Neurofibromas arising within the breast parenchyma are extremely rare, and only three cases have been reported in which the neurofibroma was clearly identifiable on imaging as a neurofibroma within the mammary tissue [6,7,8]. Of these three case reports, two had tumors locating closer to the chest wall than within the breast [6, 7]. This is one of the few reports in which the rare intramammary tumor could clearly be identified within the breast gland by imaging studies. No difference between males and females in the incidence of this disease is observed. The age of affected patients is reported to range widely from 4 to 77 years [9, 10], and our patient is the oldest. Mammography of this condition shows a round or oval well-defined mass. Ultrasound examination reveals a well-defined round lesion, which can be either hypoechoic or anechoic with posterior acoustic enhancement [6]. Regarding the findings with Color Doppler, half of the patients were blood flow-rich, and half were hypovascular. However, in our patient, ultrasound images showed internal heterogeneity in one part of the mass. This was because the mass also contained adenosis. We searched PubMed for the words “neurofibroma” “breast” “adenosis” and found no precedent. The reason for adenosis accompanying the neurofibroma is unknown. In addition, the association between the presence of adenosis inside the tumor and its growth in a short period of time is unknown.

In case reports of breast neurofibroma, tumor resection was preferred and the patient was treated with tumor resection. In general, solitary neurofibromas are associated with a low local recurrence rate if completely excised [12]. There are few reports of long-term follow-up of breast neurofibromas, and the risk of malignant transformation is unknown. In contrast, the risk of malignant transformation of a neurofibroma in patients with NF1 is approximately 4.6% [11]. Further case accumulation of breast neurofibroma in non-neurofibromatosis is necessary. A case has been reported in which the tumor gradually grew to 2200 g in size after two years of follow-up [13]. The only reference describing the rate of enlargement was this single case report, which did not describe the size of the tumor at the time of initial diagnosis. In the present case, the volume increased 3.5-fold in approximately 2 months after the patient became aware of the breast mass. Most benign tumors such as fibroadenoma do not change in the short time. In this case, needle biopsy is mainly spindle cell proliferation, not typical fibroadenoma, which is the reason for the short follow up. If a benign tumor with spindle cell lesion is found to be enlarged, we recommend tumor resection.

In addition, diagnosis breast needle biopsy is often difficult because of the small sample amount and wide range of differential diagnoses. The differential diagnosis of a neurofibroma includes neuroma, schwannoma, and bland non-nerve sheath spindle cell lesions [14]. Microscopically, a typical neurofibroma consists of bland spindle cells and fibroblasts dispersed in loose collagen fibers that condense to form a shredded carrot-like appearance. Neurofibromas lack nuclear palisading and Verocay bodies, alternating Antoni A and Antoni B areas, and prominent hyalinized vessels. By immunohistochemistry, a proportion of spindled cells express S100 and SOX10, CD34 stains a subset of stromal cells, but cytokeratins, ER, actin, and desmin are negative.