Essential Roles of Positron Emission Tomography-Computed Tomography Scan for Detection of Occult Secondary Tumor

BACKGROUND: Oral squamous cell carcinoma (OSCC) is the most prevalent oral malignancy, often requiring precise staging due to the poor prognosis associated with distant metastasis. While conventional imaging, such as computed tomography (CT) and magnetic resonance imaging (MRI), is the standard for evaluating local tumor status, these modalities have limitations in detecting occult secondary tumors. CASE PRESENTATIONS: Two representative clinical cases were retrospectively evaluated. A 22-year-old female patient was initially diagnosed with metastatic oral cancer, following the revelation of an occult primary renal cell carcinoma using positron emission tomography-computed tomography (PET-CT) and biopsy. The second case involved a 65-year-old woman in whom PET-CT revealed a synchronous endometrial carcinoma coexisting with maxillary OSCC, facilitating timely intervention for both primary tumors. DISCUSSION: Despite its strengths in whole-body metabolic staging and efficient detection of occult secondary tumors, PET-CT has limitations, including false-positive findings from inflammation, false negatives in small or low-avidity lesions, and technical artifacts from dental metal. Emerging hybrid positron emission tomography-magnetic resonance (PET-MR) imaging technology shows promise in overcoming these limitations by combining metabolic data with superior soft-tissue contrast. CONCLUSION: PET-CT is a valuable multimodal imaging strategy that improves identification of unexpected findings in oral malignancies, though its results must be carefully integrated with clinical and histopathologic data.