Feline musculoskeletal tumours

Question 1

Outline feline cutaneous haemangiosarcomas

Answer 1

✜ Non-visceral haemangiosarcoma (cutaneous/ subcutaneous) is more common than visceral.
✜ Subcutaneous form is more aggressive than the cutaneous (dermal) form, with local recurrence
and metastasis widely reported.
✜ Common sites for the subcutaneous form are the flank, ventral abdomen, thorax and proximal pelvic limb.
✜ Adjunctive radiotherapy and chemotherapy with doxorubicin may be of value therapeutically, following surgical resection.

Question 2

Outline feline peripheral nerves sheath tumours

Answer 2

✜ Uncommon tumour affecting subcutaneous
tissues and muscle.
✜ Most often located around head, neck or limbs.
✜ Most are biologically benign. Malignant tumours
are not reported to metastasise; therefore, there is a good prognosis if completely excised. Local recurrence is likely with incomplete excision.

Question 3

Outline Feline restrictive orbital myofibroblastic

sarcoma (feline orbital pseudotumour)

Answer 3

Progressive debilitating disease of the orbit and
adjacent connective tissues, characterised by
restricted mobility of the globe and eyelids with
secondary corneal disease; insidious in onset.
✜ Unilateral or bilateral and may affect oral cavity
concurrently. No discrete mass.
✜ Computed tomography shows diffuse episcleral
thickening.
✜ Disease process involves infiltration of neoplastic
spindle cells, and collagen deposition within the
orbit, eyelids, periorbital skin and soft tissues.
Extension occurs along fascial planes to include
these sites.
✜ Prognosis is poor since aggressive treatment
is not yet reported. Cats are usually euthanised

Question 4

Outline feline sarcoids (cutaenous fibropapilloma)

Answer 4

✜ Reported in domestic cats in North America,
Europe, New Zealand and Australia, and in captive
African lions.
✜ Feline sarcoid-associated papillomavirus
(FeSarPV) DNA detected in lesions.
✜ Often located on head, lips, nares, footpads or
tip of tail.
✜ Non-encapsulated dermal masses consist of
spindle to stellate cells. Mitotic rate ≤1 per x 400
field. Overlying epithelium is hyperplastic with long
branching, rete ridges.
✜ Often contain mast cells amidst bundles of
collagen fibrils, which help to distinguish sarcoids
from schwannomas and fibrosarcomas.
✜ Metastasis not reported; therefore, prognosis is
good if completely excised. Local recurrence is
likely with incomplete excision

Question 5

How do you diagnose FISS?

Answer 5

Incisional biopsy

Question 6

What is the 3-2-1 rule?

Answer 6

recommends biopsy of a mass at an injection site:
✜ If the mass persists more than 3 months
✜ If the mass is greater than 2 cm in diameter
✜ If the mass is increasing in size 1 month after injection

Question 7

Compare canine and feline osteosarcomas

Answer 7

feline OSAs are slow growing compared with those in dogs, meaning that median survival times in cats (treated with amputation) are more than double those
of dogs (treated with amputation and adjunct chemotherapy): approximately 24–44 months versus 8–18 months, respectively
If mets occur it is usually late in the disease process
Cats more axial than appendicular (other way round for dogs)
Cats more FL Dogs more HL

Question 8

Why do cats seem to get lots of mets (e.g. pulmonary adenocarcinomas) to the digits?

Answer 8

possibly because of an increased blood

supply, which facilitates heat loss through their pads.

Question 9

How do you treat fibrosarcomas?

Answer 9

Surgical excision ‘en bloc’ removing 2 to 3 cm of normal tissue in all surgical plane
Note that these tumours have pseudocapsules of compressed neoplastic cells around them and should never be ‘shelled out’.

Question 10

Outline feline sarcoma virus

Answer 10

These lesions present as multiple fibrosarcomas in young cats. Such cases will invariably have been exposed to feline leukaemia virus (FeLV) as the feline sarcoma virus causing these lesions is a recombinant virus formed from the cat’s DNA and FeLV proviral DNA. Cats affected with feline sarcoma virus have a poor prognosis, but this condition is mercifully quite rare

Question 11

What may you see prior to a SCC presenting on the skin of a cat?

Answer 11

Pre-cancerous changes (actinickeratosis) can be seen preceding the development of the tumour.

