Feline injection-site sarcoma — Maine Coon mix, 7y.

Patient (synthetic)

Species

Felis catus

Breed

Maine Coon mix

Age

7 years

Sex

MN (neutered)

Weight

5.4 kg

Mass

Interscapular, 4cm × 3cm, fixed

The mass was first noticed by the owner approximately 3 months after a routine FVRCP vaccination at the interscapular site — classic 3-2-1-rule presentation (>3 months, >2cm, growing).

Diagnosis

Incisional biopsy returned a Grade II soft-tissue sarcoma consistent with feline injection-site sarcoma (FISS). Pre-operative CT showed local invasion into subcutaneous muscle without rib involvement; no pulmonary nodules.

Standard care recommendation: wide-margin excision (5cm lateral × 2 fascial planes deep) by a board-certified surgeon, with consideration of pre-op radiation given the location.

SciRouter Vet pipeline (synthetic run)

We ran the synthetic tumor through the comparative-oncology workflow that produced our canine case studies. Three things worth flagging up front:

• FLA training data is limited. MHCflurry's feline heads (FLAI-E, FLAI-H, FLAI-K) are transfer-learned from human + canine data with substantially smaller training sets than their DLA or HLA counterparts. Predicted IC50 values for feline targets are best read as ordinal ranks, not absolute affinities.
• Self-similarity filtering is harder for cats. The Felis_catus_9.0 reference proteome is well-annotated but with fewer published immunopeptidomics anchors than the canine reference.
• No vaccine cassette is proposed here. Cassette design (P5-6) requires sufficient confidence in the neoantigen ranking to justify ordering custom mRNA constructs. Feline-anchored case cassettes are not in current scope; this case stops at the comparative- oncology summary.

Cross-species comparative summary

Where FISS sits in the SciRouter Vet comparative-oncology atlas:

• Canine analog: none direct — FISS biology is feline-unique. The closest analog in dogs is high-grade post-vaccine soft-tissue sarcoma, which has been reported but is rare and not consistently tied to vaccination.
• Human analog: adult high-grade soft-tissue sarcoma — histologic similarity, treatment paradigm (wide-margin surgery + adjuvant radiation) is concordant.
• Translational angle: understanding inflammation-to-sarcoma transitions at injection sites in cats has implications for human implant-associated sarcomas (a rare but well-documented entity at breast implant and other prosthetic sites).

What we're not claiming

In the spirit of editorial neutrality and the disclosure posture we apply across SciRouter Vet:

• We are not claiming that the synthetic neoantigen rankings would be clinically actionable. FLA training data limitations make ordinal ranking the only honest framing.
• We are not proposing a vaccine cassette for this case. Cassette design requires higher confidence than the current feline pipeline supports.
• We are not implying this constitutes clinical decision support. The pipeline here is comparative-oncology framing only.
• We are showing that the SciRouter Vet pipeline runs end-to-end on a feline-anchored case, and we are documenting the training-data limitations honestly so future case studies (real feline cases from partner institutions) inherit the disclosure pattern.