Teaching Case

A 57-year-old asymptomatic black man presented with palpable mass in his right breast. At physical examination, a painless, firm and fixed to the pectoral fascia nodule was found in the inner quadrant of his right breast. No axillary nodes were palpable.

Mediolateral oblique mammogram showed a round mass with spiculated and indistinct borders, without distortion of the surrounding parenchyma or associated microcalcifications that correspond to the palpable mass located in the inner quadrant of the right breast. No skin thickening or retraction was seen. No axillary adenopathies were found (Figure 1).
Ultrasound was concordant and revealed a round, hypoechoic and inhomogeneous solid mass, with partially indistinct borders and 9mm in diameter, touching the pectoral fascia, which correspond in size and location to the lesion palpable at physical examination and seen on mammogram (Figure 2).
Using an automated 14-gauge needle, an ultrasound guided core biopsy was performed because of the clinical and imagiologic suspicion of malignancy (Figure 3).
Histological and immunohistochemical analysis led to a correct diagnosis of a benign tumor (Figure 4).

Granular cell tumour was first described in 1926 as a myoblastoma because of the histological resemblance of the tumour to striated muscle. Current evidence suggests a neural origin from Schwann cells and the term granular cell tumour has been widely accepted [1].
Occurring approximately once for each 1000 primary breast carcinomas, it is a rare neoplasm, typically solitary and smaller than 3 cm that occurs in many sites throughout the body. Common locations are the skin, muscles and internal organs, particularly the upper aerodigestive tract [1, 2]. Approximately 6% of them occur in the breast. Although these tumours are almost invariably benign, rare malignant examples have been reported.

Patients are usually middle-aged, black, premenopausal women, although rare examples have been reported in males.
Clinically, granular cell tumour presentation may be similar to that of breast carcinoma. Patients usually complain of a painless breast mass, often located in the upper inner quadrant. On palpation the tumour can be firm, with rounded, slightly irregular borders, movable or fixed to the pectoral fascia. Retraction of the overlying skin may occur when the tumour is superficial [1, 2, 3].

On mammography, granular cell tumour can be well circumscribed or spiculated, appearing as a new mass or known lesion with recent enlargement mimicking a carcinoma. On ultrasound it can demonstrate a prominent acoustic shadowing, also suggesting a malignant tumour. Microscopic examination is therefore required to establish the correct diagnosis. Automated core needles in 18- to 14- gauge are commonly used to biopsy masses with ultrasound, although the types of biopsy needles used for specific breast lesions and guidance methods vary around the world [4].
Microscopically, nests of cells showing a wide granular cytoplasm and small round nuclei characterise granular cell tumour. The diagnosis can be established by immunohistochemistry or demonstrating electrodense granular structures corresponding to secondary lysosomes [5].
Breast MRI should be performed if the pathology results show malignancy [6].

Recommended management is surgical, with local excision as wide as possible to avoid tumour growth and to prevent its recurrence. Although these tumours are mostly benign and therefore potentially cured, local recurrence has been reported after partial excision and rare cases of malignant granular cell tumour with metastases are known [2, 3].

Granular cell tumour of the breast in a male is a rare condition, in which clinical and imaging features may mimic breast carcinoma. The final diagnosis is possible by performing pathological analysis, which prevent unnecessary radical surgical procedures.