Neoplasia

Question 1

Describe the aetiology of Mast Cell Tumours

Answer 1

It is a neoplasia affecting the histiocytes (mast cells). Certain breeds are predisposed e.g. beagle.
Differing grades of tumour from benign to highly malignant.
Approximately 20% of skin tumours in dogs are mast cell tumours

Question 2

Describe the pathophysiology of mast cell tumours

Answer 2

Mast cells usually play a role in the allergic immune response- the granules contain histamine.
When tumours develop, the mast cells undergo malignant transformation where they have uncoordinated mitotic division.
Degranulation of mast cells in the tumour can lead to systemic signs (the release of histamine causes other responses e.g. anaemia)

Behaviour of the mast cells malignant transformation depends on the grade.
They are often skin tumours
Occasionally they are found in the GI tract, spleen, bone marrow. Graded 1-3 according to how differentiated they are. Grade 3 has the poorest prognosis.

Question 3

What are the clinical signs of Mast cell tumours?

Answer 3

Very varied appearance!
Benign or low-grade may be small, slow-growing masses in the skin.
Higher grade masses cause more histamine release that may be associated with swelling, inflammation, ulceration.
Some can occur in the subcutaneous layer.
Rare, but if animals have a large number of mast cell tumours, they can cause GI ulceration, vomiting, melaena, perforated ulcer.

Question 4

How can mast cell tumours be diagnosed?

Answer 4

1. Biopsy
   - can be incisional where they only remove a slice or part of the mast cell tumour.
   - can be excisional where they remove the entire mast cell tumour ( and a surrounding area of 2-3cm of normal tissue).
   - assesses the grade of the tumour
   - external
   - GA/ sedation required
2. FNA - confirms the diagnosis
   - use a syringe to pick up cells, put on slide and send away.
   - easy to do, quick procedure, cheap
   - animal can remain conscious so can be done in consult in theory.
   - doesn’t always give us the cells we need
3. Evaluation of local lymph nodes to assist with grading - can take a FNA from them
4. Imaging - to detect any metastases.
   - if animal is under GA for a biopsy anyway, then can radiograph to check for spread at same time

Question 5

What is the aetiology of osteosarcoma?

Answer 5

It is a primary malignant neoplasm of the bone tissue (primary = it does not come from a secondary spread. it is a unique bone tumour)
Most commonly affects large breed dogs (e.g. great Dane)
Middle aged-older dogs
Rare, but can affect cats

Question 6

What is the pathophysiology of osteosarcoma?

Answer 6

Osteocytes undergo malignant transformation leading to the breakdown of bone tissue and abnormal deposition of bone.
Damage to the bone tissue may lead to the weakening of the bone and cause pathological fracture (a fracture caused by something that wouldn’t normally break a limb)
Is also commonly metastatic spread to the lungs.
Usually found in the metaphysis of long bones - commonly limb bones e.g. humerus. They don’t cross joints usually and they can technically occur anywhere e.g. spine)

Question 7

What are the clinical signs of osteosarcoma?

Answer 7

Lameness (limping) - caused by pain and deformity of the limb.
Swelling of the site - due to infiltration of neoplastic tissue. Very painful and reactive to this area.
Pathological fracture - due to weakening of the bone.
Coughing - due to metastatic spread to lungs.

Question 8

How is osteosarcoma diagnosed?

Answer 8

1. Radiography
   - can visualise the affected limb, evaluate the lung fields
   - cheaper than biopsy
   - signs may be suggestive of osteosarcoma
   - CT/MRI more sensitive to detecting metastases
2. Biopsy
   - definitive diagnosis
   - tells us the type of cancer