Discussion: This is an excellent quality smear, containing high numbers of well-preserved, intact cells. Most of the cells are keratinized squamous epithelial cells (arrow), which are identified by their abundant, pale blue, glassy cytoplasm and angular cell borders. These cells retain their nuclei, but the nuclei are condensed and lack features of malignancy such as variations in nuclear size, prominent nucleoli, binucleation, or mitotic figures. Also present are high numbers of nondegenerate neutrophils (arrowheads). The background contains streaming nuclear debris (which should not be confused with bacteria) and a small amount of blood. No visible microorganisms are present. This is an example of squamous metaplasia of the prostate. Squamous metaplasia of the prostate in dogs usually results from excessive estrogen stimulation, which causes the prostatic epithelial cells to be replaced by non-neoplastic keratinized squamous epithelial cells. The cells may exfoliate and obstruct prostatic ducts, resulting in the formation of prostatic cysts or abscesses. Keratin is an inflammatory substance, and the neutrophils in this specimen are likely evidence of sterile inflammation; however, secondary or concurrent prostatitis cannot be ruled out. In this case, it is likely that the enlarged testicle contains a Sertoli cell tumor. Cryptorchidism is a known risk factor that predisposes dogs to Sertoli cell tumor development, and Sertoli cell tumors can produce high levels of estrogen. Other symptoms may include weight loss and feminization, including gynecomastia. While iatrogenic administration of exogenous estrogen may also cause prostatic squamous metaplasia, this usually causes atrophy of the testicles rather than enlargement. Squamous metaplasia is reversible, and typically resolves with removal of the estrogen source—usually, castration. Histopathologic evaluation of the enlarged testicle and bacterial culture and sensitivity to rule out prostatitis are recommended.
- Powe, J. R., Canfield, P. J. and Martin, P. A. (2004), Evaluation of the cytologic diagnosis of canine prostatic disorders. Veterinary Clinical Pathology, 33: 150–154. doi:10.1111/j.1939-165X.2004.tb00365.x
- Raskin R and Meyer DJ. Atlas of canine and feline cytology. Philadelphia, W.B. Saunders, 2001.