Exam 7 L. 9

Question 1

Mast cell tumors

Answer 1

1) 20% of canine cutaneous tumors
2) older dogs, mean age 8-9 years old
3) all considered malignant with unpredictable behavior
4) clinical signs are related to mast cell degranulation
- most are not sick (but, there may be paraneoplastic disorders such as gastric ulceration due to histamine causing increased HCl release)

Question 2

Canine mast cell tumors

Answer 2

1) unpredictable behavior
2) all malignant
3) regional lymph node involvement common
4) histologic grade, mitotic index, clinical staging and surgical margins are the most important predictors of survival

Note: the more aggressive the fewer the granules!

Question 3

Cutaneous MCT WHO clinical staging

Answer 3

1) stage 0:1 tumor, incomplete excision from dermis, without RLN involvement
2) stage 1: tumor confined to dermis, without RLN involvement
3) stage 2: 1 tumor confined to dermis, with RLN involve
4) stage III: multiple dermal tumors, large, infiltrating, with or without RLN involvement
5) stage 4: any tumor with distant metastasis

* Regional LN aspiration cytology most important test for clinical staging*

Question 4

Prognostic factors

Answer 4

1) mitotic index is an indirect measure of cell proliferation
2) counted as #mitotic figures per 10 high-powered fields
3) MI 5, median survival time 5 months

Question 5

Therapy for mast cell tumors

Answer 5

1) 1st goal of therapy is local disease control, typically with surgery and/or radiation therapy
2) the 2nd consideration is treating or preventing systemic spread with chemotherapy

Surgery and radiation therapy are the most successful treatment options

Question 6

KIT receptor: mast cells

Answer 6

1) KIT receptor is responsible for differentiation and proliferation of normal mast cells (some dogs have a defect in the KIT receptor)
2) associated with uncontrolled proliferation in 1/3 high grade mast cell tumors
3) do PCR to test for defective receptor tyrosine kinase
4) give Palladia (toceranib) to these dogs

Question 7

Paraneoplastic disorders related to mast cell degranulation

Answer 7

1) histamine release: G.I. ulcers, increased G.I. motility, peri-tumor inflammation, increased vascular permeability, hypotension, cardiac arrhythmia, bronchospasm
2) heparin release: local coagulation abnormalities during surgery
3) proteolytic enzymes, histamine, and vasoactive amines: delayed wound healing at site of removal!

Question 8

Systemic effects under anesthesia

Answer 8

1) massive systemic release of histamine
- life-threatening arrhythmias and hypotensive shock
- caused by hyperthermia, cryosurgery, or aggressive manipulation of large masses
2) for systemic effects of mast cell tumors related to degranulation during surgery:
- H1 blocker: diphenhydramine
- H2 blocker: ramotidine,famotidine

Question 9

Feline mast cell tumors

Answer 9

1) 2nd most common skin tumor!
2) cutaneous MCT: excellent prognosis, often minimal growth over months
3) chemotherapy indicated for non-resectable tumors, miliary form (100 superficial tumors)