Comprehensive notes on soft tissue and bone tumors (lecture transcript)

Synovial cell sarcoma

  • Radiographic pattern differs from osteosarcoma; osteosarcoma will not cross over the cartilaginous surface or joint. In the example radiograph, there are multiple areas of lysis throughout the tarsal bone with the joint capsule originating on the distal tibia and proximal metatarsals. Malignant synovial sarcoma can infiltrate bone adjacent to the synovial tissue, hence joint/bone involvement.

  • Breed predispositions discussed; this variant is a bit more aggressive with a higher metastatic rate, so meticulous staging is advised.

  • Treatment note (as per lecture): amputation is the gold standard for local control. The transcript says “imputation” (likely a mis-say for amputation). Adjunctive chemotherapy may be required based on higher metastasis risk; grade and case-dependence apply.

  • Assessment/quiz context: current class average acceptable with many high performers; if concerns about content arise, reach out to the instructor.

Tumors of smooth muscle (Leiomyosarcoma and leiomyoma)

  • Origin: smooth muscle tissue; locations include GI tract, genital/urinary tract, and visceral organs.

  • Leiomyomas in the vagina/vaginal vault: described as well-circumscribed, noninfiltrative lesions that can grow from smooth muscle lining of the vagina.

  • Hormone relationship:

    • In intact female dogs, estrogen and progesterone can drive growth of vaginal smooth muscle tumors.

    • These tumors are often easy to recognize and treat when they are pedunculated.

  • Clinical management:

    • If the tumor is noninfiltrative and pedunculated, remove the bulk of gross disease and perform an ovarian hysterectomy to remove hormonal drive; this is usually curative.

    • If the mass is infiltrative and ulcerative with clinical signs (bleeding, etc.), it is unlikely to be a benign leiomyoma; more aggressive disease is possible. In sterilized (spayed) patients, hormone-driven growth is less likely.

  • Connecting note: a correlation with sex hormones in these tumors is discussed; some examples will be revisited in other lectures (osteosarcoma context mentioned).

Tumors of uncertain origin (MCSo/Sarcoma family)

  • MCSo sarcoma described as mesenchymal, lacking discrete anatomic origin.

  • Cell of origin: fibroblasts; produces a mixed matrix with mucinous components (cites a Shar-Pei-like material on skin as an analogy).

  • Behavior: behaves like other soft tissue sarcomas; not a special or distinct entity in behavior, but a diagnostic label you may encounter during removal of a soft tissue sarcoma.

  • Note: a case is planned for discussion in a future lecture hour.

Common features and general concepts for soft tissue sarcomas (STS)

  • Pattern recognition approach: many subtypes share overlapping characteristics; focus on consistent patterns to aid recall.

  • Typical presentation: pseudo-encapsulated, soft to firm, poorly defined margins; crab-like locally invasive growth but tends to stay localized if adequately addressed.

  • Metastasis:

    • Hematogenous spread is more common than lymphatic spread; low prevalence of lymph node metastasis overall, with the exception of synovial cell sarcoma which has a relatively higher metastasis rate.

  • Prognostic value of grade: grade strongly predicts likelihood of metastasis.

  • The 10-20-30 rule (grade-guided metastasis risk):

    • Grade 1 soft tissue sarcomas: metastasis risk
      Approx 10%

    • Grade 2 soft tissue sarcomas: metastasis risk Approx 20%

    • Grade 3 soft tissue sarcomas: metastasis risk Approx 30 to 50%

    • Implication: higher-grade variants may warrant adjunctive therapy even after complete excision.

  • Work-up and staging:

    • Fine-needle aspiration (FNA) is used first to name the tumor; diagnostic accuracy of FNA for sarcomas is around 50% (may be a bit higher in some studies).

    • If FNA is inconclusive, proceed to biopsy (incisional biopsy is typically used to obtain a tissue diagnosis and grade).

    • Thoracic staging (lungs) and regional imaging to assess resectability and metastatic risk.

