Finger soft tissue myoepithelioma: a rare entity

Abstract

We report a case of a cutaneous myoepithelioma in a 69-year-old, right-hand dominant, gentleman with an 18-month history of a progressively, enlarging mass on the volar aspect of his left middle finger over the proximal phalanx. The lesion measured 2 × 2 cm in dimensions (Fig. 1a); there was no associated neurosensory deficit, vascular compromise or involvement of the flexors of the affected finger. The patient underwent pre-operative magnetic resonance imaging (MRI), revealing a lobulated lesion with increased vascularity. It had a predominantly high signal on T1 (Fig. 1b), with no involvement of the flexor synovium or bone. The lesion was given a provisional diagnosis of a giant cell tumour (GCT), but that a vascular anomaly or a synovial sarcoma could not be excluded.Surgical excision of this lesion was performed, with dissection of the lesion off the skin and flexor sheath, preserving the neurovascular bundles (Fig. 1c). The tissue was sent fresh for histology, and the wound was directly closed.The specimen did not have the typical clinical appearance of a GCT, and was diagnosed as a myoepithelioma.Histology revealed an un-encapsulated tumour composed of nests of mildly pleomorphic histiocytoid/plasmacytoid cells within a vascularized myxoid fibrous stroma. The lesion was diagnosed as a myoepithelioma, associated with a low mitotic count of 1 per 10 high power fields and with no necrosis. Foci of squamous associated keratin formation were noted (Fig. 2a), with expression of both low (Fig. 2b) and high (Fig. 2c) molecular weight cytokeratins, vimentin (Fig. 2d) and S100 (Fig. 2e). There was no expression of smooth muscle actin, CD68 (histiocytic marker), vascular markers (CD34), and melanocytic markers (HMB-45 and melan A). The lesion was completely but narrowly excised.Post-surgical recovery was uneventful. A discussion of the diagnosis at a complex hand meeting and with our oncology colleagues reached an overall consensus for long-term follow-up as further surgery would involve significant functional compromise with no role for either chemo/radiotherapy.Cutaneous myoepithelioma (CM) tumours, also known as parachordomas, are rare primary tumours of the soft tissues, 1 proposed to arise from either the eccrine or the apocrine glands. 2 There have been just over 100 cases reported in the literature with only 10 in the hand. 1,3 CMs are typified by a mixed myxoid, chondroid and epithelial histological phenotype with plasmatoid or spindle cell features. 3 Although CMs share similarities with GCTs, the lack of expression of CD68, as is typically seen in the mononuclear fraction of GCTs, 4 was not evident in this case.They are considered benign tumours yet are associated with high rates of local recurrence of close to 20%, 3,5 but are distinct from the more aggressive myoepithelial carcinomas, with higher rates of metastasis and increased cellular atypia. 3 With regard to metastasis, a review by Clark et al. 1 of 22 cases of upper limb CMs revealed 10 cases in the hand. There was only one case in the forearm that h...