Background & relevance
Oligometastatic PCa is a heterogeneous disease state which is poorly understood and of which the clinical implications are unclear. The concept ‘oligometastatic disease’ has been proposed as an intermediate stage between localised disease and widespread metastases. Oligometastatic disease might be amenable to targeted metastasis-directed therapy to prevent the development of further disease spread, to delay systemic therapy and possibly to improve overall survival [1]. Tumours giving rise to oligometastatic disease might be biologically and genetically different from tumours that induce widely metastatic disease, however, this is not yet well understood.
Currently there is no consensus on the imaging modalities used for its detection and there is a lack of uniformity in describing the condition [2,3]:
- Number of metastases: usually up to 5
- Number of involved sites: usually up to 2
- Synchronous (de novo or primary metastases, untreated primary tumour) versus metachronous disease (primary tumour previously treated in non-metastatic setting and metastases are encountered during recurrence)
- Oligorecurrence versus oligoprogression versus oligopersistence
- Hormone-sensitive versus castration-resistant disease state.
A characterisation of oligometastatic disease based on 5 developmental factors was suggested following a consensus meeting, however, this needs to be further evaluated to assess its prognostic value and acceptance and compliance in clinical practice [2].
For all cases, it is assumed that the location of metastases does not rule out metastasis-directed therapy.