    • Rationale: these tumors metastasize hematogenously rather than via lymphatics in most cases.

  • Biopsy and surgical planning:

    • Incisional biopsy is favored to obtain grade and histologic subtype while limiting seeding; the biopsy tract should be planned so it can be removed with the tumor later.

    • When a clear name/diagnosis is obtained, the next steps in treatment planning (includes dose of surgery and adjuvant therapy) are clarified.

  • Surgical goals and margins: wide excision is preferred with substantial margins to reduce local recurrence.

  • Nomenclature for margins:

    • Wide excision typically involves 3 cm of normal tissue circumferentially and at least 1 fascial plane deep (or two muscle planes if fascia is not present).

  • Radical options when needed:

    • Depending on tumor location, more aggressive, ablative surgeries may be considered, but these increase functional loss; margins and oncologic control take priority.

  • Recurrence and salvage:

    • Recurrence after wide excision is not common if margins are adequate; when margins are insufficient, recurrence can occur.

    • Marginal excision historically was associated with higher recurrence; however, recent data (2008 extremity study) show a substantial rate of local control even after marginal excision in extremity tumors.

  • Adjunctive therapy considerations:

    • Radiation therapy is used to sterilize microscopic disease at margins after incomplete excision or where margins are insufficient.

    • Scar revision or secondary surgical excision can yield acceptable local control with lower cost and faster recovery compared to radiation in some cases (recurrence in that study around 15%).

    • Metronomic chemotherapy has been explored as adjunctive therapy to reduce recurrence; some studies show longer time to recurrence with surgery + metronomic chemotherapy versus surgery + radiation.

    • Doxorubicin-based chemotherapy for high-grade sarcomas has shown little to no tangible overall benefit in a single study; decision to use chemotherapy should be case-based and consider risk vs. benefit.

  • Prognosis: overall prognosis is more determined by local control than distant metastasis in many cases; high-grade tumors have higher metastatic risk and poorer prognosis.

  • Practical surgical philosophy:

    • The goal is effective local control with permitted function where possible; wide margins are ideal but sometimes limb-sparing options with reconstruction may be pursued when feasible and safe.

    • If microscopic disease is found at margins, plan for adjuvant treatment (radiation, scar revision, or metronomic chemotherapy) as appropriate.

Feline injection-site sarcomas (FISS)

  • This is a distinct clinical entity with a strong association to adjuvanted vaccines (rabies and feline leukemia) given in the past; injection-type tumors can also arise from other injections, microchips, insulin, and other medications.

  • Pathogenesis concept:

    • Aluminum-containing adjuvants in killed vaccines likely drove an exaggerated immune/inflammatory response, promoting tumor formation at vaccination sites.

    • Historically observed after vaccines given in the interscapular region; often very large, infiltrative sarcomas that are hard to manage surgically.

  • Management principles:

    • Because FISS are highly aggressive, aim for aggressive local control with wide margins; tailor margins to anatomy and tumor behavior.

    • Tail-tip injections have emerged as a technique to minimize morbidity and improve access for complete tumor resections; the tail has less tissue and can be a more forgiving injection site.

  • Tail-tip vaccination strategy (evidence and rationale):

    • The University of Florida work suggests injecting vaccines into the tail tip produces an immune response with less tissue available for tumor development and allows easier access for surgical management if needed.

    • Practical approach: inject vaccines distal to the stifle and as far distally as possible; space out multiple injections to avoid excessive local antigen load.

  • 3-to-1 rule for vaccine site swelling:

    • If swelling persists >3 months, or if it exceeds 2 cm, or if it continues to grow after 1 month, then the swelling should be considered suspicious for FISS rather than a benign injection site reaction.

  • Diagnostic work-up and staging:

    • Cytology can help, but definitive characterization and histology are often needed to confirm FISS and exclude benign etiologies.

    • Because these tumors are aggressive, preoperative planning with cross-sectional imaging (CT) can map tendrils and guide margin planning (5 cm lateral margins and 2 tissue planes deep are suggested for some cases).

