TY - JOUR T1 - The Added Value of <sup>68</sup>Ga-FAPI PET/CT in Patients with Head and Neck Cancer of Unknown Primary with <sup>18</sup>F-FDG–Negative Findings JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 875 LP - 881 DO - 10.2967/jnumed.121.262790 VL - 63 IS - 6 AU - Bingxin Gu AU - Xiaoping Xu AU - Ji Zhang AU - Xiaomin Ou AU - Zuguang Xia AU - Qing Guan AU - Silong Hu AU - Zhongyi Yang AU - Shaoli Song Y1 - 2022/06/01 UR - http://jnm.snmjournals.org/content/63/6/875.abstract N2 - 18F-FDG PET/CT plays an important role in locating the primary tumor for patients with head and neck cancer of unknown primary (HNCUP). Nevertheless, in some cases it can be challenging to locate the primary malignancy on 18F-FDG PET/CT scans. Because 68Ga-radiolabeled fibroblast activation protein inhibitor (FAPI) PET/CT has promising results in detecting different tumor entities, our study aimed to evaluate the performance of 68Ga-FAPI PET/CT for detecting the primary tumor in HNCUP patients with negative 18F-FDG findings. Methods: Eighteen patients (16 men and 2 women; median age, 55 y; age range, 24–72 y) with negative 18F-FDG findings were enrolled in this study. All patients underwent 18F-FDG and 68Ga-FAPI PET/CT within 1 wk. Biopsy and histopathologic examinations were performed in the sites with positive 68Ga-FAPI PET/CT findings. Results: 68Ga-FAPI PET/CT detected the primary tumor in 7 of 18 patients (38.89%). Among these 7 patients, primary tumor sites included the nasopharynx (n = 1), palatine tonsil (n = 2), submandibular gland (n = 2), and hypopharynx (n = 2). The primary tumors showed moderate to intensive uptake of 68Ga-FAPI (mean SUVmax, 8.79; range, 2.60–16.50) and excellent tumor–to–contralateral normal-tissue ratio (mean SUVmax ratio, 4.50; range, 2.17–8.21). In lesion-based analysis, 65 lymph nodes and 17 bone metastatic lesions were identified. The mean SUVmax of lymph node metastases was 9.05 ± 5.29 for 18F-FDG and 9.08 ± 4.69 for 68Ga-FAPI (P = 0.975); the mean SUVmax of bone metastases was 8.11 ± 3.00 for 18F-FDG and 6.96 ± 5.87 for 68Ga-FAPI (P = 0.478). The mean tumor-to-background ratios of lymph node and bone metastases were 10.65 ± 6.59 versus 12.80 ± 8.11 (P = 0.100) and 9.08 ± 3.35 versus 9.14 ± 8.40 (P = 0.976), respectively. Conclusion: We present the first evidence, to our knowledge, of a diagnostic role of 68Ga-FAPI PET/CT in HNCUP. Our study demonstrated that 68Ga-FAPI PET/CT has the potential to improve the detection rate of primary tumor in HNCUP patients with negative 18F-FDG findings. Moreover, 68Ga-FAPI had a performance in assessing metastases similar to that of 18F-FDG. ER -