Since breast fibroadenoma is composed of both breast fibrous tissue and glandular ducts, very few breast fibroadenomas can become sarcomatous, but the incidence is relatively low, 0.07%-0.21%. The time of sarcomatous transformation is not clear, it has been reported that sarcomatous transformation occurs after 14 years of fibroadenoma. Fibroadenoma is often squeezed by fibrous mesenchyme because of the glandular ducts, and the glandular epithelial component is less, and the rate of carcinoma is relatively low, but there is a report of invasive or non-invasive carcinoma originated from fibroadenoma. The cancer rate of fibroadenoma is reported to be 0.049%-0.13% in China and 0.12% in foreign countries, which is very low both in China and foreign countries.