Todayโs path rounds are on ๐๐ฎ๐ญ๐๐ง๐๐จ๐ฎ๐ฌ ๐ฅ๐ฒ๐ฆ๐ฉ๐ก๐จ๐ฆ๐!
๐๐ก๐๐ญ ๐ข๐ฌ ๐ข๐ญ?
๐๐ฎ๐ญ๐๐ง๐๐จ๐ฎ๐ฌ ๐ฅ๐ฒ๐ฆ๐ฉ๐ก๐จ๐ฆ๐ is a particular form of ๐ฅ๐ฒ๐ฆ๐ฉ๐ก๐จ๐ฆ๐ (tumour affecting the lymphocytes, a component of the immune system) that affects the skin. Typically, the animal presents with large masses or nodules throughout the affected area.
๐๐ก๐จ ๐ ๐๐ญ๐ฌ ๐ข๐ญ?
Any species can get this! Today we are going to talk about this disease in horses, though, because they have an interesting presentation compared to other animals.
๐๐ก๐ฒ ๐ข๐ฌ ๐๐ฎ๐ญ๐๐ง๐๐จ๐ฎ๐ฌ ๐ฅ๐ฒ๐ฆ๐ฉ๐ก๐จ๐ฆ๐ ๐ข๐ง ๐ก๐จ๐ซ๐ฌ๐๐ฌ ๐ข๐ง๐ญ๐๐ซ๐๐ฌ๐ญ๐ข๐ง๐ ?
Horses are particularly interesting because there have been a few reports of the masses disappearing during pregnancy in mares, and then coming back after the mare has foaled. Weird!
๐๐ก๐๐ญ ๐๐๐ฎ๐ฌ๐๐ฌ ๐ญ๐ก๐ ๐ซ๐๐ ๐ซ๐๐ฌ๐ฌ๐ข๐จ๐ง?
The scientific community hasnโt determined exactly whatโs going on in these cases, however they have shown that the tumour cells have ๐ฉ๐ซ๐จ๐ ๐๐ฌ๐ญ๐๐ซ๐จ๐ง๐ ๐ซ๐๐๐๐ฉ๐ญ๐จ๐ซ๐ฌ. Progesterone is the major pregnancy hormone, and is highest in pregnant animals. So when the mare becomes pregnant, the progesterone binds to the progesterone receptors in the tumour cells. Progesterone is known to have ๐๐ง๐ญ๐ข๐ฉ๐ซ๐จ๐ฅ๐ข๐๐๐ซ๐๐ญ๐ข๐ฏ๐ (prevent growth) effects on breast cancer cells in humans, by preventing the effects of their major growth hormone, estrogen. It seems that a similar effect is happening in these cutaneous lymphomas in mares!
๐๐จ ๐๐ฅ๐ฅ ๐๐ช๐ฎ๐ข๐ง๐ ๐๐ฎ๐ญ๐๐ง๐๐จ๐ฎ๐ฌ ๐ฅ๐ฒ๐ฆ๐ฉ๐ก๐จ๐ฆ๐๐ฌ ๐ซ๐๐ฌ๐ฉ๐จ๐ง๐ ๐ญ๐จ ๐ฉ๐ซ๐จ๐ ๐๐ฌ๐ญ๐๐ซ๐จ๐ง๐?
Unfortunately no, it seems that only about 50% of cutaneous lymphomas have progesterone receptors.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐๐ข๐๐ ๐ง๐จ๐ฌ๐๐?
Typically, the presentation of these masses will lead a veterinarian to doing a ๐๐ข๐จ๐ฉ๐ฌ๐ฒ (removal of a mass) or a ๐๐ข๐ง๐ ๐ง๐๐๐๐ฅ๐ ๐๐ฌ๐ฉ๐ข๐ซ๐๐ญ๐ (removing cells from a mass) to submit to a pathologist. The pathologist will look for characteristic large aggregates of lymphocytes in the sample provided, which would indicate a lymphoma. On a biopsy, the pathologist may also do ๐ข๐ฆ๐ฆ๐ฎ๐ง๐จ๐ก๐ข๐ฌ๐ญ๐จ๐๐ก๐๐ฆ๐ข๐ฌ๐ญ๐ซ๐ฒ, where a dyed antibody against a progesterone receptor is added to the tissue. This antibody will bind to progesterone receptors, if they are present, and allow the pathologist to see whether or not the tumour would be progesterone responsive. Cool!
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ญ๐ซ๐๐๐ญ๐๐?
If the tumour is progesterone responsive, horses may respond to injections of ๐ฉ๐ซ๐จ๐ ๐๐ฌ๐ญ๐ข๐ง, a progesterone analogue. However, these would have to be maintained for the entire remaining life of the horse, which is often not feasible. Otherwise, these horses may be treated with ๐๐ก๐๐ฆ๐จ๐ญ๐ก๐๐ซ๐๐ฉ๐ฒ, surgical removal, or simply left to live out their days as a very lumpy pony.
๐๐ก๐จ๐ญ๐จ๐ฌ
1-5) Examples of very lumpy ponies with cutaneous lymphoma.
6-7) What a pathologist might see on histology! Super pretty 
These slides are actually from a baboon but donโt tell anybody 
๐๐จ๐ฎ๐ซ๐๐๐ฌ
Taintor, J, Schleis, S. Equine Lymphoma. Equine Veterinary Education 2011;23(4):205-213.
Henson KL, Alleman AR, Kelley LC, Mahaffey EA. Immunohistochemical characterizationo of estrogen and progesterone receptors in lymphoma of horses. Veterinary Clinical Pathology 2000;29(2):40-46.
Photos 1-2 courtesy of Georgie Critchley.
Photos 3-4, 6-7 courtesy of Noahโs Arkive.
Photo 5 courtesy of Taintor et al.
