Our facility obtained a three-and-half-year-old, female cynomolgus monkey (Macaca fascicularis) from a reputable breeding facility in the Philippines. We housed the animal in our Association for Assessment and Accreditation of Laboratory Animal Care (AAALAC) International-accredited facility for a one-year period. During this period, the cynomolgus monkey received a physical examination that did not reveal any abnormalities. We performed complete blood count, serum chemistry, intestinal parasite, rectal culture, and TB tests during this time; and the results of all tests were normal or negative.

We never used the monkey in an experimental study. The animal received a commercial monkey diet (Certified Primate Diet 5048, PMI Nutritional International, Inc., Brentwood, MO) along with fresh fruit daily. Water was available ad libitum. We housed the monkey in a room maintained at 72°F and 50% humidity with a 12:12-h light:dark cycle. Several months later we examined the monkey again during routine physical examinations of the colony in our animal facility. During the examination, we palpated a mass on the left side in the caudal region of the monkey's abdomen. The mass was round, firm, multilobulated, and approximately 3–4 cm in diameter. All other examination parameters and tests were within normal limits. We took an abdominal radiograph, which revealed a dense soft tissue mass in the left caudal quadrant of the abdomen. The mass did not displace any abdominal structures.

Based on the radiographic findings, we scheduled exploratory surgery so that we could remove the mass. The monkey received atropine (Henry Schein, Melville, NY) at 0.04 mg/kg i.m. and ketamine (Fort Dodge, Fort Dodge, IA) at 10 mg/kg i.m. We then anesthetized the nonhuman primate with isoflurane (BOC Group Inc., Madison, WI) and oxygen (JWS, Piscataway, NJ) at 1.5 and 2 L/min, respectively. We made a 10-cm abdominal incision just distal to the umbilicus to visualize and remove the mass. The mass was pink in color, with multifocal dark red areas and multifocal tan lobules of various sizes present on the surface. We removed the mass from the abdominal cavity, and it measured 4.5 × 3.0 × 2.0 cm. All other abdominal structures were normal on gross examination. The incision was closed routinely and the animal made an uneventful recovery. The cynomolgus monkey has remained clinically normal since the removal of the mass.

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