Teaching Case

A 40-year-old woman, asymptomatic, revealed, on routine physical examination, an asymmetric stiff area in the upper outer quadrant of the left breast. The patient was referred to our imaging department for further evaluation.

Ultrasound showed a solid nodular lesion on upper-outer quadrant of the left breast, hypoechoic, with regular margins and well-defined, measuring around 13 mm of axial diameter (Fig 1). Elastographic evaluation of this lesion was also performed demonstrating features suggestive of malignancy such as less compressibility and more stiffness comparing to the surrounding tissue (Fig 2a). The area of highest shear-wave velocity in the elastogram was 7.9, increasing the malignancy suspicion, comparing with the adjacent tissue this value was 0,88 (Fig. 2b). Axillary adenopathies were not identified. On mammography, this lesion was a round mass well-defined with irregular borders, without distortion of the surrounding parenchyma or microcalcifications. No skin thickening or retraction was seen (Fig 3). The patient was then submitted to core biopsy using a 16 gauge needle guided by ultrasound.

Granular cell tumour is a rare tumour that affect of the breast in 5-8%, usually benign tumour which is possibly of neural origin (1).
They tend to occur at a younger age, more commonly in pre-menopausal black women (2).
Clinically they can mimic malign tumours because of their fibrous consistency and their hardness, thus presenting as a palpable mass, but painless (2). Usually less than 30mm in size, and are most frequently found in the upper inner quadrant (supraclavicular nerve territory) followed by the axillary tail (3).
On mammography, these tumours can present as a well-defined or irregular/spiculated lesions. Microcalcifications are not usually a feature.
The same variability can be shown on ultrasound, this tumour can appear as a solid, hypoechoic, ill-defined mass, associated with a posterior shadowing, or as a well-circumscribed oval mass, associated with a posterior enhancement and hyper-echoic halo depending on the extent of infiltration and degree of reactive fibrosis (4). The tumour pathological properties, such as its fibrous consistency and infiltrative growth pattern, are responsible for the malignant imaging appearance and the differential diagnosis is made mainly with breast carcinoma. Therefore, the final diagnosis is only possible by histological assessment (5). Cells with eosinophilic granules with abundant cytoplasm are characteristic. There is no evidence of nuclear pleomorphism, multinucleated cells or mitosis. It is indicative of this tumour if DPAS is positive, nuclear and cytoplasmic positivity for S100, cytoplasmic staining for CD68, due to their lysososmal activity and negative reaction for cytokeratins, HMB45 and MelanA (3)
The therapeutic procedure is complete surgical excision to avoid tumour recurrence (it has been reported in about 1%) (5).
In this case, the biopsy revealed a lesion suggestive of granular cells infiltrating. The patient had a conservative surgery. The examination showed a neoplasia containing large eosinophilic and granular cytoplasm with poorly defined limits and a small round central nucleus without atypia. Mitotic activity is not observed. Exicision margins were free from neoplasia. S100 protein diffusely positive, with strong co-expression for CD68 antibody. Negativity for pankeratin AE1 / AE3 and CAM 5.2, negativity for P63 myoepithelial marker. Negativity for estrogen receptor.
Thus, the final diagnostic of a benign granular cell tumour of the breast was made.