Natural history of fibroadenomas based on the correlation between size and patient age

Several recent studies have reported that most fibroadenomas remain static or regress when they are managed conservatively; however, no such studies have evaluated the breast disorder in Japanese women. To understand the natural history of fibroadenomas in Japanese women, we examined the correlation between the sizes of the fibroadenomas and the women's age.

Fifty-eight consecutive patients (age range, 17-51 years; mean, 33.9 years) with histologically confirmed fibroadenoma were enrolled in this study. The sizes of the excised fibroadenomas were analyzed in relation to the women's ages.

The fibroadenomas decreased significantly in size (Y, mm) with patient age (X, years) (P = 0.0012) according the equation Y = -0.340X + 27.0 (95% confidence limits for the slope, -0.139 to -0.540). From this equation, the mean sizes of the fibroadenoma in women aged 20, 30 and 40 years were expected to be 20.2 mm (95% confidence interval, 16.2-24.2 mm), 16.8 mm (95% confidence interval, 10.8-22.8 mm) and 13.4 mm (95% confidence interval, 5.4-21.4 mm), respectively. The mean annual decrease in the size of the fibroadenomas was 0.340 mm.

Our results indicate that in Japanese women fibroadenomas increase in size more frequently in younger than in older women. Moreover, it is speculated that most fibroadenomas might stop growing when they reach an approximate maximum diameter of 20 mm, after which time they might remain static or regress.