Abstract
BACKGROUND:
Outcomes of patients with metastatic urothelial carcinoma (mUC) with early bone metastases (eBM) vs no early bone metastases (nBM) have not thoroughly been described in the age of immuno-oncology.
OBJECTIVE:
To compare survival and other clinical outcomes in patients with eBM and nBM.
METHODS:
We used a multi-institutional database of patients with mUC treated with systemic therapy. Demographic, metastatic site, treatment patterns, and clinical outcomes were recorded. Wilcoxon rank-sum, chi-square tests were performed. Survival was estimated by Kaplan-Meier method; multivariable Cox analysis was performed.
RESULTS:
We identified 270 pts, 67% men, mean age 69±11 years. At metastatic diagnosis, 27% had≥1 eBM and were more likely to have
CONCLUSIONS:
Patients with mUC and eBM have poorer outcomes, may benefit less from anti-PD-1/PD-L1 therapy and represent an unmet need for novel therapeutic interventions. Dedicated clinical trials, biomarker validation to assist in patient selection, as well as consensus on reporting of non-measurable disease are required.
INTRODUCTION
Patients with urothelial carcinoma (UC) have substantial morbidity and the five-year overall survival (OS) of patients with UC who have distant metastases is unfortunately very low at approximately 5% [1]. In metastatic urothelial carcinoma (mUC), tissue specific tropism has been recognized, and common sites of metastatic spread include both lymph node, visceral organs and bone [2, 3]. Bone metastases may occur in almost 50% of cases and may confer significant morbidity [3]. Hypercalcemia, bone pain, pathologic fractures, and spinal cord compression are well known complications of bone metastases, and unfortunately many patients with mUC require hospitalization to manage related complications [4]. Visceral metastases have classically been defined for clinical trial data collection, as well as for clinical care, collectively to include liver, lung or bone metastases, the presence of metastases to any of these sites has been considered a negative prognostic clinical biomarker [5–8].
Disparate phenotypic metastatic progression patterns, such as the bone-only phenotype, may correspond with UC molecular subtypes and possibly suggest distinctive responses to systemic chemotherapy [2, 9–12]. For most patients, we continue to rely largely on clinical characteristics reflected in available trial data to inform treatment decision making. An elderly patient with mUC and
We sought to evaluate the impact of eBM on OS and other clinical outcomes of patients with mUC treated with systemic therapy at three large academic cancer centers. We hypothesized that eBM would be associated with poorer outcomes vs nBM.
MATERIALS AND METHODS
Patient selection
This retrospective cohort study was conducted at three academic cancer centers in the US, after approval of the institutional review board according to principles by the Declaration of Helsinki (University Hospitals Seidman Cancer Center, #02-14-36; Medical College of Wisconsin, #PRO00035649; University of Washington, #0005690). Patients with mUC diagnosed between March 2005 and August 2019 who received at least one dose of systemic therapy in the metastatic setting were retrospectively identified from the electronic medical record (EMR). All pure urothelial and/or histologic variants were included. Records were reviewed; demographics, clinicopathologic factors, treatment patterns, and OS data were recorded. Imaging studies chosen by the treating physician (CT, bone scan, MRI, or PET) completed prior to initiation of systemic therapy were reviewed, sites of baseline metastatic disease were recorded. The presence of bone lesions on imaging suggestive and/or concerning for metastases as determined by the reading radiologist or those felt to be metastatic by the treating physician were considered positive for bone metastases. Early bone metastases (eBM) was defined as the identification of ≥1 bone metastasis prior to initiation systemic treatment in the metastatic setting; patients who developed bone metastases after the initiation of systemic treatment in the metastatic setting were not included in this definition. Patients with mUC and the absence of early bone metastatic sites were categorized as having nBM. Patients were additionally categorized as having baseline bone only, bone and other non-bone visceral (liver and/or lung), non-bone visceral only, and neither bone nor non-bone visceral metastases. Initial systemic treatment was defined as the first systemic therapy administered in the metastatic setting and recorded and categorized as platinum-based chemotherapy (either cisplatin or carboplatin), ICI, or other (i.e. taxane, gemcitabine, FGFR inhibitor). Patients treated with systemic therapy as part of a clinical trial protocol were included. For patients who received additional lines of systemic therapy, the rationale for changes in treatment were recorded as indicated by the treating physician. Clinical progression was defined as a decline in performance status or development of clinical cancer-related symptoms necessitating a change or hold of systemic treatment. If radiographic progression was identified by the treating physician, the site of progression was recorded as bone, lymph node, lung, liver, CNS or other. Sites of palliative radiation were recorded. Outpatient medication records were reviewed, and maximum prescribed doses of opioid analgesic medications were recorded as morphine milligram equivalents (MME) at the defined oncology visits.
