Spontaneous Myxosarcoma in a Cottontail Rabbit (Sylvilagus floridanus): Observation of Tubular Structures in the Endoplasmic Reticulum of Tumor Cells

Abstract

Ultrastructural examination of a spontaneous myxosarcoma in a 6-year-old cottontail rabbit (Sylvilagus floridanus) disclosed geometrically packed tubules (250 Å diameter) in the endoplasmic reticulum of >10% of tumor cell sections. The tubules were indistinguishable from structures previously described in virus encephalitis of rabbits and in virus-induced neoplasms of other experimental animals. They were also similar in dimensions and location to structures described in the cells of patients with connective tissue diseases. Present observations and review of the literature suggest that the tubular structures appear in two general forms: a tightly packed geometric or “crystalline” form presently identified and a less compact “tubuloreticular” form. Although their significance in the endoplasmic reticulum remains obscure, these tubular structures appear to have a limited distribution in mammalian tissues and usually are found in neoplasia or conditions associated with virus infection.