Breast fibroadenoma is the most common fibroepithelial tumor comprising both epithelial and mesenchymal components. Although ductal epithelial hyperplasia or metaplasia is common in fibroadenomas, malignant transformation in fibroadenoma is very rare. Cheatle in 1931 first reported carcinoma within fibroadenoma was first reported; subsequently, people gradually increased their understanding, and different types of intrafibroadenoma carcinoma were reported successively [1,2,7] . The types of intrafibroadenoma carcinoma include lobular carcinoma in situ, ductal carcinoma in situ, and invasive breast cancer. This study focused on the clinical features, pathological characteristics, differential diagnosis, therapy, and prognosis of lobular carcinoma in situ within fibroadenoma.
Fibroadenomas are often painless, isolated, and slow-growing nodules. However, breast carcinoma within a fibroadenoma may be accompanied by a rapid increase in mass in a short period. The radiology showed clear nodules with occasional calcification. Studies have shown that one should be vigilant against the occurrence of tumors with fuzzy edges or microcalcifications. Many studies have reported that fibroadenoma is the most common type of benign tumor in women aged less than 35 years. In addition, older age is considered a riks transformation of factor for malignant fibroadenoma . In fact, no clear difference exists between intrafibroadenoma carcinoma and fibroadenoma in terms of clinical and radiological manifestations. Malignancy is rarely suspected even during gross examination, and the final diagnosis depends on pathology. As reported in this case, the patient was a 38-year-old relatively young woman who had no special clinical and imaging findings but was diagnosed with lobular carcinoma in situ within fibroadenoma. Therefore, we must be careful of not only the malignant transformation of old or suddenly enlarged fibroadenoma, especially lobular carcinoma in situ, but also young and symptomatic fibroadenoma.
Breast fibroadenoma is a common benign fibrous and epithelial tumor. The latest edition of the World Health Organization of the breast divides fibroadenoma into four types, namely classic type, juvenile type, complex type, and cell-rich type . The risk of breast cancer in complex fibroadenoma is increased compared with that in other types of fibroadenoma  . The fibroadenoma mainly presents a growth pattern in and around the tube, with no dysplasia of interstitial cells. Epithelial components are often accompanied by common ductal hyperplasia, myoepithelial hyperplasia, sclerosing adenopathy, fibrocystic degeneration, or apocrine metaplasia. Moreover, atypical ductal or lobular hyperplasia, ductal or lobular carcinoma in situ, and invasive carcinoma are occasionally seen in fibroadenoma.
Carcinomas within fibroadenoma refer to the cancerous transformation of epithelial components into fibroadenoma; the cancerous tissue is limited to fibroadenoma or accompanied by small infiltration. Carcinomas within fibroadenoma include lobular carcinoma in situ, ductal carcinoma, and invasive carcinoma. The literature reports showed that the occurrence of lobular carcinoma in situ was the most common. Other types of cancer, such as mucus carcinoma, metaplastic carcinoma, and adenoid cystic carcinoma, are rarely reported. Lobular carcinoma within fibroadenoma needs to be differentiated from the following diseases. (1) Ductal carcinoma in situ within fibroadenoma: It has uniformly packed cells in the lumen, but lobular carcinoma in situ loses adhesion and is negative for E-caherin. (2) Common ductal epithelial hyperplasia in fibroadenoma: It also involves the terminal ductal lobular unit, but the cells are disorderly or with the flow-like arrangement, and cell size is inconsistent. In addition, immunohistochemical markers show a mixed phenotype of the myoepithelial and glandular epithelium; Estrogen receptor (ER) and progesterone receptor (PR) are expressed unevenly. (3) Carcinoma within phyllode tumors: Sometimes, it is difficult to distinguish between fibroadenomas and phyllode tumors. The latter often forms distinct phyllode-like structures; mesenchymal spindle cells are also significantly proliferated and even atypical. (4) Lobular carcinoma: It should be differentiated from invasive carcinoma in fibroadenoma. The main body of invasive cancer is often absent in fibroadenoma and infiltrates into fibroadenoma. Cell atypia of the invasive cancer is obvious, mitosis is easily seen, and negative for P63.
Managing cancer in fibroadenomas often adopts corresponding programs according to the type, scope, and hormone receptors of the cancer. Simple tumor resection is recommended for lobular carcinoma in situ within fibroadenoma [10,11]. However, simple mastectomy should be considered when the tumor is large, multifocal, or in the center of the breast. Compared with the same type of breast cancer, fibroepithelial intratumoral cancer is less biologically aggressive. This may be related to the envelope of fibroepithelial tumors, restricting cancer growth , but further confirmation is needed. When a fibroadenoma suddenly enlarges or is found to be accompanied by calcification on radiography, a fine-needle needle biopsy should be performed to determine the nature of the mass.