An Unusual Case of Collision Testicular Tumor in a Female DSD Dog

SIMPLE SUMMARY: Collision tumors (CT) consist of two independent neoplasm populations. Disorders of sexual development (DSDs) are characterized by various abnormalities of the genital tract. A phenotypically female 8-year-old Jack Russell terrier was submitted for clinical evaluation due to anomalous vaginal discharge and non-pruritic cutaneous bilateral symmetrical alopecia on the flanks. A voluminous mass was detected in the left quadrant area of the abdominal region and confirmed by ultrasound and necropsy examination. In the abdominal cavity, the left gonad was increased in size while the right one was decreased, as was the uterus. Histologically, the left gonad revealed a double neoplastic component (sustentacular tumor and interstitial cell tumor), whereas the right gonad showed coarctated seminiferous tubules. PCR amplification of the SRY and AMELX genes revealed the absence of a Y chromosome. To the best of our knowledge, this is the first report describing a case of a coexisting testicular collision tumor in a dog with testicular SRY-negative DSD. ABSTRACT: Collision tumors (CT) consist of two independent neoplasms with distinct neoplastic populations. Disorders of sexual development (DSDs) are characterized by atypical sexual development leading to various abnormalities of the genital tract. Sex reversal (SR) syndromes are a type of DSD characterized by a discrepancy between chromosomal sex and gonadal development (testes/ovaries) and the presence or the absence of the SRY gene. A phenotypically female 8-year-old Jack Russell terrier dog was referred due to anomalous vaginal discharge and non-pruritic cutaneous bilateral symmetrical alopecia on the flanks. During abdominal palpation, a voluminous mass was detected in the left quadrant area, later confirmed by ultrasound. The owner decided to proceed with euthanasia and necropsy. In the abdominal cavity, the left gonad was increased in size, the right one and the uterus were decreased, and the vagina and vulva appeared to be thickened. Histologically, both gonads were revealed to be testes: the left one was affected by a double neoplastic component (sustentacular tumor and interstitial cell tumor), whereas the right gonad showed coarctated seminiferous tubules. PCR amplification of the genes SRY and AMELX revealed the absence of the MSY region of the Y chromosome. To the authors’ knowledge, this is the first report describing a case of a testicular collision tumor in a DSD SRY-negative dog.