3′‐deoxy‐3′‐[18F]fluorothymidine positron emission tomography for response assessment in soft tissue sarcoma

Abstract

BACKGROUND: This study sought to determine whether [¹⁸F]fluorothymidine (FLT) positron emission tomography (PET)/computed tomography (CT) imaging allows assessment of tumor viability and proliferation in patients with soft tissue sarcomas who are treated with neoadjuvant therapy. METHODS: Twenty patients with biopsy‐proven, resectable, high‐grade soft tissue sarcoma underwent [¹⁸F]FLT PET/CT imaging before and after neoadjuvant therapy. Histologic subtypes included sarcomas not otherwise specified (n = 5), malignant peripheral nerve sheath tumors (n = 3), gastrointestinal stromal tumors (n = 3), leiomyosarcomas (n = 3), angiosarcomas (n = 2), and others (n = 4). Changes in [¹⁸F]FLT peak standardized uptake value (SUVpeak) were correlated with percent necrosis in excised tissue, whereas posttreatment [¹⁸F]FLT tumor uptake was correlated with thymidine kinase 1 (TK1) expression and Ki‐67 staining indices in excised tumor tissue. RESULTS: Tumor FLT SUVpeak averaged 7.1 ± 3.7 g/mL (range, 1.9‐16.1 g/mL) at baseline and decreased significantly to 2.7 ± 1.6 g/mL (range, 0.8‐6.0 g/mL) at follow‐up (P < .001); however, marked reductions in SUV were not specific for histopathological response. The posttreatment SUVpeak did not correlate with TK1 (P = .27) or Ki‐67 expression (P = .21). CONCLUSIONS: Marked reductions in [¹⁸F]FLT tumor uptake in response to neoadjuvant treatment were observed in most patients with sarcoma. However, these reductions were not specific for histopathologic response to neoadjuvant therapy. Furthermore, posttreatment [¹⁸F]FLT tumor uptake was unrelated to tumor proliferation by Ki‐67 and TK1 staining. These results question the value of [¹⁸F]FLT PET imaging for treatment response assessments in patients with soft tissue sarcoma. Cancer 2012;118: 3135–44. © 2011 American Cancer Society.