Evaluation of positron emission tomography imaging to detect lymph node metastases in patients with high-risk cutaneous squamous cell carcinoma

Ten to twenty percent of high-risk cutaneous squamous cell carcinoma (cSCC) can metastasize to regional lymph nodes. Detection of nodal metastasis is mandatory to manage high-risk cSCC. This study was aimed to evaluate the 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) imaging to assess lymph node (LN) metastasis of high-risk cSCC patients. Twenty-six patients with histologically proven primary cSCC were enrolled. All patients underwent whole-body PET prior to lymphoscintigraphy and subsequent sentinel LN biopsy. The maximum standardized uptake value (SUVmax) of more than 2.5 is generally evaluated as a positive PET finding indicative of malignancy. On the basis of the histopathological and PET findings, 30 LN from 26 patients were categorized into four groups: (i) histologically negative and PET negative (true-negative; n = 22); (ii) histologically positive and PET negative (false-negative; n = 0); (iii) histologically positive and PET positive (true-positive; n = 3); and (iv) histologically negative and PET positive (false-positive; n = 5). The mean SUVmax was significantly higher in the true-positive cases (11.0 ± 2.8) than in the false-positive cases (3.4 ± 0.6). In the false-positive cases, the number of tumor-infiltrating inflammatory cells at the primary skin site was highest among the four groups, suggesting that inflammation contributed to the false-positive uptake of FDG. Although we cannot negate the possibility of the presence of PET-undetectable micrometastasis, the SUVmax value may be useful for avoidance of excess performance of sentinel LN biopsy.