Deslorelin implants in domestic rats

Most spontaneous mammary gland tumors in domestic rats are fibroadenomas. The treatment of choice is surgical removal but the appearance of subsequent masses is common due to the presence of persistent hormonal-promoting factors and the difficulty of performing complete excision.

Some studies in laboratory environments have shown that surgical spaying decreases the prevalence of spontaneous tumors when performed before they appear but prophylactical procedures are uncommon in these pets.

This prospective study was conducted in teaching hospitals and privately owned veterinary clinics. Rats presenting with a subcutaneous mass were recruited and only those with histologically-proven benign mammary tumors were included. The aim of the research was to find out whether the administration of deslorelin implants following the surgical removal of a tumor would prevent or delay the development of other masses and to evaluate the effectiveness of the implants on the survival of rats which had previously had benign tumors removed.

30 rats were included in the trial, 10 were implanted with deslorelin; 10 were implanted with a placebo and 10 (the control) were not implanted. The implants were placed between 21 and 50 days after tumor excision. The rats were monitored for 10 months following treatment.

The presence of hormone receptors, including estrogen and prolactin, was evaluated in the individuals in the deslorelin-implanted group using immunohistochemistry analysis – no correlation was found.
Some individuals developed a further mammary tumor (some with malignancy) following the excision of the benign mass: 4 were in the control non-implanted group, 5 in the placebo-implanted group and 3 in the deslorelin-implanted group. There was not a significant variation in the time between surgery and new mass detection or the median survival time between groups. Median survival times were also similar.

Based on this small study, we conclude that deslorelin implants are not likely to lessen the risk of developing further tumors following the excision of benign mammary masses and nor do they offer an increased survival rate. Nevertheless, investigations with larger samples are required to reach a firmer conclusion.

C. Vergneau-Grosset et al. Evaluation of deslorelin implant on subsequent mammary tumors of rats (Rattus norvegicus). Journal of Exotic Pet Medicine 31 (2019) 108-116.
https://doi.org/10.1053/j.jepm.2019.08.001