F-18 FDG-PET/CT imaging is a better choice than ultrasound for detecting both lymph node and abdominal metastases in patients with malignant melanoma, Swiss investigators have found.
Due to F-18 FDG-PET/CT's higher sensitivity and because it detected additional metastatic lesions throughout the body, the modality has an edge over ultrasound, which is typically used to identify metastases in this type of cancer, a team led by Dr. Philipp Weber wrote. "F-18 FDG PET/CT is preferable to ultrasound for detecting both lymph node and abdominal metastases."
Malignant melanoma has steadily increased in Switzerland. The incidence among men has grown by 83.3% since the late 1980s and among women by 63.5%, according to the researchers. Determining which imaging modality offers the highest sensitivity and specificity for primary staging and restaging is crucial, they noted.
In this study, Weber and colleagues included 308 patients who underwent one or more F-18 FDG-PET/CT scan and/or one or more ultrasound exams for primary staging or restaging of suspected or confirmed metastatic melanoma between September 1998 and August 2014 for primary staging or restaging of suspected or confirmed metastatic melanoma. The results were published on 21 October in Medicine.
Overall, F-18 FDG-PET/CT identified 824 cancer lesions and ultrasound identified 726. On a per-exam basis, an analysis revealed significant differences for the sensitivity of F-18 FDG PET/CT (80%) compared to whole ultrasound (63%) and peripheral lymph node ultrasound (61%). PET/CT's specificity was slightly lower compared with ultrasound, however, at 96% versus 98% for whole ultrasound and 99% for abdominal ultrasound, the researchers reported.
Lymph node metastasis inguinal right. (A) Detected as true positive by F-18 FDG-PET/CT. (B) Not evaluated as lymph node by ultrasound (false negative). Image courtesy of Medicine.Weber and colleagues noted that at their clinic in Basel, patients with malignant melanoma have undergone a combined examination with both modalities for several years. But in addition to being more accurate, using F-18 FDG-PET/CT alone may save costs, and they plan to use the study results to inform their practice, they wrote.
"Based on the available data from this study, the use of [abdomen ultrasound] cannot be justified, neither as a sole application, nor in combination with F-18 FDG-PET/CT," the group concluded.
![Examples of ultrasound findings and techniques. (A) Images in a 39-year-old male patient with a mass in the left thigh. The mass is heterogeneous on the B-mode US image (compared with the patient in D) and showed increased microvascularity (superb microvascular imaging [SMI]) and shear-wave elastography (SWE) values. Undifferentiated pleomorphic sarcoma was diagnosed at biopsy (with pleomorphic rhabdomyosarcoma in surgical specimen). (B) Images in an 18-year-old male patient with a mass in the left leg. The mass is hypoechoic on the B-mode image, with no other findings suggestive of malignancy. The lesion is in contact with the cortex of the tibia, which is slightly irregular. CT revealed a doubtful anteromedial tibial erosion. The microvascular study demonstrated high vascularization, suggestive of malignancy. Periosteal Ewing sarcoma was diagnosed with both histologic and immunohistochemical confirmation. (C) Images in a 69-year-old female patient with a lump growing on the outside of the left leg. Multiple SWE examinations were performed (please note the high values obtained in the measurements, whereas the color map highlights the stiffness relative to adjacent tissues). SMI showed areas of increased vascularization to target for sampling. Undifferentiated spindle cell sarcoma was diagnosed at biopsy, with residual leiomyosarcoma in the surgical specimen after neoadjuvant therapy. (D) Images in a 56-year-old female patient with a mass in the right thigh. The mass is heterogeneous at both B-mode ultrasound (similar to patient A) and MRI (coronal T2-weighted spectral attenuated inversion recovery [SPAIR]; T1-weighted pre-contrast and postcontrast imaging), which even shows uptake after the administration of paramagnetic contrast material, which is traditionally suggestive of malignancy. Low values at SMI and elastography are suggestive of benignity. Spindle cell lipoma was diagnosed at biopsy, with atypical spindle cell lipomatous tumor in the surgical specimen.](https://img.auntminnieeurope.com/mindful/smg/workspaces/default/uploads/2026/08/images-radiol250278fig2.APCFLSvX6p.jpg?auto=format%2Ccompress&fit=crop&h=100&q=70&w=100)
![Examples of ultrasound findings and techniques. (A) Images in a 39-year-old male patient with a mass in the left thigh. The mass is heterogeneous on the B-mode US image (compared with the patient in D) and showed increased microvascularity (superb microvascular imaging [SMI]) and shear-wave elastography (SWE) values. Undifferentiated pleomorphic sarcoma was diagnosed at biopsy (with pleomorphic rhabdomyosarcoma in surgical specimen). (B) Images in an 18-year-old male patient with a mass in the left leg. The mass is hypoechoic on the B-mode image, with no other findings suggestive of malignancy. The lesion is in contact with the cortex of the tibia, which is slightly irregular. CT revealed a doubtful anteromedial tibial erosion. The microvascular study demonstrated high vascularization, suggestive of malignancy. Periosteal Ewing sarcoma was diagnosed with both histologic and immunohistochemical confirmation. (C) Images in a 69-year-old female patient with a lump growing on the outside of the left leg. Multiple SWE examinations were performed (please note the high values obtained in the measurements, whereas the color map highlights the stiffness relative to adjacent tissues). SMI showed areas of increased vascularization to target for sampling. Undifferentiated spindle cell sarcoma was diagnosed at biopsy, with residual leiomyosarcoma in the surgical specimen after neoadjuvant therapy. (D) Images in a 56-year-old female patient with a mass in the right thigh. The mass is heterogeneous at both B-mode ultrasound (similar to patient A) and MRI (coronal T2-weighted spectral attenuated inversion recovery [SPAIR]; T1-weighted pre-contrast and postcontrast imaging), which even shows uptake after the administration of paramagnetic contrast material, which is traditionally suggestive of malignancy. Low values at SMI and elastography are suggestive of benignity. Spindle cell lipoma was diagnosed at biopsy, with atypical spindle cell lipomatous tumor in the surgical specimen.](https://img.auntminnieeurope.com/mindful/smg/workspaces/default/uploads/2026/08/images-radiol250278fig2.APCFLSvX6p.jpg?auto=format%2Ccompress&dpr=2&fit=crop&h=167&q=70&w=250)
