Screening for distant metastases in patients with head and neck cancer: Is there a role for ¹⁸FDG-PET?

Summary

The detection of distant metastases and second primary tumours at the time of initial evaluation changes the prognosis and influences the selection of treatment modality in patients with HNSCC. Until recently chest CT was the single most effective test to screen for distant metastases in HNSCC patients. In this observational cohort study we prospectively compared the yield of whole body ¹⁸FDG-PET and chest CT to detect distant metastases and synchronous primary tumours. The results of whole body ¹⁸FDG-PET and chest CT were analysed in 34 consecutive HNSCC patients with previously established risk factors for the presence of distant metastases. Four patients were diagnosed with distant metastases or second primary tumours: CT as well as ¹⁸FDG-PET identified one patient with lung metastases and another with primary lung cancer. In addition, ¹⁸FDG-PET detected second primary tumours in two patients (hepatocellular carcinoma and abdominal adenocarcinoma). However increased uptake sites at ¹⁸FDG-PET in lung, liver and pelvis in five patients were not confirmed by other imaging modalities. The added value of whole body ¹⁸FDG-PET versus chest CT was to identify unknown malignancy in 6% of the patients. Confirmation of positive ¹⁸FDG-PET findings is feasible and necessary.

Introduction

The detection of distant metastases at the time of initial evaluation changes the prognosis and influences the selection of treatment modality in patients with head and neck squamous cell carcinoma (HNSCC). Distant metastases usually occur late in the course of the disease. The lungs, bone and liver are the most frequent sites of distant metastases. The prevalence of distant metastases in HNSCC at autopsy (37–57%) is much higher than in clinical studies (4–26%).1, 2, 3, 4 Distant metastases that appear during follow-up in patients who achieved locoregional control must have arisen from subclinical distant spread already present at the time of treatment. Patients with distant metastases are generally not considered curable and almost always receive only palliative treatment.⁵

Because of the relatively low incidence of distant metastases at presentation, only patients with risk factors should undergo evaluation for distant metastases. In a previous study⁶ in the 1990s, we evaluated the value of screening for distant metastases retrospectively in 101 patients with advanced stage HNSCC, scheduled for major surgery, who underwent chest radiographs, chest computer tomography (CT), ultrasound or CT scan of the liver and bone scintigraphy. We identified several risk factors for development of distant metastases and found that chest CT was the single most important technique that was available for screening for distant metastases in HNSCC patients at that time. Besides lung metastases, chest CT can also detect primary lung cancer, mediastinal lymph node metastases, bone metastases in spine and ribs, and can be extended to the liver. Therefore, we continued performing chest CT only in screening for distant metastases in HNSCC patients with risk factors: three or more cervical metastases, bilateral or low-jugular (level IV) cervical metastases, cervical metastases larger than 6 cm, recurrence or second primary tumours.

Despite negative screening and locoregional tumour control some patients develop distant metastases. These distant metastases must have been present at diagnostic work-up, but were apparently below the detection limit of screening tests. If distant spread occurs early after major surgery with curative intent these patients probably underwent inappropriate extensive treatment.

Thus a more sensitive diagnostic technique which preferably examines the whole body is needed. Positron emission tomography (PET) using the radiolabeled glucose analog 18-fluoro-2-deoxy-glucose (¹⁸FDG) offers a functional imaging approach for the entire body. ¹⁸FDG-PET is shown to be able to detect various types of tumours, among which HNSCC.⁷ However, false positive results can occur and confirmation of PET findings can be problematic. The current study evaluates the value of ¹⁸FDG-PET in screening for distant metastases in HNSCC patients. The ¹⁸FDG-PET results are compared with the results of chest CT in HNSCC patients with risk factors for distant metastases.