The early response of renal cell carcinoma to tyrosine kinase inhibitors evaluated by FDG PET/CT was not influenced by metastatic organ

BACKGROUND: Tyrosine kinase inhibitors (TKIs) have become the mainstay of treatment for advanced renal cell carcinoma (RCC), but it has been unclear whether the antitumor effect of TKIs depends on the organ where the RCC metastasis is located. We previously reported that the FDG accumulation assessed by FDG PET/CT, was a powerful index for evaluating the biological response to TKI. In this study we investigated the differences in FDG accumulation and the response to TKI as assessed by FDG PET/CT among various organs where RCC were located. METHODS: A total of 48 patients with advanced RCC treated with a TKI (25 with sunitinib and 23 with sorafenib) were evaluated by FDG PET/CT before and at 1 month after a TKI treatment initiation. The maximum standardized uptake value (SUVmax) of all RCC lesions were measured and analyzed. RESULTS: We evaluated 190 RCC lesions. The pretreatment SUVmax values (mean ± SD) were as follows: in the 49 lung metastases, 4.1 ± 3.3; in the 40 bone metastases, 5.4 ± 1.6; in the 37 lymph node metastases, 6.7 ± 2.7; in the 29 abdominal parenchymal organ metastases, 6.6 ± 2.7; in the 26 muscle or soft tissue metastases, 4.4 ± 2.6; and in the nine primary lesions, 8.9 ± 3.9. Significant differences in the SUVmax were revealed between metastases and primary lesions (p = 0.006) and between lung metastases and non-lung metastases (p < 0.001). The SUVmax change ratios at 1 month after TKI treatment started were -14.2 ± 48.4% in the lung metastases, -10.4 ± 23.3% in the bone metastases, -9.3 ± 47.4% in the lymph node metastases, -24.5 ± 41.7% in the abdominal parenchymal organ metastases, -10.6 ± 47.4% in the muscle or soft tissue metastases, and -24.2 ± 18.3% in the primary lesions. There was no significant difference among the organs (p = 0.531). CONCLUSIONS: The decrease ratio of FDG accumulation of RCC lesions evaluated by PET/CT at 1 month after TKI treatment initiation was not influenced by the organs where the RCC metastasis was located. This result suggests that TKIs can be used to treat patients with advanced RCC regardless of the metastatic site.