Question 12

/Do SCC metastasis readily

Answer 12

SCCs have a low metastatic potential to lungs and local lymph nodes. Nevertheless, chest radiographs and FNA of drainage lymph nodes are recommended, especially prior to embarking on an extensive or lengthy course of therapy

Question 13

How can sx be used for SCC on the face?

Answer 13

Pinnectomy results in long survival times. Nasal planec-tomy is more cosmetically and functionally challenging, but also produces good survival times and is the treatment of choice for the larger, more invasive tumours.

Question 14

How can photodynamic therapy be used for SCC?

Answer 14

PDT involves the use of a chemical (photosensitiser),which is taken up preferentially by cancer cells. The chemical is activated by light of a certain wavelength, causing the death of cells that have absorbed the chemical. Since the therapy is selective for cancer cells and spares normal cells, the results can be very pleasing cosmetically. PDT has been used on feline SCCs and is best employed on very superficial lesions. It is currently associated with a high recurrence rate as the photosensitiseris applied as a cream and only penetrates the very top layers of the skin

Question 15

Outline the appearance of basal cell tumours

Answer 15

usually solitary and are mostly seen in older cats (the average age reported is 10 years). They can remain the same size for long periods of time. Basal cell tumours can have a variable appearance, sometimes looking solid, ulcerated or cystic. They are the most common pigmented tumour seen in cats and can have characteristics suggestive of aggressive behaviour both on cytology and histopathology

Question 16

How do you treat basal cell skin tumours

Answer 16

Surgery

Question 17

Outline mast cell tumours on the skin

Answer 17

commonly seen on the head and neck
Heparin and histamine granules within the mast cell can cause the lesion to appear erythematous after handling; in some cases, pruritus, ulceration and bleed-ing and/or gastrointestinal signs, such as vomiting and melaena, may be noted. Unlike dogs, MCTs in cats have poorly staining intracytoplasmic granules on histopathological or cytological examination. Mast cells are often seen associated with eosinophils in both eosinophilic granuloma complex and MCTs, and therefore an excisional biopsy rather than FNA is more useful to distinguish the two conditions

Question 18

What are the two types of MCT in cat

Answer 18

Atypical/ histiocytic MCTS are typically associated with young Siamese cats, but not invariably so. They are usu-ally multiple and regress spontaneously over a period of four to 24 months. The name arises from the fact that the neoplastic mast cells resemble histiocytes.

MASTOCYTIC MCTS are the more common cutaneous form of tumour and are seen in older cats. They are divided into ‘compact’ and ‘diffuse’ forms. Compact tumours have a low risk of metastasis and are not particularly infiltrative and and so can be surgically excised with a narrower margin than would be recommended for a canine MCT. Diffuse tumours have a higher incidence of metastasis and need a wider margin of excision.

Question 19

What is the relation of visceral and cutaneous MCTs

Answer 19

Visceral primary mast cell disease can lead to cutaneous metastatic disease, so deciding whether a splenic lesion is the primary or secondary disease can be difficult. All cats with diffuse or multiple MCTs should be staged by abdominal palpation, ultrasonography and routine haematology. If the spleen is involved, it is common to see a circulating eosinophilia and up to 40 per cent of cats have a buffy coat layer that is positive for mast cells.

Question 20

How may you treat metastatic MCT

Answer 20

Splenectomy has been reported to result in the spontaneous regression of metastatic lesions. Cats with metastatic disease do not fare as poorly as one would imagine, with median survival times of 12 to 19 months. Anecdotally, radiotherapy has been used successfully for incompletely resected non-metastatic cutaneous tumours. Chemotherapy has not been used with any measurable success. Prednisolone at 1 mg/kg daily has been used for multiple unresectable tumours, but this has little effect.

Question 21

Outline cutaneous lymphoma

Answer 21

Cutaneous lymphoma is relatively rare in cats. It is divided into epitheliotropic (sometimes referred to as ‘mycoses fungoides’) and non-epitheliotropic forms and can present as a solitary lesion or as a generalised skin disease. The latter form can be plaque-like, erythematous and pruritic, and may resemble any other dermatosis. Lymphadenopathy may be present, and can be associated either with infiltration of lymph node with disease or the inflammatory nature of the disease causing lymph node hyperplasia.

