Feline malignant mammary tumors. III. Presence of C‐particles and intracisternal A‐particles and their relationship with feline leukemia virus antigens and RD‐114 virus antigens

Thirty-six feline mammary tumors were examined by the electron microscope, and by the indirect immunofluorescence (IFA) test with anti-FeLV and anti-RD-114 serum. In 11 (30.6%) tumors intracisternal A-particles (IAP) were found. One of these tumors contained a few particles with an electron-dense nucleoid in the cisternae of the endoplasmic reticulum. In 7 (19.4%) other tumors C-particles were found and in the remaining 18 (50.0%) no particles at all could be detected. In 11 (30.6%) tumors FeLV antigens and in 20 (55.5%) tumors RD-114 virus antigens were present. In 9 (25%) tumors we found a high (greater than 1/64) and in 11 (30.6%) tumors a low (greater than 1/16 less than or equal to 1/64) titer. There was a good correlation between the presence of C-particles and the demonstration of FeLV-antigen but none between IAP and FeLV antigens. No correlation was found between RD-114 virus antigens and any type of particle. Morphologically, the IAP found in feline mammary tumors were indistinguishable from the IAP present in mammary tumors of some inbred mice strains. The IAP in feline mammary tumors possibly represent an endogenous virus, different from RD-114 virus. The role of these viruses in the etiology of feline mammary tumors is discussed.