Syringocystadenocarcinoma papilliferum in a linear nevus verrucosus.

Syringocystadenocarcinoma papilliferum (SCACP), the malignant counterpart of syringocystadenoma papilliferum (SCAP), is a rare form of adenocarcinoma of the skin. Only 11 well-documented case reports of SCACP have been published so far. An 83-year-old woman with a linear nevus verrucosus (LNV) on her right arm had a history of a nodule arising within this nevus that was diagnosed as SCAP by skin biopsy 7 years earlier. Since then, the nodule had enlarged gradually and formed an exophytic tumor with a moist surface, measuring 3 × 2.5 cm. The tumor was excised and studied by histologic examination. Although histologically the overall architecture of the tumor still resembled SCAP, transition to SCACP was obvious by the presence of areas of cytonuclear atypia, increased proliferative activity and infiltrative growth. The edges of the excised ellipse flanking the tumor showed typical microscopic features of LNV, but no organoid components of nevus sebaceus (NS).We report the 12th case of SCACP, the first case of SCACP on the arm and the first case of SCACP arising from pre-existing SCAP, in what appeared to be an epidermal nevus.