Is Leiomyosarcoma PET-CT Avid?
Yes, leiomyosarcoma is typically PET-CT avid, showing elevated FDG uptake that correlates with tumor grade and Ki67 proliferation index, though PET-CT is not routinely recommended for initial staging of soft tissue sarcomas including leiomyosarcoma.
FDG Avidity of Leiomyosarcoma
Leiomyosarcomas demonstrate significant metabolic activity on PET-CT imaging:
Retroperitoneal leiomyosarcomas show markedly elevated SUVmax values that increase with tumor grade: G1 tumors average SUVmax 4.15, G2 tumors 6.47, and G3 tumors 10.13, demonstrating a clear correlation between metabolic activity and malignant potential 1
SUVmax values correlate moderately with Ki67 proliferation index, providing prognostic information about tumor aggressiveness 1
PET-CT can differentiate leiomyosarcoma from benign leiomyomas with sensitivity of 92.3% and specificity of 75.0% using SUVmax cutoffs, with an area under the ROC curve of 0.909 1
The heterogeneous FDG uptake pattern reflects the internal necrosis and varying cellularity typical of these tumors 1
Current Guideline Recommendations for Staging
Despite leiomyosarcoma being FDG-avid, PET-CT is not recommended as a routine staging investigation for soft tissue sarcomas:
The 2025 UK guidelines explicitly state that PET-CT is not yet proven as routine investigation in sarcoma, though it may be considered before radical surgery such as amputation for primary or recurrent disease 2
Standard staging for leiomyosarcoma requires chest CT plus abdomen/pelvis CT, as leiomyosarcomas have a propensity for visceral metastases beyond the typical lung-only pattern of most soft tissue sarcomas 2, 3
PET-CT may be useful for prognostication, grading, and assessing response to chemotherapy, but should not replace conventional CT staging 2
Clinical Context for Leiomyosarcoma with Urothelial History
In a patient with both leiomyosarcoma and history of urothelial carcinoma:
PET-CT cannot reliably distinguish between the two malignancies based on FDG uptake alone, as both tumor types are typically FDG-avid 2
**Bladder leiomyosarcomas are rare (accounting for <5% of bladder tumors) but highly aggressive**, with adverse outcomes in >60% of cases and lung metastases occurring in 62% of metastatic cases 4, 5, 6
The standard workup remains tissue diagnosis via biopsy with immunohistochemistry to differentiate leiomyosarcoma (positive for desmin and smooth muscle actin) from urothelial carcinoma 7
Metastatic Pattern Detection
When leiomyosarcoma metastasizes, PET-CT shows specific patterns:
Primary leiomyosarcomas demonstrate local invasion on PET-CT, with hematogenous and lymph node metastases being rare at initial presentation 1
Postoperative recurrence/metastasis shows local recurrence and hematogenous spread (particularly to lungs), but lymph node metastasis remains uncommon 1, 4
Lung metastases are the most common site (62% of metastatic cases), making chest CT mandatory rather than relying on PET-CT alone 4, 3
Common Pitfalls to Avoid
Do not use PET-CT as a substitute for dedicated chest CT, as small pulmonary nodules may be missed on PET-CT due to respiratory motion and limited spatial resolution 3
Do not rely on PET-CT alone for initial staging, as the 2025 UK guidelines and NCCN guidelines recommend MRI for primary tumor assessment and CT for metastatic workup 2, 3
Do not assume high FDG uptake confirms malignancy in the bladder, as inflammatory conditions and urothelial carcinoma can also show elevated uptake requiring tissue diagnosis 2
Do not skip abdomen/pelvis CT in favor of PET-CT alone, as leiomyosarcomas specifically require dedicated abdominal imaging due to their visceral metastatic pattern 2, 3