Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography (FDG PET/CT) Monitoring of Rapidly Progressive Low-Risk Cutaneous Melanoma: A Case Report of Durable Response to Combined Stereotactic Body Radiotherapy (SBRT) and Immunotherapy

We present a case of metastatic cutaneous melanoma without a BRAF mutation that showed an unusually aggressive disease course despite favorable initial histopathological features. The patient was initially diagnosed with superficial spreading melanoma with a negative sentinel node. After resection of the subcutaneous metastasis, rapid and extensive systemic dissemination occurred within two months. Metastases affected the liver, lungs, bone, soft tissue structures, and a large parailiac tumor. Therapy included combined immunotherapy (pembrolizumab + ipilimumab) and multiple series of stereotactic body radiotherapy (SBRT) for oligometastatic lesions. After an initial mixed response, secondary SBRT resulted in complete metabolic regression of most lesions on fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT). The remaining parailiac remnant showed a gradual decrease in size and metabolic activity during follow-up. Continuous pembrolizumab monotherapy and targeted SBRT provided long-term disease control, with no evidence of active disease on the last FDG PET/CT. This case highlights the heterogeneity of melanoma, the possible limitations of prognostic factors, and the potential role of earlier initiation of systemic therapy and a combined approach of SBRT and immunotherapy in selected patients.