Rat Mammary Neoplasia

What is the most common neoplasia in rats?

The most common neoplasia in rats is mammary neoplasia. Most commonly (>90%) these tumours are benign fibroadenomas. Which is great news!
However these fibroadenomas can grow very large, very quickly! And they can develop anywhere on the comprehensive mammary chain of rats. Potentially anywhere on the dorsum, or from ventral neck to inguinum. They can also develop in males and females!

What causes them?

Potential predisposing factors include:
  • Prolactin – A hormone that is associated with mammary tissue development and function – high levels of prolactin can lead to hypertrophy and benign neoplasia
  • High levels of progesterone, and low levels of oestrogen
  • Overfeeding your rat!

How can we treat and prevent them?

Surgery is recommended to remove the mass, under a general anaesthetic with appropriate heat, pain relief and aseptic technique. It is also worth considering a custom made e collar to prevent your rat from chewing at the site post-surgery!

It is worth removing masses (even if benign) if:
  • Becoming quite large (>10% patient weight)
  • Encroaching on normal anatomical structures/impeding motion
  • Becoming infected or traumatised

It is highly likely that rats with one mammary tumour, will develop more in the future. This is due to ongoing research into the predisposing factors leading to mammary tumours and the best methods for treatment.
In addition to surgical removal, it could be beneficial for your rat to discuss:

  • Neutering (ovariectomy/ovariohysterectomy) – as young neutered rats have lower circulating levels of prolactin (a hormone associated with rat mammary neoplasia).
  • Anti-prolactin therapy – Cabergoline – to reduce one of the hormonal factors leading to mammary tumour development.
  • Feed/calorie restriction – overfeeding can increase the size of the pituitary gland, leading to more prolactin development, and subsequent mammary neoplasia.

  • Vella, D. Time Online 2018 – Rabbits & Rodents. CVE.
  • Monks, D. Mammary Neoplasia in Rats. UPAV Conference. 2015.
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