Final Exam - Tumors of the Skeletal System Flashcards
what is the most common primary bone tumor?
osteosarcoma
what is important about the biphasic distribution with osteosarcoma?
effects young dogs & older dogs
18-24 months & then older than 7 years
what dogs are typically affected by osteosarcoma?
large & giant breed dogs
what breeds have shown predisposition to developing osteosarcomas?
great danes, dobermans, rottweilers, scottish deer hounds, & greyhounds
T/F: dogs weighing > 40kg account for 30% of osteosarcoma with only 5% occurring in the axial skeleton
true - dogs under 15kg account for about 5% of cases with 59% occurring in the axial skeleton
compared to large/giant breed dogs, appendicular osteosarcomas in small dogs have what differences?
histological grade & mitotic index are significantly lower when compared to large breed dogs
median survival time following amputation alone without chemo is longer
what anatomical locations are osteosarcomas most common?
75% occur in the appendicular skeleton particularly in the metaphyseal region of long bones with front limbs more commonly affected than hind limbs
what saying can help you remember the predilection sites for osteosarcomas?
toward the knee & away from the elbow
where are the most common sites for osteosarcomas in the axial skeleton?
mandible 27%, maxilla 22%, spine, cranium
T/F: local & distant metastasis is less common for axial osteosarcoma when compared to appendicular osteosarcoma
true - 40 to 60% for axial vs > 90% for appendicular
when is local recurrence most common for axial osteosarcoma?
greatest for maxillary ~60%
what is the most common extraskeletal primary site for osteosarcoma? what are some other locations?
spleen
mammary tissue, subcutaneous tissue, gi tract, kidney
what are extraskeletal osteosarcomas characterized by?
formation of osteoid in absence of bone involvement
what is the median survival time for extraskeletal osteosarcoma?
wide or radical excision - 90 days
marginal excision - 13 days
why must histology of small biopsy samples of osteosarcomas be interpreted with caution?
histological pattern may vary within the tumor
what is the basis of histological diagnosis for osteosarcomas?
tumor osteoid
what is the pathology of osteosarcoma?
malignant mesenchymal tumor with cells producing an extracellular matrix of osteoid
what are the histological subclassifications based on for osteosarcomas?
type & amount of matrix & the characteristics of cells - but no significant difference in subtype & clinical outcome
what are some examples of histological subclassifications for osteosarcoma?
osteoblastic, chondroblastic, fibroblastic, giant cell, poorly differentiated
what factors are associated with pathological fractures from osteosarcomas?
femur is the most common location to fracture with humerus being 2nd
radius is least likely to fracture
lytic lesions more likely to fracture
how does osteosarcoma spread?
hematogenously
T/F: metastatic disease is very common for osteosarcoma
true - 85-90% will die from metastatic disease
where is the most common metastasis site for osteosarcoma?
lung
others include other bones, lymph nodes, subcutaneous tissue, eyes, liver, & adrenal glands
what should be included in your workup prior to determining most suitable treatment for osteosarcoma?
CBC/chem/UA, thoracic rads/ct scan, abdominal ultrasound, & bone scan
what is step one when working on an osteosarcoma patient?
triage the patient, address pain/discomfort before starting workup
what may be seen on radiographs that is supportive of an osteosarcoma?
cortical lysis causing a pathological fracture, soft tissue extension, sunburst/pallisading pattern, & codman’s triad (periosteum is elevated & new bone is laid down resulting in deposition of dense new bone on the cortex)
what is the sensitivity & specificity of doing an ultrasound guided FNA for diagnosing osteosarcoma?
97% sensitive & 100% specific
T/F: results for any tissue biopsy of a suspected osteosarcoma should be interpreted cautiously because until the whole tumor is evaluated with histopathology a final diagnosis can’t be made
true
what percentage of animals have lung mets at the time of presentation?
10%
why is a thoracic ct better than thoracic radiographs for osteosarcoma patients?
nodules are more likely to be detected on CT - use to highlight the concept of stage migration
why is an abdominal ultrasound recommended for dogs with suspected osteosarcoma?
risk of mets to the abdominal cavity is very low but it is usually done in older dogs to evaluate for the presence of a 2nd neoplastic disease
why is a bone scan recommended for dogs with suspected osteosarcoma?
secondary bone mets are present in about ~8% of dogs at the time of diagnosis, so any osteoblastic activity will be identified including osteoarthritis, infection, & neoplasia
very sensitive but not specific
what are 5 negative prognostic factors associated with osteosarcoma?
- age - younger dogs have a shorter survival time
- anatomic location - humerus, extraskeletal OSA has aggressive systemic behavior with a high met rate, & head OSA
- serum ALP - elevated levels pre-op & 40 days post-op develop earlier mets
- disease stage - stage III, measurable mets, pulmonary, bone, soft tissue, lymph nodes
- monocyte count - some cells counted with monocytes may be myeloid suppressor cells that suppress anti-tumor immune response
what are some local treatment options for osteosarcoma?
amputation, limb spare - surgical or radiation using stereotactic radiation therapy
what are some palliative treatment options for osteosarcoma?
oral analgesia, bisphosphonates, & palliative radiation
what is an example of systemic treatment for osteosarcoma?
chemotherapy
T/F: amputation without chemo for osteosarcoma is palliative
true - survival time is 3-4 months
T/F: prior orthopedic surgery makes an animal a poor candidate for an amputation for osteosarcoma
false
what is the criteria for surgical limb spare for osteosarcoma?
no evidence of mets, primary tumor affects <50% of the bone, absence of pathological fractures, less than 360 degrees of soft tissue involvement, firm definable soft tissue mass, & distal radius
what are the major complications associated with limb sparing?
recurrent local disease, infection, & implant failure
what is the prognosis for limb sparing?
80% experience good to excellent function
what is the typical chemo regimen for dogs with osteosarcoma?
carboplatin - total of 4 treatments every 3 weeks
cisplatin & doxorubicin
what is the approximate survival time for a dog treated for osteosarcoma with amputation & chemo?
12 months - 20% alive at 2 years
when treating metastatic disease, what does it depend on?
timing of metastasis, location/clinical signs, & what drugs have already been used
what drug has shown positive preliminary evidence for treating metastatic disease for osteosarcoma?
palladia - toceranib phosphate
what is the MOA of tramadol?
centrally acting opiate-like agonist that has primarily mu-receptor activity
dosing is 2-5mg/kg PO every 6-8 hours
what is the MOA of gabapentin? what are the disadvantages of using it?
unknown mechanism of action - takes 24 to 48 hours to reach therapeutic concentrations
sedation & ataxia are most common side effects
what is the MOA of amantadine?
unclear but antagonizes NMDA receptor dosing is 305 mg/kg every 24 hours
what side effects are associated with amantadine?
behavioral change (sedation) & acute gi upset
what is the MOA of pamidronate/zolidonate?
inhibit bone resorption without inhibiting the process of bone mineralization
induction of osteoclast apoptosis
what is the impact of pamidronate & chemo on survival times in dogs with appendicular osteosarcoma treated with palliative radiation therapy?
MST with RT & chemo - 307 days
MST with RT & pamidronate - 69 days
what is the most effect treatment for osteolytic bone pain in humans?
radiation therapy
what does radiation therapy do for osteosarcoma?
induction of cell death in malignant osteoblasts & resorbing osteoclasts, depletion of inflammatory cells, inhibition of osteoclast precursor recruitment, alleviation of bone pain, & no acute or late side effects
T/F: amputation should be considered as palliative therapy in dogs with asymptomatic metastatic disease
true
