Positron emission tomography (PET) could be used to predict the response of metastatic renal cell carcinoma (mRCC) to tyrosine kinase inhibitor (TKI) therapy within a couple of weeks of a patient beginning treatment, research suggests.
Changes in volume-based metabolic parameters of 18F-fluorodeoxyglucose (FDG) before and after 14 days of treatment with sunitinib, sorafenib or pazopanib significantly correlated with progression-free and overall survival, say Jacob Farnebo (Karokinska University Hospital, Stockholm, Sweden) and co-authors.
Overall, 35 patients with at least one metabolically active metastatic lesion underwent 18F-FDG-PET before and again 14 days (n=32) and 28 days (n=30) after beginning TKIs. Eight patients did not fulfil the study criteria and, after excluding these individuals, median progression-free survival (PFS) and overall survival (OS) was 159 days and 652 days, respectively.
A metabolic response was defined as a 30% reduction in one of two total lesion glycolysis (TLG) measures or the maximal standardised uptake (SUVmax), while progression was defined as a 30% increase in these values or a new metabolically active lesion, the team explains in BMC Cancer.
In addition, a 30% reduction in peak standardised uptake normalised to lean body mass (SULpeak) was considered a partial metabolic response.
Analysis revealed that patients were more likely to be considered to be responding to TKI treatment after 14 days using TGL measures than using SUVmax. Indeed, metabolic responses using TGL measures or SULpeak were significantly associated with both PFS and OS.
By contrast, there was no correlation between SUVmax and either survival measure for PET 14 or 28 days after treatment.
“A possible explanation could be that SUVmax only reflects a single voxel subjected to a highly variable degree of noise, and is thus less reliable for detecting subtle metabolic changes”, Farnebo et al suggest.
They conclude their study demonstrates the importance of the TGL and SULpeak volumetric PET parameters for assessing the response to TKI therapy after only 2 weeks and “propose these parameters as surrogate indicators of PFS and OS for prospective validation in a larger cohort.”
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