Abstract
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.
Highlights
We presented first evidence of diagnostic role of 68Ga-fibroblast activation protein inhibitor (FAPI)-positron emission tomography/computed tomography (PET/Computed Tomography (CT)) in head and neck cancer of unknown primary (HNCUP), and our study demonstrated that 68Ga-FAPI-PET/CT had the potential to improve the detection rate of primary tumor in HNCUP patients with negative FDG findings
Head and neck cancer of unknown primary (HNCUP) is defined as a metastatic disease in the cervical lymph nodes with an unidentifiable primary tumor [1], even after a thorough diagnostic workup according to the National Comprehensive Cancer Network [2] and American Society of Clinical Oncology guidelines [3]
Our results demonstrated that 68Ga-FAPI can dramatically improve the detection rate of primary tumor in HNCUP patients comparing to 18F-FDG
Summary
Head and neck cancer of unknown primary (HNCUP) is defined as a metastatic disease in the cervical lymph nodes with an unidentifiable primary tumor [1], even after a thorough diagnostic workup according to the National Comprehensive Cancer Network [2] and American Society of Clinical Oncology guidelines [3]. HNCUP constitutes 1-5% of all head and neck cancers [4,5]. The most frequent primary site of HNCUP is oropharynx, accounting for 80-90% [6]. Some factors, like small tumor volume, hidden location, slow growth rate, and tumor involution, hinder primary site identification [7]. The absence of primary tumor identification may result in uncertain treatment decisions and increasing psychological burden for patients with HNCUP [8]
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