Olfactory neuroblastoma associated with extensive "in situ" lesion and aberrant glandular and rhabdomyosarcomatous differentiation.

A case of olfactory neuroblastoma (ONB) associated with extensive intraepithelial neoplastic proliferation, evidenced by an "in situ" lesion, in the overlying olfactory epithelium and aberrant glandular and rhabdomyosarcomatous differentiation is reported. The tumor was a polypoid lesion that involved the upper nasal cavity and ethmoid sinus of a 63-year-old woman and consisted of an ONB surrounded by and mixed with a proliferative lesion of rhabdomyoblastic cells, consistent with an embryonal rhabdomyosarcoma. A few small foci of tubular glands with mucus-producing cells were also observed. In the olfactory epithelium covering the polypoid lesion, a nested or band-like arrangement of primitive-appearing small cells was found, and the tumor cells were immunoreactive for epithelial cell adhesion molecule (detected with Ber-EP4) and low-molecular weight cytokeratin (detected with CAM5.2) but not for synaptophysin or calretinin. The intraepithelial lesion was contiguous with the subepithelial cell nests of ONB and appeared to invade the subjacent stroma and show transition to ONB, and some tumor cell nests of ONB also contained small aggregates of similar primitive-appearing cells. The intraepithelial growth was considered to represent a preinvasive precursor lesion of ONB. Previous descriptions of an "in situ" lesion in ONB are limited. The aberrant glandular and rhabdomyosarcomatous differentiation noted in this case is also an exceptionally rare phenomenon of ONB.