Unusually Large Tumor in a Sydney Rock

An unusually large neoplasm with a volume approximately one-eighth that of the body volume of its host, a Sydney rock oyster (erassostrea commercialis), is described and discussed. As in previously described neoplasms of this type, the surface had deep crypts. Microscopic examination revealed a papillary structure throughout. The villi were composed of stratified or pseudostratified atypical epithelium supported by delicate, almost filamentous cores of connective tissue. The atypical epithelium of the tumor was apparently derived From the mantle epithelium. Mitoses were relatively numerous, and the growth penetrated through musde of the mantle into the ovary. The neoplasm was un associated with any significant inflammatory or desmoplastic reaction. Its large size and invasive property indicated that it belonged to a group of progressively growing neoplasms comparable to neoplasms in vertebrate animals.-J Nat Cancer Inst 46:1079-1084,1971.