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Vetdle Archive

Archive Case #152: Feline Injection Site Sarcoma

Cat veterinary case - Medium - August 2, 2026

Clinical Clues

  1. A cat is presented for a firm mass over the lateral thorax that has enlarged steadily over several weeks.
  2. The owner remembers vaccination in the region months earlier.
  3. The lump is fixed and extends deep into surrounding tissues.
  4. Fine needle aspiration is poorly diagnostic, but the mass behaves aggressively.
  5. These tumours are locally invasive and often require wide surgical planning.
  6. Injection site sarcoma is an important malignant soft tissue tumour syndrome in cats.

Diagnosis

Feline Injection Site Sarcoma

This case is most consistent with Feline Injection Site Sarcoma because the cat has a deep progressive mass at a prior injection region with aggressive local behaviour. The most important clues are the location and invasive nature, which make a simple post-vaccinal swelling less likely.

Learning review

Review the case evidence

Use the paired clues to explain how the evidence in this cat case supports the provided diagnosis, Feline Injection Site Sarcoma, then compare your reasoning with the case explanation.

Evidence checkpoints

Clues 1-2

  1. Clue 1: A cat is presented for a firm mass over the lateral thorax that has enlarged steadily over several weeks.
  2. Clue 2: The owner remembers vaccination in the region months earlier.

Clues 3-4

  1. Clue 3: The lump is fixed and extends deep into surrounding tissues.
  2. Clue 4: Fine needle aspiration is poorly diagnostic, but the mass behaves aggressively.

Clues 5-6

  1. Clue 5: These tumours are locally invasive and often require wide surgical planning.
  2. Clue 6: Injection site sarcoma is an important malignant soft tissue tumour syndrome in cats.

Self-review prompts

  1. After clues 1-2, what evidence from this cat case shaped your initial interpretation?
  2. When you compare clues 3-4 with clues 1-2, what changed in your reasoning about Feline Injection Site Sarcoma?
  3. How do clues 5-6 align with the case explanation for Feline Injection Site Sarcoma?

Educational Use

Vetdle archive cases are educational veterinary games for diagnostic reasoning practice. They do not provide veterinary advice, diagnosis, treatment, or professional medical guidance.