Defining Oligometastatic Bladder Cancer: A Systematic Review.

Context: Unlike other cancers, the concept of oligometastatic disease (OMD) in bladder cancer (BC) has not been systematically investigated. There is therefore a need to develop universally accepted definitions and guidelines for the management of oligometastatic BC (OMBC). Objective: To conduct a systematic review to assist a European consensus group in producing a definition of OMBC and to provide recommendations on staging and local therapies. Evidence acquisition: The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement was followed. Abstracts for articles focused on BC that addressed the issue of OMBC and provided a definition of oligometastatic status were selected. We collected data on the number of metastases, the number of metastases per organ, the number of organs involved, and metastatic sites that were excluded. Evidence synthesis: Sixteen eligible articles were retrieved (9 retrospective series involving 330 patients, 4 reviews, 1 consensus statement, 1 guideline paper, and 1 ongoing prospective phase 2 trial). A maximum of three to five metastatic lesions were compatible with the definition of OMBC. The number of organs involved and lesion size were not universally included in the OMBC definitions. OMD categories studied included synchronous OMBC, oligorecurrence, and oligoprogression. Conclusions: There is little information on OMBC in the literature. Our systematic review revealed that only three to five metastatic sites amenable to surgery or radiotherapy that respond to systemic therapy is the setting most frequently chosen for a combination of systemic treatment and metastases-directed therapy. This setting could represent a basis for future prospective studies on OMBC. Patient summary: Oligometastatic bladder cancer is a disease state in which favorable outcomes can be expected after a treatment combination of systemic therapy, plus surgery and/or radiotherapy for sites of bladder cancer metastasis. Our systematic review showed a lack of meaningful evidence to define this disease state. There is an urgent need to develop organized research in this field.