The increasing prevalence of benign proliferative breast lesions in Japanese women.

BACKGROUND: Although the increasing incidence of breast cancer in Japan has been well-documented, the possibility that there also has been an increase in the frequency of benign proliferative breast disease in Japanese women has not been previously studied.

METHODS: The authors compared the histologic findings in a series of 266 consecutive benign breast biopsy specimens from 1974 to 1975 (Group I) to those in a series of 266 similar biopsy specimens accessioned at the same institution in Japan one decade later (i.e., 1984 to 1985; Group II). The extent of sampling was similar in both groups. The specimens were categorized as showing nonproliferative lesions, proliferative lesions without atypia, or atypical hyperplasia using the criteria of Dupont and Page.

RESULTS: Proliferative lesions without atypia were significantly more common in biopsy specimens from Group II than those from Group I (16.2% versus 9%; P = 0.01). Although atypical hyperplasias were twice as common in Group II as in Group I, these lesions were uncommon in both groups (2% in Group II versus 1% in Group I, p = NS). The differences in pathologic findings between the two groups were most evident in younger women. For patients younger than 40 years of age, the prevalence of proliferative lesions (with or without atypia) was 18% for Group II and 6% for Group I (P = 0.003). For patients 40 years of age or older, proliferative lesions were seen in 17% of patients in Group II and 13% in Group I (P value, not significant).

CONCLUSIONS: The frequency of benign proliferative breast lesions in Japanese women, particularly among women younger than 40 years of age, is increasing. These observations are consistent with the results of previous studies in North America that have demonstrated a relationship between benign proliferative breast lesions and the development of breast cancer.