Evaluation of deslorelin implant on subsequent mammary tumors of rats (Rattus norvegicus)

Abstract Background : Mammary fibroadenomas are one of the most common tumors of female companion rats (Rattus norvegicus forma domestica). The objectives of this study were to determine if subcutaneous administration of a deslorelin implant following excision of fibroadenomas can prevent or delay development of additional mammary tumors and increase survival in companion rats. Methods : Female intact client-owned rats with benign mammary tumors were divided into three groups: no implant (n = 10), placebo implant (n = 10), or 4.7 mg deslorelin implant (n = 10) placed within two months of tumor excision. Rats were monitored for subsequent mammary tumors for ten months following treatment. Expression of estrogen α, progesterone, prolactin and androgen receptors stained by immunohistochemistry in primary masses of rats included in the deslorelin-treated group was evaluated using the Allred scoring system. Results : In the control non-implanted group, four of the ten rats developed another mammary tumor, including one anaplastic carcinoma. In the control placebo group, five of the ten rats developed another mammary tumor, including one ductal carcinoma. In the deslorelin-treated group, three out of ten rats developed another mammary tumor, including one adenocarcinoma. Median time between surgery and new mass detection did not differ significantly among groups (55 days in the deslorelin group vs. 77 days in the control placebo group, P = 0.25). Median survival times after surgery did not differ significantly among groups. No correlation was noted between receptor expression and response to treatment with deslorelin. Conclusions and clinical relevance : Deslorelin implants placed within two months of benign mammary tumor surgical excision were not associated with a decreased risk of developing subsequent mammary tumors, nor with an increased survival in female rats. Further studies are needed to define useful adjunct therapy to surgery.