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An unusual lesion observed in the right mantle of an oyster, Crassostrea virginica [see Couch: Nat. Cancer Inst. Monogr. 31: 557–562, 1969], resembles certain reticulum sarcomas of mammals. Characteristics shared by the oyster tumor and mammalian reticulosarcoma are: (1) relatively large blastoid (anaplastic?) cells with scant cytoplasm and enlarged, pleomorphic nuclei; (2) occasional binucleate or multinucleate cells; (3) many mitoses (many more than found in comparable normal or injured tissue); (4) focal (tumor-like condition) rather than diffuse distribution of blastoid cells; and (5) altered patterns of reticulum fibers.Further histological and cytological study of this tumor, utilizing Lillie’s stain for reticulum and the mercury bromophenol blue method of Mazia, Brewer and Alfert for total protein, reveals that alterations in the connective tissue stroma result from invasion and replacement of normal vesicular connective tissue cells by large blastoid cells. These stromatic alterations are of two forms: (1) collapse and aggregation of remnants of normal reticulum fibers upon replacement or degeneration of normal vesicular cells; and (2) apparent (though, perhaps, not real) increase in reticulum in limited areas of the tumor as compared to normal areas in other oysters. The blastoid cells have a marked affinity for the total protein stain in cytoplasm and nuclei and show a much more intense staining for protein than do normal hemocytes, vesicular cells, and epithelial cells.Additionally, abundant mitotic activity suggests that active protein synthesis is a biochemical characteristic of oyster blastoid cells and supports the hypothesis that these are largely undifferentiated or anaplastic, neoplastic cells. It is recognized that active protein biosynthesis is a characteristic of normal cells undergoing division or elaborating secretory substances. However, the intensely proteinaceous nature of these cells is related to their neoplastic character since this oyster tumor and its unusual blastoid cells are highly abnormal and rare (1/5,000 oysters examined). The Alcian blue method for acid mucopolysaccharides showed no increase in acid mucopolysaccharides in the tumorous mantle epithelium, or in the lesion proper. No recognizable parasites or infectious agents were found in the oyster sections studied.The origin of the blastoid cell remains enigmatic. Additional specimens with this rare conditions are essential for further study. |