  • Surgical technique for FISS:

    • The recommended margins for feline FISS are typically 5 cm lateral margins and 2 tissue planes deep; such excisions may involve significant tissue loss and sometimes body wall reconstruction.

    • Even with aggressive margins, recurrence can be around 15%; without such margins, recurrence is much higher.

    • A complete, meticulous surgical plan is essential; CT-guided planning (CTS) can be helpful to visualize tendrils and plan dose of surgery.

  • Postoperative considerations and ethics:

    • FISS management is resource-intensive; owners should be counseled about potential need for extensive surgery and long recovery.

    • There is a veterinary pharmacovigilance and compensation aspect: pharmaceutical companies may offer assistance in cases where vaccine-related tumors are suspected, and these cases are reportable.

  • Practical takeaway: prevention by tail-tip injections and careful vaccine site planning, along with aggressive surgical management when tumors occur, can lead to long survival times despite aggressive biology.

Osteosarcoma (OSA) in dogs and cats

  • Epidemiology and species distribution:

    • Most common primary bone tumor in dogs and cats; in dogs, represents about 85% of bone tumors; dogs are disproportionately affected.

    • Large and giant breeds predominate; dogs >40 kg are at higher risk.

    • Male dogs are predisposed; neutering status appears to be a significant factor in risk.

    • There is a bimodal age distribution: young animals can get OSA (in addition to older animals).

  • Spay/neuter and breed risk data:

    • In Rottweilers, gonad demise is associated with a twofold increased risk of OSA.

    • Some studies suggest lifetime risk of OSA if gonad demise occurs early (before age 1) may approach 25% in some populations, underscoring breed-specific counseling needs.

  • Anatomy and site distribution:

    • Appendicular skeleton is most commonly affected; distal radius and proximal humerus are among the most common sites.

    • A mnemonic to remember sites: away from the elbow toward the knee, i.e., distal radius, proximal humerus, proximal tibia, distal femur.

    • In cats, axial skeleton involvement is more common than in dogs, but appendicular tumors still occur; cats have different distribution and biology.

  • Radiographic and pathobiology features:

    • OSA often begins in the medullary cavity and expands intramedullarily, breaking through the cortex and invading surrounding tissue; the classic “inside-out” pattern is a hallmark.

    • Periosteal reactions vary (from sunburst to Codman’s triangles) depending on lesion activity and bone response.

    • Different patterns of growth may occur: intramedullary, parosteal, or periosteal forms; parosteal and periosteal variants tend to be less aggressive than the conventional medullary/intramedullary form.

  • Diagnostics and staging:

    • FNA of bone lesions can be attempted, but definitive diagnosis often requires biopsy and histopathology due to overlapping appearances with other bone tumors.

    • Assessment of metastatic disease, particularly in the lungs, is critical since most dogs present with microscopic metastases at diagnosis.

    • Alkaline phosphatase (ALP) as a prognostic biomarker: elevated ALP is correlated with more aggressive disease and poorer prognosis; ALP is an inducible isoenzyme linked to bone turnover and tumor biology.

    • Lymph node assessment is not routinely predictive; routine lymph node sampling is not always necessary unless clinically indicated.

  • Prognosis and treatment philosophy:

    • 90% of dogs have microscopic lung metastases at diagnosis; systemic control is essential.

    • Local control is achieved primarily through limb-sparing approaches or amputation, depending on location and extent; the choice balances oncologic control with functional outcome and owner goals.

    • Traditional approach prioritizes aggressive local therapy (amputation or wide resection) due to propensity for local invasion and rapid progression if incompletely resected.

    • For better outcomes, capture of systemic disease and local disease control together is essential; two-phase strategy is standard: local control plus systemic management.

  • Practical clinical notes:

    • The most common sites are the four limbs (distal radius, proximal humerus, proximal tibia, distal femur).

    • The disease tends to metastasize early; lung evaluation and ongoing surveillance are critical.

