MSK Oncology/Osteosarcoma Flashcards
describe the signalment of animals affected by osteosarcoma
- most commonly older (small juvenile subset (<3years)
- more common in large breed (>40kg)(appendicular skeleton): st. bernard, great dane, irish setter, rotties, dobermans, greyhounds, german shepherds, golden retrievers
- less common in small dogs, but higher chance in the axial skeleton
describe the anatomic locations of osteosarcoma
- appendicular (75%):
-most commonly metaphysial
-most commonly away from the elbow, towards the knee: proximal humerus, distal radius (MOST COMMON SITE), distal femur, proximal tibia
-forelimb 2x more common than hindlimb - axial (25%)
-ribs, mandible/maxilla, spine, skull
-more common in small breed - extraskeletal: rare
-spleen
describe the biologic behavior of osteosarcoma
- malignant cell: osteoblast
- locally invasive:
-destruction of local bone: lytic
-production of new bone: proliferative - highly metastatic:
-hematogenous: primary metastatic site is lung
-85% are negative for mets at diagnosis
but 90% will develop metastases
-other metastatic sites: other bones (<10% at time of diagnosis), rarely lymph nodes, intra-abdominal organs, and subcutaneous tissue
describe history and clinical signs of osteosarcoma (4)
- acute to subactute onset of lameness of varying severity
-degree of pain/lameness is variable, does not seem to line up with radiographic signs
-may be responsive to pain medications - sensitive to palpation of area of the lesion
- firm, painful swelling may be detected
- wide variation between patients!!
describe initial and radiographic diagnosis of osteosarcoma
- ortho/neuro exam: to localize the pain
- 2-view radiographs of the area
-can be lytic or proliferative, usually both
-often metaphyseal
-radiographic signs: - Codman’s triangle:
- cortical lysis
- new bone proliferation
- ill-defined zone of transition
- almost never crosses the joint space!!
radiographic differential diagnoses to consider:
1. other primary bone tumor
2. metastatic neoplasia
3. bone cyst
4. osteomyelitis (especially fungal)
describe tissue diagnosis of osteosarcoma
- fine needle aspirate: sedate heavily! plus analgesia, clip and clean, sterile prep
-ultrasound guidance to an area of cortical lysis can increase yield- but will HURT
-FNA of nearby soft tissue swelling may be diagnostic
-alkaline phosphatase stain: differentiates OSA from other sarcomas
-up to 85% diagnostic
-cells will be primarily mesenchymal - biopsy:
-fluoroscopy guidance can increase yield
-options: open or needle core biopsies
describe staging of osteosarcoma
- minimum: thoracic evaluation (3-view chest rads)
- nuclear scintigraphy:
-Tc99 radiotracer taken up by active bone remodeling, MAY be consistent with primary bone tumor or metastasis
-can be difficult to interpret (especially DJD versus neoplasia) - full body CT scan to detect other lesions
what are the 2 categories of treatment of osteosarcoma?
- definitive intent: do either
-amputation OR
-limb-sparing surgery OR
-stereotactic radiation therapy
-plus carboplatin for best outcome - quality of life/palliative intent
-medical pain management
-bisphosphonate
-palliative radiation therapy
-if pathologic fracture: palliative amputation versus euthanasia
describe amputation as definitive treatment for osteosarcoma
- most common/standard of care
- myth: large to giant breed dogs do poorly after amputation; they DO! just have to pick right candidate (full ortho/neuro exam, most are already so painful they are already 3 legged lame)
- myth: forelimb amputees do worse than hindlimb amputees: just may take a little longer to adapt but do really well once figure it out
- best outcome: amputation + adjuvant chemotherapy (carboplatin)
- micrometastasis: cells have made their way through the lung most of the time by when you make diagnosis = not detectable but most will still develop osteosarcoma post-amputation
describe limb sparing surgery as definitive treatment for osteoarthritis (big picture be aware of)
- options limited by:
-lesion location (disal radius, ulna)
-surgeon availability (very few offer this) - ulna = ulnectomy
- radius: surgical removal of affected bone with a margin followed by reconstruction (hardware or allograft)
- pros:
-avoid amputation
-similar long term outcome as amputation - cons:
-radius: high post-op infection rate (from hardware)
-post-op hardware failure possible
-expensive and low availability
describe sterotactic radiation therapy as definitive treatment of osteosarcoma (big picture be aware of)
1, high dose highly targeted radiation
- 3 tx over 3 days
- pros:
-avoid amputation
-similar long term outcome as amputation - cons:
-post tx fracture rate can be high
-hella expensive
-multiple anesthetic episodes
describe adjuvant chemotherapy
- median survival time with surgery/local control alone is 4-6 months; if supplement with chemotherapy MST is 10-12 months, delays onset of metastasis
(KNOW THESE MONTHS NUMBERS!!!) - most common adjuvant is carboplatin
describe medical pain management
lots of options and can combine, but will eventually fail to control pain; the absolute minimum you should provide
- NSAIDs
- gabapentin
- tramadol, amantadine, tylenol codeine
describe palliative radiation therapy
- many protocols, but most common is 1 treatment a day for 2 consecutive days
- at last 75% respond: pain reduction within 2-3 weeks
- lasts 2-4 months and can be repeated if effective
describe bisphosphonates
- inhibit osteoclasts, leading to reduced bone destruction (a major source of pain)
- 30-50% response rate: improved pain management
- IV every 3-4 weeks until no longer effective
- may be synergistic with palliative radiation therapy
- nephrotoxic and decreases renal clearance, so check renal valus prior to EVERY dose!!
describe palliative amputation
in cases of pathologic fracture or uncontrolled pain
describe control and prognosis of axial skeleton osteosarcoma
- often more difficult to obtain adequate local control (can’t amputate spine or pelvis); may have to rely on radiation therapy (palliative or SRT)
- variable prognosis:
-mandible (+/- other flat bones of the skull): lower metastatic rate, improved prognosis with local control
-ribs: pretty poor
what factors favor a better OSA prognosis? what favor a worse prognosis?
better:
-mandible
-digit, metacarpal, metatarsal
worse:
-ribs or proximal humerus
-<3 years old
-elevated serum ALP (not always bc of tumor!)
-high grade
-peripheral monocyte county above 0.4 (even though this is within normal limits for most labs)
-presence of metastasis
what is the biggest difference for feline osteosarcoma?
metastatic rate is HELLA lower! great prognosis! tripod cats do really well!!
