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A case in Oncology

KC Pattinson's Mast Cell Tumour

Written by Charlotte Johnston DVM MVetSc DipACVIM (Oncology) MRCVS American Specialist in Veterinary Oncology 

KC, an 8-year-old female Shar Pei was referred to SCVS for management of a mass over her left lateral tarsal region. A fine needle aspirate had been taken by her referring vet which confirmed the mass to be a mast cell tumour (Fig.1, Fig.2) .

Fig.1-2 Fine needle aspirate from mass over left lateral tarsal region. Note clustering of mast cells in a background of erythrocytes. Extracellular matrix, likely collagen, and stringy chromatin from broken nuclei are also present.

 

On presentation KC was bright, alert and vital parameters were within normal limits. A 35x35mm cutaneous mass was present on the lateral aspect of the left tarsus. The skin was thickened medial to the tarsus. The left popliteal lymph node was prominent but not enlarged. Further examination including rectal examination was unremarkable. 

After discussion with the owner, KC was admitted to the hospital for further investigations. Haematology and serum biochemistry profiles revealed a mild elevation in creatinine but there were no other clinically significant changes. Under general anaesthesia a CT scan of her thorax, abdomen and left hind limb was completed. The thoracic and abdominal CT scans were unremarkable. The scan of her left hind limb revealed a 10 x 5 mm irregular region of nodular thickening of the skin located on the caudal aspect of the distal tibia just proximal to the calcaneus. The left popliteal lymph node and left inguinal lymph node were prominent when compared to the right. Fine needle aspirates were taken from the liver, spleen, left popliteal lymph node and left inguinal lymph node. The liver and splenic aspirates showed no evidence of metastatic disease. However, evidence of metastatic disease was confirmed within the aspirates of the lymph nodes. 

 

Unfortunately, due to location and size of KC’s mast cell tumour it was not possible to remove the mass with wide margins as we would typically recommend for mast cell tumours. Given the evidence of metastatic disease it was advised to proceed with a marginal excision of the mass in addition to removal of the metastatic popliteal and superficial inguinal lymph nodes. Histopathology confirmed a grade II/ low grade mast cell tumour. 

KC recovered uneventfully from anaesthesia and surgery and returned to see the oncology department once her surgical incisions had healed. The most important factors taken into consideration when determining the recommended ongoing plan for KC were:

  • Histopathological grade
  • Completeness of surgical excision
  • Evidence of metastatic disease
  • Location of the primary tumour

Low to intermediate grade tumours (as in KC’s case) in general have a low incidence of metastasis. However, this was unfortunately not the case for KC. Due to the evidence of metastatic disease, despite surgical excision, adjuvant chemotherapy was recommended. KC was started on a 12-week protocol of vinblastine. This involves 8 intravenous treatments with vinblastine (initially weekly, then every other week) over a course of 12 weeks. Vinblastine is generally an extremely well tolerated chemotherapy drug and our goal for our patients is that they are leading a completely normal life at home during treatment. 

KC is now nearing the end of her chemotherapy protocol. She continues to have a fantastic quality of life and there is no evidence of recurrence or progression of her disease. Following completion of chemotherapy KC will undergo repeat staging to confirm her disease is in remission and she will return to oncology department every 3 months for ongoing monitoring.