Dermatopathology 2 - Neoplastic Skin Diseases

Question 1

Classification of skin tumours.

Answer 1

Epithelial:
- basal cell, squamous cell, sebaceous, apocrine, circumanal, anal sac.
Spindle cell:
- fibroblast, adipocyte, endothelial.
Round cell:
- lymphocyte, plasma cell, macrophage, mast cell.
Melanocytic:
- tumours metastatic to skin.

Question 2

1. Where do epithelial tumours arise from?
2. In what spp. are papilloma tumours most common?
3. In what other spp. can papilloma tumours arise?
4. Age of animals affected?
5. Papilloma cause?
6. Lesion presentation?

Answer 2

1. Epidermis.
2. Cattle and horses.
3. Dog, sheep, goat, cat, pig.
4. young.
5. Papillomavirus.
6. Solitary or multiple. Have a typical wart-like appearance. Severe in some cases. May regress spontaneously due to cytotoxic immune response. On haired skin, or in oral cavity. Cauliflower-like. Hyperplastic/keratotic squamous epithelium masses w/ fibrovascular stalk.

Question 3

1. Papilloma tumours are usually exophytic. What does this mean?
2. Sometimes get endophytic papilloma. What does this mean?

Answer 3

1. They grow out of the skin.
2. The tumours grow inwards - referred to as an ‘inverted papilloma’.

Question 4

1. Spp. affected by squamous cell carcinomas?
2. Associated with?
3. What areas most likely to be affected?
4. Nature of unusual form seen in large breed black-coated dogs?

Answer 4

1. Any/all.
2. UV - starts as dermatitis as a result of UV exposure. .
3. Thin haired, unpigmented skin of eyelids or ear tips, genitalia in horses.
4. Aggressive - can invade the bone as well as the skin.

Question 5

Squamous cell carcinomas histopathologically.

Answer 5

Invasive cords of squamous epithelium.
Cell shapes variable w/ prominent intercellular bridges.
Some will produce aggregates of pink keratin = ‘keratin pearls’.
Pleomorphic (able to assume different forms).
Mitotic figures can be numerous - compatible w/ aggressive tumour.
Scirrhous = fibrous tissue forms around the mass.
Tumours on the digits in cats can rarely be associated w/ metastasis from pulmonary carcinomas. Skin tumour may be apparent before signs of the pulmonary mass develop.

Question 6

Tumour of the hair follicles.

Answer 6

Arise from different levels of the hair follicle.
Most often solitary, benign, slow growing masses in older animals.
- can be multiple sometimes.
E.g. Infundibular cyst, infundibular keratinising acanthoma, trichoblastoma.

Question 7

Infundibular cyst.

Answer 7

Marked thickening of epithelial lining of hair follicle which pushes other structures in the skin upwards.
Keratin material forms within the cyst.
Cyst can occasionally rupture, releasing material onto skin surface.
Most commonly seen in dogs.

Question 8

Infundibular - keratinising acanthoma (dogs).

Answer 8

Material protrudes out of the infundibulum (opening of hair follicle).
Quite florid and complex in appearance.
Keratin material can have a toothpaste-like appearance clinically.
Benign.
May be multiple.

Question 9

Sebaceous gland masses.

Answer 9

Sebaceous hyperplasia.
Sebaceous adenoma.
Sebaceous adenocarcinoma - rare, infiltrative, may metastasise.
Old dogs - “sebaceous cysts”.

Question 10

Sebaceous hyperplasia histopathologically.

Answer 10

Benign proliferation of normal sebaceous glands.
Lots of glandular structures.
Sebaceous glands proliferate to an enormous number.
Gland structure otherwise normal.
Example of benign hyperplasia.

Question 11

Sebaceous adenoma.

Answer 11

Benign, may recur.
e.g. Meibomian adenoma on eyelids.
- sebaceous gland tissue less regular than tissues in hyperplasia..

Question 12

Circumanal / hepatoid gland hyperplasia / adenoma.

Answer 12

Sits around the perineum and down towards the prepuce in male dogs.
Called hepatoid glands as appearance under microscope similar to liver tissue.
May see one or more lesions.
Most common in older dogs.
May be castration responsive in some cases.
Can grow large - removal can be challenging, esp. if close to the anus.

Question 13

Anal sac apocrine gland tumours.

Answer 13

Old dogs.
Adenomas and adenocarcinomas (more common) can also arise from these cells.
- can be infiltrative and metastatic.
Can be associated with pseudo-hyperthyroidism and paraneoplastic hypercalcaemia.