    • In planning surgery, consideration of limb-sparing options vs amputation depends on tumor location, bone involvement, soft tissue coverage, and overall health of the patient.

  • Quick differential reminder for bone tumors (based on a typical exam prompt):

    • Osteosarcoma (osa) is the most common primary bone tumor in dogs; differentials include chondrosarcoma (cartilage origin), fibrosarcoma (fibrous tissue origin), and myxosarcoma (myxoid variants). Non-neoplastic mimics (fungal osteomyelitis) may occur regionally in fungal-endemic areas and should be considered in differential diagnoses.

  • Practical exam takeaways:

    • Always evaluate for metastatic disease early; plan local therapy with the expectation of microscopic metastasis.

    • When selecting treatment, consider activity level, prognosis, and owner goals; aggressive local control often yields long survival times, but distant disease can limit overall outcome.

Additional practical notes and clinical pearls

  • Biopsy and biopsy tract handling across sarcomas:

    • Always plan to remove the biopsy tract with the surgical margin if possible to reduce seeding risk.

    • Improper biopsy can seed tumor cells; proper technique and planning are essential.

  • Treatment sequencing and decision points:

    • If margins after initial surgery are inadequate, consider scar revision with more aggressive margin clearance before resorting to radiation.

    • Radiation can be effective for microscopic disease control but may not be ideal for every case; its cost, logistics, and recurrence rates should be weighed against scar revision or additional surgery.

    • Metronomic chemotherapy is an option for owners seeking non-traditional therapy; some studies show longer time to recurrence with surgery plus metronomic therapy vs surgery plus radiation, though evidence is variable.

  • Owner communication and expectations:

    • Discuss the likelihood of recurrence with incomplete margins and the potential need for adjuvant therapy.

    • For FISS and injection-site-related tumors, emphasize prevention strategies (tail-tip injections, vaccine site planning) and the potential for vaccine-related tumors to require aggressive, long-term management.

  • Practical surgical planning principles:

    • Consider anatomical boundaries and tissue planes; margins in perineal or extremity tumors may be limited by critical structures (e.g., anal sphincter, major nerves, vessels).

    • In select extremity tumors, limb-sparing approaches may be feasible with careful planning; otherwise, amputation is a salvage option.

  • Key numbers and protocols to memorize:

    • STS metastasis risk by grade: Grade 1 -> 10%, Grade 2 -> 20%, Grade 3 -> 30-50%

    • Surgical margins for STS: 3 cm radial margin, plus 1 fascial plane deep (or two muscle planes if no fascia is present)

    • FISS margins: typically 5 cm lateral margins and 2 tissue planes deep (tumor-specific considerations apply)

    • Injection-site sarcoma recurrence with adequate margins: about 15% in reported scar revisions; without adequate margins, recurrence risk is much higher

    • Osteosarcoma prognosis: high likelihood of microscopic lung metastasis at diagnosis; two-phase treatment approach (local control and systemic control) is standard

    • Tail-tip vaccination strategy: evidence supports easier management and potentially lower recurrence risk when vaccines are given at the tail tip; CT mapping (CTS) can guide surgical planning

Quick glossary of key terms

  • FNA: Fine-needle aspiration

  • CTS: CT-staging planning (computed tomography prior to surgery)

  • ALP: Alkaline phosphatase, a prognostic biomarker in osteosarcoma

  • Marginal excision: removal with minimal margins; higher risk of recurrence in many sarcomas

  • Metronomic chemotherapy: continuous low-dose chemotherapy with antiangiogenic effects

  • Adjuvant therapy: treatment given after the primary therapy to maximize effectiveness (e.g., radiation, chemotherapy)

  • Hematogenous metastasis: spread through the bloodstream

  • Periosteal vs intramedullary bone tumors: different growth patterns and aggressiveness

  • Injection-site sarcoma: vaccine-associated sarcoma, particularly in cats; high local aggressiveness requiring wide excision or more