Evaluation of positron emission tomography imaging to detect lymph node metastases in patients with extramammary Paget's disease

Patients with extramammary Paget's disease (EMPD) have a relatively good prognosis, when spread of the tumor cells is limited to the epidermis. However, invasive EMPD has a poor prognosis, when the patients have regional lymph node metastasis. Detection of nodal metastasis is thus mandatory to manage EMPD. To evaluate the ¹⁸ F-fluorodeoxyglucose positron emission tomography (FDG-PET) imaging to assess lymph node metastasis, 15 patients with histologically proven primary EMPD were enrolled in this study. All patients underwent whole-body PET prior to sentinel lymph node biopsy (SLNB). The maximum standardized uptake value (SUVmax) of more than 2.5 was evaluated as positive PET indicative of malignancy. Among 14 cases with the primary genital lesions, 11 cases underwent bilateral SLNB of the inguinal nodal basin and the remaining three cases unilateral SLNB. One case with a primary axillary lesion underwent unilateral SLNB of the axillary nodal basin. Therefore, a total of 26 regional basins were investigated. In general, nodal basins can be categorized into four groups: (i) histologically negative and PET negative (true negative); (ii) histologically positive and PET negative (false negative); (iii) histologically positive and PET positive (true positive); and (iv) histologically negative and PET positive (false positive) groups. In the 26 nodal basins, there were 19 true negative and seven true positive cases, and neither false negative nor false positive cases were observed. The mean SUVmax was significantly higher in the true positive basins (8.03 ± 3.34) than in the true negative basins (0.26 ± 0.56). The SUVmax value may be useful for detection of nodal metastasis.