Pigmented Dermatofibrosarcoma Protuberans and Blue Naevi with Similar Dermoscopy: A Case Report

A 71-year-old Japanese woman was referred to our department for evaluation of 3 pigmented lesions on her left buttock. She had been aware of the lesions for a few months. Physical examination revealed 3 blue nodules, approximately 7, 8 and 4 mm in diameter, located on the left buttock (Fig. 1a). Dermoscopic examination revealed a homogeneous blue pigmentation with whitish-veil structures in each of the 3 lesions (Fig. 1b). However, the colour of the upper lesion was paler than that of the other lesions. Based on these findings, we suspected that these were blue naevi. The middle lesion was resected under local anaesthesia. Histopathological examination revealed diffuse proliferation of spindle cells containing melanin granules in the lower dermis (Fig. 1c). A diagnosis of cellular blue naevus was made. The remaining 2 lesions were not resected, and a wait-and-see approach was taken. After 2 years, the patient became concerned about the remaining 2 lesions, and returned to our department for treatment. The 2 blue nodules were slightly increased in size on the left upper and lower buttocks (Fig. Sla1). There was no change in dermoscopic features compared with those seen 2 years previously (Fig. Slb1). The 2 lesions were resected under local anaesthesia. The diagnosis of the lower small lesion was blue naevus. Histopathologically, the other lesion on the upper buttock showed massive proliferation of atypical spindle-shaped cells arranged in a storiform pattern from the lower dermis to the subcutaneous adipose tissue. In addition, there were scattered dendritic cells containing granular melanin pigments (Fig. Slc1, Sld1). Immunohistochemically, the spindle tumour cells were positive for CD34 (Fig. S1e1), but negative for S-100 protein, while dendritic cells were only positive for S-100 protein (not shown). A diagnosis of Bednar tumour (pigmented dermatofibrosarcoma) was made. An additional extensive resection with a 3-cm tumour Pigmented Dermatofibrosarcoma Protuberans and Blue Naevi with Similar Dermoscopy: A Case Report