Imaging-Based Prevalence of Oligometastatic Disease: A Single-Center Cross-Sectional Study

Oligometastatic disease refers to a distinct state in patients with cancer characterized by a low metastatic burden, with diagnosis being informed by a limited number of distant metastases in radiologic imaging. However, oligometastasis remains poorly understood in terms of its biology and prevalence in the metastatic cascade. In the absence of clinically viable molecular biomarkers, this study examined the prevalence of oligometastasis using oncological imaging.

This study is based on all consecutive [fluorine-18]-fluorodeoxyglucose (FDG)- and [gallium-68]-prostate specific membrane antigen (PSMA)-positron emission tomography (PET) scans conducted at our cancer center between January and December 2020. We identified and analyzed all PET scans from patients with a maximum of 5 distant metastases from a solid malignancy and also reviewed concurrent cranial magnetic resonance imaging (cMRI) imaging in all candidate patients. Data on the number and sites of metastases were extracted from the imaging reports and verified on imaging studies in case of uncertainties.

In total, 7000 PET scans were analyzed, of which 1155 were performed in unique metastatic patients, and 637 patients showed extracranial oligometastatic disease (55%). Concurrent cMRI scans were available for 20% (130/637) of extracranial oligometastatic patients, 36 of which proved to be polymetastatic after combined PET and cMRI analysis. Prevalence of oligometastatic disease was influenced by primary tumor histology and was most frequent in pancreatic, liver and gallbladder cancers (59%), but was least frequent in cancer of unknown primary (26%). In 72% of oligometastatic cases, only 1 or 2 metastases were detected. Bone/soft tissue metastases were the most common sites of distant metastasis (41%). About 75% of patients had metachronous oligometastatic disease.

Our analysis suggests that about half of patients with metastatic cancer are characterized by a limited tumor burden detectable on PET and cMRI imaging. This finding warrants intensified research efforts to better understand the biology of oligometastatic disease and to optimize multidisciplinary treatment strategies.