PET/CT case suggests added value in grading canine leiomyosarcoma

A newly published case report in Frontiers in Veterinary Science suggests 18F-FDG PET/CT may help veterinary oncologists spot aggressive behavior in canine soft tissue tumors that biopsy alone can miss. The report centers on an 18-year-old intact male Alaskan Malamute with subcutaneous leiomyosarcoma whose tumor showed high FDG uptake on PET/CT, despite an initial biopsy that underestimated its aggressiveness. After surgery, final histopathology upgraded the lesion to a grade 3 poorly differentiated mesenchymal neoplasm with incomplete margins, and immunohistochemistry confirmed the diagnosis. (frontiersin.org)

That finding matters because leiomyosarcoma is an uncommon subtype within the broader canine soft tissue sarcoma group, and preoperative grading remains an imperfect tool. A commonly cited study on canine soft tissue sarcomas found only 59% concordance between pre-treatment and excisional biopsy grades, with nearly one-third of cases underestimated before surgery. More recent work has continued to examine ways to improve preoperative grading accuracy, including multiple biopsies and imaging-based approaches. (pubmed.ncbi.nlm.nih.gov)

In this case, the PET/CT signal aligned more closely with the tumor’s eventual behavior than the original biopsy did. According to the report, surgical resection took place about two weeks after PET/CT. Final pathology showed a high-grade lesion with incomplete margins, and the patient later developed local recurrence plus pulmonary lesions suspected to be metastatic within three months. The dog died six months after surgery after the pet parent declined recommended adjuvant chemotherapy in favor of palliative care. The authors describe the case as the first report of 18F-FDG PET/CT findings in canine subcutaneous leiomyosarcoma. (frontiersin.org)

The broader veterinary imaging literature provides some context for why this is plausible. Reviews of PET/CT in veterinary oncology describe the modality as a way to combine metabolic and anatomic information, with reported utility in detection, staging, treatment planning, therapeutic monitoring, and prognostication across several tumor types. PET/CT may detect biologic changes before structural changes are obvious, and it can help define active tumor burden more precisely than anatomy-based imaging alone. At the same time, published evidence in veterinary patients remains limited, and performance varies by tumor type. (pmc.ncbi.nlm.nih.gov)

Guideline-level recommendations still place tissue diagnosis at the center of decision-making. The 2026 AAHA Oncology Guidelines say prognosis and treatment planning often require diagnosis plus tumor grade, stage, or both, and note that biopsy and histopathology remain the standard route to definitive diagnosis. For soft tissue sarcomas, CT or MRI is already part of surgical or radiation planning in selected cases, especially when local extent matters. This new case does not change that standard, but it does suggest PET/CT could have value when conventional workups leave uncertainty about biologic behavior. (aaha.org)

Industry or expert reaction specific to this paper was limited at the time of writing, but the surrounding literature points in the same direction: veterinary oncology is pushing toward more precise preoperative assessment of sarcomas, especially where grade influences margins, staging intensity, and adjuvant recommendations. A recent consensus report on canine cutaneous and subcutaneous soft tissue sarcomas also underscores how prognosis is shaped by grade and surgical margins, while Cornell’s client-facing overview similarly emphasizes referral, imaging, and excision planning for challenging cases. (frontiersin.org)

Why it matters: For veterinary professionals, this is less about replacing biopsy and more about identifying when biopsy may not be telling the whole story. If a mass looks biologically “hot” on PET/CT but histology suggests a lower-grade process, that mismatch could affect how aggressively a team stages the patient, plans margins, discusses referral, or frames prognosis with a pet parent. It may be especially relevant in tumors where sampling error is a concern, or where incomplete first-pass surgery would meaningfully narrow future options. Still, this is a single case report, so the practical takeaway is caution, not adoption: PET/CT is promising as a precision adjunct, but not yet a standard for canine sarcoma workups. (frontiersin.org)

What to watch: The next step is whether larger studies can correlate FDG uptake with final grade, recurrence risk, metastasis, or survival across canine soft tissue sarcoma subtypes, and whether that added information changes management enough to justify cost and access barriers in routine practice. (pmc.ncbi.nlm.nih.gov)