Question 22

How do you treat cutaneous lymphoma

Answer 22

Both types of cutaneous lymphoma can be relative-ly indolent and cats can live with the disease with little compromise to their quality of life. Solitary non-epitheliotropic lymphoma can be cured with surgery alone. However, it is not uncommon for other lesions to develop subsequently either as skin lesions or as more disseminated disease and so staging of the disease (including biopsy of the draining lymph node) prior to surgery, counselling the owner and regular monitoring afterwards is a sensible approach. A mixed bag of treatments has been used when surgery is not appropriate. Corticosteroids alone can ameliorate pruritus, but are not successful in inducing remission. Cyclophosphamide, vincristine and prednisolone have been used, as have chlorambucil and lomustine, but with short-term success

Question 23

How aggressive are visceral MCTs in cats?

Answer 23

Visceral MCTs are generally aggressive tumours and widespread metastasis is common. However, cats with primary splenic MCTs may achieve long survival but the prognosis is variable, and poor prognostic indicators include anorexia, weight loss and male gender.

Question 24

Compare the px for MCTs in cats with either multiple cutaneous masses v solitary masses

Answer 24

Multiple cutaneous MCTs may carry a more guarded prognosis than solitary tumours, but this may be controversial

Question 25

Where do feline MCTs metastasise to?

Answer 25

most common site of metastases is the local lymph node, which should be assessed by palpation/imaging and FNA; however, regional lymph nodes may also be affected. The most common sites of distant metastases are the spleen and liver, which should be assessed by (gentle) palpation, ultrasonography and FNA

Question 26

How far do you go with staging for MCTs in cats?

Answer 26

Minimum staging would involve evaluation of the local lymph node (palpation, ultrasound examination, FNA). Full clinical staging, based on lymph node aspirates, abdominal ultrasonography and FNA, plus thoracic radiographs and a buffy coat smear if indicated, should be carried out in cats presenting with:
Multiple masses

Palpable abdominal abnormalities

Clinical signs of systemic disease

Histologically poorly differentiated or anaplastic tumours

Visceral or cranial mediastinal tumours

Mastocytaemia (circulating mast cells).

Question 27

How can a MCT’s appearance help decide px?

Answer 27

MCTs are divided into well‐differentiated or poorly differentiated forms, which may be compact or diffuse, and any form may be pleomorphic. Poorly differentiated tumours and anaplastic tumours carry the worst prognosis but the majority of cutaneous mastocytic MCTs (50 to 90 per cent) are well differentiated and show benign behaviour.

Question 28

How may proliferation indices help inform px?

Answer 28

high MI has been associated with aggressive behaviour, as has a high amount of Ki‐67 protein, in a small number of cases. However, there are currently no validated ‘cut‐off’ values for MI or Ki‐67

Question 29

Compare surgical treatment of MCTs in cats and dogs

Answer 29

fewer cats with MCT are cured by surgery than dogs. The relatively small size of the patient means that it is frequently not possible to excise MCTs with wide margins, but this may be less critical for histologically well‐differentiated and/or compact tumours. However, postsurgical recurrence rates of up to 30 per cent are reported, irrespective of apparently complete excision. If a preoperative biopsy suggests the tumour has a more aggressive behaviour (a poorly differentiated or anaplastic tumour, high MI), a wide margin of excision should be used combined with adjunctive therapy as appropriate.

Question 30

How do you treat atypical MCTs in cats

Answer 30

Atypical (histiocytic) MCTs may undergo spontaneous regression, but if this does not occur marginal excision or periodical monitoring is warranted. There is no benefit in using corticosteroids in these cases.

Question 31

Outline receptor tyrosine kinases

Answer 31

Receptor tyrosine kinases (RTKs) are enzymes expressed on the cell surface that are switched on by the binding of a specific growth factor (ligand) paired with that receptor. These enzymes phosphorylate tyrosine residues, initiating a cascade of signals that cause upregulation of gene expression, and enhanced cell proliferation and survival. RTKs are often dysregulated in cancer, most often being switched on without the need for ligand binding.

Question 32

What are receptor tyrosine kinase inhibitors

Answer 32

Tyrosine kinase inhibitors (TKIs) act by blocking the activating phosphylation step. They have been developed to target specific RTKs known to be dysregulated in specific cancers, for example, KIT in mast cell tumours. Most TKIs also affect non‐target RTKs, and this can cause toxicity or additional beneficial effects. The RTKs involved in blood vessel formation (angiogenesis) in tumours also represent an important target for some TKIs.