Author's address (for correspondence): MB Koivisto, Department of Clinic, Surgery and Animal Reproduction, FMVA, UNESP – Univ Estadual Paulista, 16050-680 Araçatuba, Brazil. E-mail: firstname.lastname@example.org
This report addresses an atypical transmissible venereal tumour in an 8-year-old bitch that was pluriparous and seropositive for leishmaniasis. There were ascites and a serosanguineous discharge from the vulva, but no lesions on the external genital mucosa. An aspirate of the peritoneal fluid showed mononuclear round cells characteristic of transmissible venereal tumour (TVT). Exploratory laparotomy revealed light red, granulomatous structures in the peritoneum, omentum, spleen, liver and uterine horns. Cytological and histopathological tests confirmed the diagnosis of intra-abdominal TVT. Dissemination of the TVT to several organs inside the abdominal cavity probably resulted from immunosuppression caused by leishmaniasis, which favoured the presence and aggressiveness of TVT.
Transmissible venereal tumour (TVT) is a neoplasia naturally occurring in susceptible dogs due to the transplantation of viable neoplastic cells by means of sexual contact, causing a rupture of the major histocompatibility complex (MHC) barrier (Mukaratirwa and Gruys 2003). The tumour generally first affects the genital mucosa, but extragenital tumours (skin, anal, oral and ocular mucosa) have been observed and associated with social behaviour (licking, fights etc.; Eze et al. 2007).
Canine leishmaniasis is caused by a flagellate protozoan of the genus Leishmania, which parasitizes macrophages of vertebrate hosts (Marino et al. 2012). The host response may lead parasitized macrophages to disseminate to the spleen, liver and bone marrow, causing chronic infection and reducing the immune response (Silva 2007). The presence of the parasite inside or around neoplastic cells suggest that the tumour has a histiocytic origin (Albanese et al. 2002).
There are reports of concomitant TVT and leishmaniasis (Albanese et al. 2006; Marino et al. 2012), including atypical and more aggressive cases of the tumour. Our aim is to describe clinical and pathological findings of a case of disseminated TVT in the abdominal cavity associated with leishmaniasis.
An 8-year-old bitch, of undefined breed, and with a suspected pyometra, was presented to the Araçatuba Veterinary College Hospital. Clinical history included four unremarkable pregnancies and regular oestrous cycles; with the last oestrus occurring 2 months before with copulation by an unknown male. The owner reported the use of contraceptives during the previous 2 years and could not recall the active pharmaceutical ingredient. Further complications included abdominal distension with ascites, emesis, appetite loss, dyspnoea and congestion of the oral and ocular mucosa. Gynaecological examination revealed no external lesions on the vulva, a hyperaemic vaginal mucosa and sparse serosanguineous fluid. Digital examination of the vagina revealed no perceptible nodular structures. Vaginal cytology showed few red blood cells, neutrophils, parabasal cells suggestive of diestrus, however, inconclusive for TVT. Ancillary tests included a complete blood count, serum biochemistry, radiography, ultrasonography and routine serological diagnostic tests for leishmaniasis (ELISA).
The serum biochemistry and blood count results were within normal limits, although there was hypoalbuminemia (15.7 g/l; reference values: 26–33 g/l). Radiography showed a generalized increase in the abdominal radiopacity and reduced definitions between organs, which indicated the presence of fluid within the abdominal cavity. Ultrasonography revealed increased echogenicity in the mesenteric region, suggestive of peritonitis; a complex echogenic structure of irregular borders dorsal to the urinary bladder, but neither uterine horn could be visualized. In addition to neutrophils (17%), lymphocytes (5%), eosinophils (4%) and rare mastocytes, aspiration cytology of peritoneal fluid had a predominance of mononuclear round cells (75%) with a low cytoplasm:nucleus ratio and basophilic-vacuolated cytoplasm, which was suggestive of TVT.
Exploratory laparotomy revealed serosanguineous fluid in the abdominal cavity. The peritoneum, omentum, spleen, liver, uterine horns and broad ligament had their serosal surface covered by small, light red granulomatous structures (Fig. 1). A mass of approximately 7.0 cm × 5.0 cm × 5.0 cm could be visualized close to the abdominal aorta and the urinary bladder and was adhered to the peritoneum. As the tumour was disseminated, total splenectomy, nodulectomy, ovariohysterectomy and partial omentum removal were performed. The animal recovered after surgery but had an unfavourable prognosis, dying 10 days after surgery.
The cytological characteristics of the mass located on the peritoneum was similar to that observed from the aspiration cytology of the peritoneal fluid, revealing ovoid and round cells with centralized nucleus and intensely vacuolized and basophilic cytoplasm, characteristic of a TVT. Mitotic figures were present and some mononuclear infiltrate and neutrophils were found among tumour cells. Histopathological examination of the uterine horns showed TVT cells on the serous and endometrial surface, in addition to cystic endometrial hyperplasia. The histopathological aspect of the tumour, both in the uterus and in the omentum, indicated a relatively uniform loss of layers and cords of ovoid cells. The cells had generally indistinct borders, large round nucleus with one single centralized nucleolus and moderate, light pink cytoplasm. Based on the mitotic activity and the small number of lymphocytes, the TVT was classified as highly invasive and in progressive growth phase. Cytological and histological diagnoses were consistent with TVT associated with leishmaniasis, subsequently confirmed by ELISA.
In the present case, the absence of external genital lesions made it difficult to explain the primary foci of the neoplasia. However, presence of neoplastic cells in the uterine horns and the history of mating with a stray dog indicate that TVT was possibly sexually transmitted and subsequently disseminated to the omentum, peritoneum, spleen and liver. Other dissemination routes would include the haematogeneous (Albanese et al. 2006) or the lymphatic route (Marino et al. 2012). As the animal was positive for leishmaniasis, immunosuppression could have favoured the neoplasia dissemination. Leishmaniasis reduces the host immune response, benefiting the implantation, invasion and dissemination of TVT cells to other sites, which may result in the persistence of lesions (Marino et al. 2012). Immunosuppression increases the metastasis rate and TVT malignancy, preventing the tumour regression (Cohen 1973).
In this case, the neoplastic cells in the peritoneal fluid, suggestive of TVT, were influential for a clinical suspicion of TVT. To our knowledge, there are no reports of leishmaniasis associated with TVT including description of metastases to the uterus, omentum, peritoneum, spleen and liver, as well as the presence of neoplastic cells in the peritoneal fluid. Most cases involve cutaneous dissemination of the neoplasia as multiple nodules (Albanese et al. 2002) sometimes covering the genital region (Catone et al. 2003). Presence of the parasite in genital smears of positive dogs with TVT has been detected in only 25% cases (Marino et al. 2012); in the present case, however, no amastigote form, free or inside the neoplastic cells, was found.
In this report, we documented an uncommon presentation of TVT associated with presence of neoplastic cells in the peritoneal fluid without any external genital lesions. Immunosuppression probably favoured the tumour invasion and aggressiveness. Clinicopathological findings did not indicate the metastatic route but can aid in the understanding of the biological behaviour of TVT associated with leishmaniasis for future cases.
Conflicts of interest
None of the authors have any conflicts of interest to declare.
Trevizan JT; Carreira JT; Souza NC; Carvalho IR; Lima VMF; Gomes PBC and Rozza DB were involved in diagnosis, clinical treatment and case description. Orlando CMB; Trevizan JT and Koivisto MB were involved in discussing the case and writing the manuscript.