph node metastases were obtained from population-based screening data from Ibaraki Health Service Association Institute. The "number needing to be screened" (NNS) was determined; using Pearson's chi-squared test, these data were compared between women aged < 40 years and > 40 years.
Results: The data of 428,560 women were evaluated. Cancer detection rates were significantly lower and the NNS and proportion of women with tumor category T2 or higher was significantly increased in women aged < 40 years than in those aged > 40 years (0.06% vs. 0.21%, 1505 vs. 281-439, and 28.9% vs. 6.3%, respectively; all, p < 0.05). The proportion of early-stage cancers was lower in women aged < 40 years than in those > 40 years, but this was not significant.
Conclusions: These results suggest that population-based breast cancer screening should not be recommended for women aged < 40 years. To reduce the breast cancer-related mortality rate in young women and ensure efficient use of limited medical resources in Japan, a more efficient surveillance system, based on genetic propensity and family history, needs to be established.