Is tubular apocrine adenoma a distinct clinical entity?

A 75-year-old Japanese man developed a tubular apocrine adenoma (TAA) (tubulopapillary hidradenoma with apocrine differentiation, a rare skin tumor), within a long-standing organoid nevus on the parietal area of his scalp. Histologically, the tumor consisted of dilated ductlike areas with some atypism and apocrine glandlike areas surrounded by myoepithelial cells. The superficial part of the tumor was connected to the epidermis and showed some of the characteristics of syringocystadenoma papilliferum (SCAP). The close relationship between TAA, SCAP, and papillary eccrine adenoma (PEA) is discussed. According to 19 reported cases of TAA, SCAP might occur together with TAA when they are preceded by an organoid nevus, and they might represent a spectrum of disease. Although TAA and PEA may represent another spectrum (designated as tubulopapillary hidradenoma), the relationship to SCAP should be considered in understanding and diagnosing an intermediate case.