The First Case Report of a Primary Mast Cell Tumor Originating from the Inguinal Lymph Node in a Nine-Year-Old Female Maltese Dog

A splenic mass, ureterolithiasis, left third mammary gland tumor (MGT), and left inguinal lymph node enlargement were incidentally found during a routine examination of a nine-year-old intact female Maltese dog in South Korea in July 2024. The patient under-went comprehensive surgery, including the placement of a left ureteral stent, ureterotomy for the removal of ureterolithiasis, splenectomy for the splenic mass, and a left-side mastectomy that involved the left inguinal lymph node and left third MGT and ovariohysterectomy. The splenic mass, mammary gland mass, and inguinal lymph node underwent histopathological examination, resulting in the diagnosis of nodular hyperplasia, grade 1 mammary complex carcinoma, and metastatic mast cell tumor (MCT), respectively. The origin of the MCT from the inguinal lymph node was especially uncertain. Through a blood smear test, mast cell leukemia was ruled out, and a computed tomography (CT) scan was performed to determine the MCT’s origin. After CT scanning by veterinary radiologists and a biopsy of all possible masses, it was concluded that the MCT primarily originated from lymph nodes, which is extremely rare in dogs. The patient underwent 16 weeks of chemotherapy with a combination of prednisolone and vinblastine considering C-kit PCR result of left inguinal lymph node result after the surgical removal of the MCT. The patient is recovering well as of February 2025, just 7 months after first diagnosis. This re-port is significant for two reasons: first, the rarity of MCTs originating from lymph nodes other than the skin and gastrointestinal organs; second, the correlation between MGT and MCT growth, which will be investigated in a literature review focusing on molecular mechanisms.