An Unusual Granular Cell Tumour of the Buttock and a Review of Granular Cell Tumours

Granular cell tumours, first described by Abrikossoff in 1926, are known to occur in skin, connective tissue, breast, gastrointestinal and genital tracts. While they are rare, they are more common in people of African descent and show a slight female preponderance, usually presenting as solitary and painless masses. Less than 10% of occurrences are multiple, and fewer than 3% of tumours behave in a malignant fashion. The mean age, at presentation, is 40–60 years. We report a case of granular cell tumour in a young white male presenting with a painful soft tissue tumour in his buttock. The presentation is unusual because of the age, patient demographic, body site, and clinical presentation. The clinical and histological aspects are reviewed in the context of this clinical case and the associated literature. 1. Background Granular cell tumours were first described by Abrikossoff in 1926 and are known to occur in skin, connective tissue, breast tissue, and gastrointestinal and genital tracts—with the head and neck being the most common regions. The tongue is the most common site in the head and neck [1]. Granular cell tumours are rare; some authors have suggested that they make up around 0.5% of all soft tissue tumours [2]. Frequent locations are the tongue (40%), breast (15%), respiratory tract (10%), and oesophagus (2%) [3]. The tumours can be multicentric (5% to 14% of cases) [3]. These tumours have a higher incidence amongst women and a greater prevalence amongst people of African descent. There has been one case report of a mother and son, both of whom presented in childhood with multiple granular cell tumours [4]. While the origins of granular cell tumours are often debated, Abrikossoff originally postulated a myogenic origin and termed this a “myoblastoma.” These tumours are now considered to be neoplasms of neural origin, as evidenced by immunohistochemical studies [5]. Diffuse S-100 positivity is present in nearly every case. S-100 is a calcium binding protein expressed in nerve tissue, melanocytes, adipocytes, and myoepithelial cells. Dermal nonneural granular cell tumours may be a different entity [6]. It is difficult to make a diagnosis of malignancy in these tumours based on the histological appearance. Tumours that do metastasize tend to show cellular pleomorphism, mitotic activity, and spindling. Size greater than 5？cm, rapid growth rate, or invasion of adjacent structures is more likely to suggest malignancy [7]. Most granular cell tumours are benign, with a self-limiting growth pattern. When they metastasize, the most common sites are