Question 14

Spindle cell tumours.

Answer 14

From mesenchymal tissue in the dermis:
- fat.
- fibrous tissue.
- muscle.
- blood vessels.
- bone.
- cartilage.

Question 15

Lipoma.

Answer 15

Older dog.
Common.
One or multiple.
Anywhere on the patient.
Normal fat - adipocytes have appearance of normal fat cells on histopathology.
Benign but can grow to a large size.

Question 16

Liposarcoma.

Answer 16

Rare.
More aggressive.
See forms that infiltrate the muscle beneath the skin.
Cells do not look like normal adipocytes.

Question 17

1. Fibroma.
2. Fibrosarcoma.

Answer 17

1. Mostly cats.
   Well circumscribed.
   Bundles and whorls of collagen.
   Uniform fibroblasts.
   Benign.
2. More cellular.
   Pleomorphic (may form giant cells).
   More mitotic figures.
   Rapid growth.
   Infiltrative - challenging Sx removal.
   Non- metastatic.
   In dogs as well as cats.
   - a form in young cats may be viral associated (rare).
   More commonly associated with injection sites: - vaccine associated feline fibrosarcoma.
   – challenging to manage.

Question 18

1. Most common skin tumour in the horse?
2. Cause?
3. Areas of body affected?
4. Multiple or single?
5. Histopathology?
6. Management?

Answer 18

1. Sarcoid.
2. Bovine papillomavirus (strongly associated).
3. Legs, trunk, face (or anywhere).
4. Often multiple.
5. Hyperplastic epidermis, whorls and bundles of collagen/fibroblasts, usually low mitoses.
6. May spontaneously regress.
   Locally infiltrative.
   Not metastatic.
   May recur after removal.
   Can be problematic due to location.

Question 19

Round cell tumours examples.

Answer 19

Histiocytic, lymphoid, mast cells, plasma cells (cells that infiltrate the skin).

Question 20

Histiocytoma…
1. Spp?
2. Age?
3. Growth rate?
4. Appearance, presentation and nature?
5. Histopathology?

Answer 20

1. Dogs.
2. Young (2-4yrs).
3. Rapid.
4. Solitary, raised, ‘strawberry button’, benign, spontaneous regression, no recurrence after excision.
5. Sheet macrophage-like cells.
   Dendritic Langerhans cells (dense blue infiltration of neoplastic round cells).
   Highly mitotic.
   Lymphoid infiltrate at base (as immune response develops and regression begins).

Question 21

1. Mast cell tumours in the dog.
   - histopathology.
2. Mast cell tumours in the cat.

Answer 21

1. Infiltrative.
   Local recurrence.
   Other sites.
   Metastasise to local LN.
   More malignant if scrotal, inguinal, preputial.
   Paraneoplastic effects (histamine release).
   Solitary or multiple.
   Anywhere.
   - Sheets of mast cells of varying differentiation.
   - Some may be granular as anticipated, and others not.
   - Eosinophils – cells w/ bright pink granules.
   - Lymphocytes – darker, smaller round cells.
   - Can grade for prognosis - either graded I-III (Patnaik), or graded high vs low (Kiupel).
2. Relatively benign.
   Rarely recur or metastasise.

Question 22

Melanocytoma…
1. Spp - breed types?
2. Presentation and nature?

Answer 22

1. Dog - pigmented breeds.
2. Solitary nodule of haired skin.
   Usually pigmented.
   Dermal infiltrate and epidermal nests - ‘junctional activity’.
   Melanophages - macrophages that have phagocytosed and released melanin pigment.
   Benign, potential to become malignant (rare).

Question 23

Malignant melanoma…
1. Spp.
2. Areas of body affected.
3. Px?
4. Histopathology?

Answer 23

1. Dog.
2. Digital, scrotal.
3. Not always poor, may metastasise to local LNs, lungs etc.
4. Hard to distinguish from benign, but generally:
   - more pleomorphic.
   - more mitoses.
   - more invasiveness.
   - diffuse epidermal infiltration higher than junctional.
   - not more pigmented – may be amelanotic.

Question 24

Equine melanoma.
- colour, age.
- presentation, areas of body.
- nature.

Answer 24

Grey horses, >6yrs old.
Multiple lesions - melanomatosis.
Perineum, ventral tail, genital, periocular, pinnal.
Pigmented.
Slow-growing - can become malignant.
Clusters melanocytes and melanophages.
Dermal.
Little junctional activity.