Oligometastatic prostate cancer: definitions, clinical outcomes, and treatment considerations

Abstract

The oligometastatic state has been proposed as an intermediate stage of cancer spread between localized disease and widespread metastases. With improvements in diagnostic modalities such as functional imaging, oligometastatic prostate cancer is being diagnosed with greater frequency than ever before. Furthermore, the paradigm for treatment of advanced prostate cancers is shifting toward a more aggressive approach. Many questions surround the understanding of the process and consequences of oligometastasis, meaning that the contemporary literature offers a wide variety of definitions of oligometastatic prostate cancer. Until genomic data exist to provide a biological component to the definition of oligometastatic disease, a clinical diagnosis made on the basis of up to five extrapelvic lesions is reasonable for use. Retrospective studies suggest that interventions such as radical prostatectomy and local or metastasis-directed radiotherapy can be performed in the metastatic setting with minimal risk of toxic effects. These therapies seem to decrease the need for subsequent palliative interventions, but insufficient data are available to draw reliable conclusions regarding their effect on survival. Thus, a protocol for clinicians to manage the patient presenting with oligometastatic prostate cancer would be a useful clinical tool.

Figure 1. Recurrent prostate cancer detected with PSMA-targeted ¹⁸F-DCFPyL PET–CT

The patient presented approximately 5 years after radical prostatectomy with a serum PSA of 0.43 ng/ml and without evidence of disease on bone scan or contrast-enhanced CT. The (a) maximal intensity projection and (b) fused PET–CT axial images demonstrate recurrent disease in the transverse process of T7 (red arrows). The patient was successfully treated with stereotactic body radiation to the lesion.

Figure 2. Schema for the phase II Randomized Observation versus Stereotactic Ablative RadiatIon for OLigometastatic Prostate CancEr (ORIOLE) trial

Men with metachronous hormone-naive oligometastatic disease will be enrolled and dynamically randomized to the schema as shown. AP, alkaline phosphatase; CTCs, circulating tumour cells; ctDNA, cell-free circulating tumour DNA; LDH, lactate dehydrogenase; PBMC, peripheral blood mononuclear cells; SABR, stereotactic ablative radiation; SBRT, stereotactic radiation therapy; T, serum testosterone. ORIOLE is sponsored by the National Cancer Institute (NCI) 1U01CA183031 and a Movember-PCF Challenge Award.