Regression of subcutaneous lymphoma following removal of an ovarian granulosatheca cell tumor in a horse.

The study explores the case of an Arabian mare that showed regression of subcutaneous lymphoma post removal of an ovarian granulosa-theca cell tumor, hinting at a possible hormonal link to the ebbing and rising of these tumors, specifically related to progesterone serum levels.

Case Overview

• The research revolves around a 9-year-old Arabian mare that was admitted for evaluation due to multiple subcutaneous nodules and infertility.
• Fine-needle aspiration of one such nodule resulted in a cytologic diagnosis of histiolymphocytic lymphoma.
• A mass associated with the left ovary was detected via palpation per rectum and transrectal ultrasonography.
• Excision of the ovarian tumor was performed, which was histopathologically identified as a granulosa-theca cell tumor.
• It was observed that the removal of the ovarian tumor led to the regression of the subcutaneous nodules.

Hormonal Relationship Investigation

• The horse’s vet noted that the subcutaneous nodules had previously disappeared and then recurred after being administered with a synthetic progestin. This prompted further investigation into a possible hormonal link with the lymphoma.
• Immunophenotyping and estrogen and progesterone receptor assays were conducted for this purpose.
• The lymphoma was classified as a T-cell rich B-cell lymphoma. Moreover, the estrogen receptor assays turned out negative, but the progesterone receptor assays were positive.

Clinical Observations

• The clinical observations regarding the subcutaneous lymphoma in horses indicate that the cyclical nature of these tumors may be associated with factors such as the estrous cycle, pregnancy, foaling, and lactation.
• The presence of progesterone receptors implied a relationship between serum steroid hormone concentrations like estrogen and progesterone, and the subcutaneous lymphoma.