• Dog (1,110:100,000 per year)
• 40% malignant
• Cats are fewer but most are malignant (70-80%)

1. Sharp surgery
2. Cryotherapy
3. Radiation therapy
• External beam
• Radioisotope
• Radioactive implants
4. Chemotherapy
5. Immunotherapy

1. Tumor initiating- DNA altering genome
2. One or more promotional events that develop the mass
3. Mutations (usually p53)- affects cell division
4. Apoptosis signaling
5. Failure in immune surveillance mechanisms

1. Breed predisposition
2. Infectious causes
3. Environmental factors
4. Chronic inflammation or infection
5. Behavioral factors

1. Age
2. Heredity/Breed
3. Sex/Reproductive status

• Most frequent in latter 1/3 of life
• Accumulations of mutations over time, diminishe immune system, lag time between initial transformation & clinical detection

• Females (esp. older, intact) have a higher incidence of tumors than males due to high incidence of mammary tumors
• Intact male dogs have a higher incidence of perianal gland tumors (related to testosterone stimulation)

• An abnormal growth that exceeds & is uncoordinated with that of normal tissue (serves no useful function) & persists without stimulation
• Cells free of normal growth control mechanisms and persists after cessation of the evoking stimulus

• Any type of localized swelling

• Synonymous with malignant neoplasia

• Study of neoplasia (oncos= tumor)

• Induction of neoplasia

1. Epithelial origin (oma vs. carcinoma)
2. Mesenchymal origin (oma vs. sarcoma)
• Spindle
• Round

1. Encapsulated or circumscribed
2. Grow by expansion
3. Slow rate of growth
4. No metastases
5. Well differentiated
6. Low mitotic index
7. Nuclear uniformity
8. nucleoli normal
9. Normal chromatin content
10. Cells polarized
11. Necrosis uncommon
12. Hemorrhage uncommon

1. Non-encapsulated
2. Grow by expansion and invasion
3. Rapid rate of growth
4. Metastases frequent
5. Undifferentiated or anaplastic
6. Increased mitotic index
7. Nuclear pleomorphism
8. Nucleoli prominent
9. Increased nuclear/cytoplasmic ratio
10. Cellular disorientation
11. Necrosis common
12. Hemorrhage uncommon

1. Invasion
2. Metastases
3. Anaplasia

1. Number of cells within the proliferating pool
2. Rate of cell death (highly variable)

• *** REMEMBER: high mitotic rate alone is not indicative of malignancy.  It onlyo determines the degree of proliferative activity of neoplastic cells! ***

• Metastasis

1. Expansion
2. Local invasion/infiltration
3. Metastasis

• Usually a benign form of growth
• Slowly compressive (so it can compensate)
• Can be life threatening if it occurs in a confined space (i.e. brain tumors)

• Malignant tumors posses the ability to invade & destroy the surrounding normal tissue
• Not well circumscribed
• Typical of sarcomas
• Can be life-threatening if large & not easily resectable

• Spread of neoplastic cells from a primary site to other body organs or tissues
• 3 methods:
1. Dissemination via lymphatic vessels
2. Dissemination via blood vessels
3. Implantation or seeding- esp. serosal surface (least common)

• Lymphatic spread
• Metastasis usually develops first in regional lymph nodes (follows natural lymphatic drainage route from primary site)

• When local regional lymph nodes are bypassed & metastases occur further away

• Hematogenous spread
• Most neoplastic emboli stop in the first downstream capillary bed
• Organ tropism also plays a factor in metastatic sites

• Factors that enhance the ability of metastases to grow that may be absent in filtering fields
• Ex: oxygen tension, basement membrane type, extracellular matrix, bound ligands or receptors, or local chemokine concentrations

How can neoplasis metastasize through implantation?

• Involves individualization of cells that arise within or penetrate a body cavity
• Separate from primary neoplasia --> float within body cavity (requires fluid) --> attach at a distant site with in the cavity --> neoplastic cells proliferate

1. Anatomic factors
2. Selectivity
• Adhesion molecules/cell surface feceptors

1. Fertile Soil Theory
• Suitable soil (favored sites) is due to the prescence of specific growth factors or lack of growth inhibiting factors in the target organs
2. Mechanical Theory
• Grows wherever it lodges
• Mechanical factors & chance influence success

1. Growth rate
2. Invasiveness
3. Metastatic capability
4. Hormonal responsiveness
5. Resistance to chemotherapeutic agents

• Tumor cells are genetically unstable & multiple mutations accumulate, resulting in a more malignant subpopulation