Benign mixed tumor of the skin, hypercellular variant: a case report.

A 71-year-old man presented with a slowly growing 2.0x2.0x1.0 cm scalp lesion that was surgically removed. Microscopic examination showed a well-circumscribed dermally located tumor composed of ductal elements lined by double to multiple cell layers of bland cuboidal inner cells and elongated spindled outer cells with areas showing cribriform and solid growth patterns. Some cells showed prominent cytoplasmic clearing. A few mitotic figures are noted ranging from 1-2 mitotic figure/10 hpf. There are also foci of squamous differentiation as well as occasional mature adipocytes. The background stroma was predominantly sclerotic with only small area of myxoid background (confirmed by Hale's colloidal iron). Immunohistochemical studies revealed positive immunoreactivity for EMA, CEA, CD117, HWMK, LWMK, CK7, Androgen receptor and S100 in the ductal (epithelial) cells and positive immunereactivity for calponin, SMA, CK 5/6 and p63 in the myoepithelial component. No immunoreactivity for Brst-2, ER, PR and CK20 was noted. MIB-1 showed mildly increased proliferrative index highlighting 5% of the nuclei. The overall morphology and immunohistochemical profile are that of a benign cutanoues mixed tumor (chondroid syringoma). Given the unusual striking celluarlity, we suggest to subclassify this as a hyper-cellular variant.