Staging FDG-PET versus bone marrow aspirate/biopsy for assessment of metastatic bone involvement by rhabdomyosarcoma

Objectives To compare the performance of FDG-PET and bone marrow aspirate/biopsy (BMAsp/Bx) for detection of metastatic bone involvement (MBI) at initial staging of rhabdomyosarcoma (RMS).

Methods Included RMS patients underwent a staging FDG-PET/CT within 3 wks of BMAsp/Bx, and < 2 wks after start of chemotherapy. Whole body PET scans (accompanied by low-dose CT) were acquired ~1 hr after injection of ~12 mCi F18-FDG (scaled to BSA for patients <18 yrs) following a 6 hr fast. Skeletal sites on PET were visually graded on a 3-point scale (normal, equivocal and abnormal). Abnormal scans were categorized by number of lesions: limited (n < 10), widespread (n = >10). SUVmax values were recorded. Bilateral iliac crest BMAsp/Bx were performed per protocol. The standard of reference for MBI was clinical and imaging follow-up.

Results 88 patients (45F/43M) were eligible for the analysis. Histologic subtypes were: embryonal = 45, alveolar = 39, pleomorphic/spindle = 4. Median age at diagnosis was 13.3 yrs. PET scans were performed a median 0.1 weeks prior to BMAsp/Bx and 0.7 weeks prior to chemotherapy. PET was True Positive (TP) in 10/11 patients with positive BMAsp/Bx. BMAsp/Bx was positive in 10/17 patients with TP MBI on PET (4/10 limited MBI; 6/7 diffuse MBI). MBI was diagnosed by positive BMAsp (confirmed by RT-PCR demonstration of the presence of a PAX3-FKHR rearrangement), with negative BMBx, in 1 patient with discordant-negative PET scan. BMAsp/Bx was negative in 1 patient with equivocal PET, in whom MBI was proven by MRI. Average SUVmax for the hottest lesion per PET scan was 6.5 g/ml (range 2.4-11.7).

Conclusions FDG-PET performs better than bilateral BMAsp/Bx for detection of MBI at initial diagnosis of RMS. As it is non-invasive and does not require sedation or anesthesia, FDG-PET should be considered as a replacement for BMAsp/Bx in the initial staging and follow-up of patients with RMS.