Statistical analysis
Demographic and cancer characteristics were summarized using descriptive statistics and compared between the cohorts using Wilcoxon rank-sum test for continuous and ordinal measures and chi-square tests for categorical outcomes. Patients were followed for OS from the time of the initial systemic treatment in the metastatic setting to death or last follow-up. Follow-up was administratively censored at 36 months due to the small number of patients under follow-up beyond that point. OS curves were estimated using Kaplan-Meier methods, and compared between groups via the log-rank test. Cox regression was used for the multivariable analysis of survival. Analyses were performed using SAS 9.4 (SAS Institute, Cary, NC).
RESULTS
Patient characteristics
Characteristics of the patient cohorts are listed in Table 1. Overall, 270 patients were identified, 67% men (
Demographic, Baseline and Treatment Characteristics
∗NAC=Neoadjuvant Chemotherapy; †TTM = Time from definitive surgery to metastases development in months; ‡Metastatic disease may have been identified in more than one site with exception of lymph node only; §ECOG Performance Status at start of initial treatment, missing 17% of data
Patterns of metastatic progression
At the time of metastatic disease diagnosis, 27% (
Patterns of Disease Progression
∗Progressive disease may have been identified in more than one site
Opioid and palliative radiation outcomes
Patients with eBM were prescribed higher opioid analgesic doses compared to patients with nBM at the time of their first vs last outpatient oncology visit: MME of 60 mg±91 mg vs 28 mg±65 mg (
Sixty-three percent (
Overall survival (OS)
The median OS from the start of initial systemic therapy in the metastatic setting was 11.5 months (95% CI: 9.3–12.9) for the entire cohort, median length of follow up was 18.4 months (0.5 –36). Patients with eBM had significantly shorter OS than those with nBM (median 6.1 vs 13.7 months,

Kaplan- Meier Overall Survival. A. Overall survival for the entire cohort was 11.5 months; B. Overall survival for patients with early bone metastases versus no bone metastases. Median overall survival was 6.1 versus 13.7 months (
Multivariate analysis controlling for age, sex, smoking history, site of primary tumor, histology, presence of
Multivariable Cox Regression Analysis for Overall Survival
eBM, early bone metastases; CPI, checkpoint inhibitor; HR, hazard ratio; CI, confidence interval
OS comparisons between initial systemic therapy regimens for metastatic disease in patients with eBM demonstrated shorter OS for those who received ICI (

Overall Survival Comparisons by Initial Treatment. A. Early Bone Metastases (eBM); For patients with eBM treated with immune checkpoint inhibitors versus platinum, overall survival was 1.6 vs 9.1 months (
DISCUSSION
Multiple prognostic models have identified the presence of visceral metastases as a negative prognostic biomarker, and historically, bone metastases have been included in the definition of visceral metastases along with liver and lung metastases [3, 5–7]. Our study found that the presence of eBM, independent of other sites of metastases, was associated with a 7.6-month decrease in median OS when compared to patients with nBM and a 2.5-fold increase in the risk of death. Lung metastases were not associated with increased risk, a finding which has previously been reported by other groups [13, 14]. These results suggest that eBM is a biomarker of poor prognosis. Lung, liver, and bone metastatic sites may represent differing underlying biology or tumor microenvironment, and therapeutic responses may differ across sites of metastases; a hypothesis which should be tested in future prognostic models.
Additionally, we demonstrated that those patients with eBM had longer OS when treated with initial platinum-based chemotherapy regimens in the metastatic setting when compared to those who received ICI. Although the number of patients within this subset is small, and there are selection and confounding biases in this retrospective cohort study, this represents an intriguing hypothesis which deserves further investigation. It is also interesting to investigate whether or not ICI therapy is beneficial in patients with tumor progression within the bone microenvironment. In other tumor types, such as non-small cell lung cancer, patients with bone metastases when compared to patients without bone metastases have also demonstrated inferior responses to ICI [15, 16]. The efficacy of ICI in patients with mUC and bone metastases is not well understood, and our data support the need for further research on the bone marrow niche, host immune-tumor microenvironment, and molecular mechanisms.
Recently Khaki et al. demonstrated that patients with poor performance status (ECOG 2-3) may have shorter OS when treated with ICI in the first-line setting vs. those with ECOG PS 0-1; however, differences in ECOG PS at the time of initiation of systemic therapy between patients with eBM and those with nBM approached but did not reach statistical significance in our study [17]. The presence of eBM was associated with a similar increase in risk of death as that of ECOG performance status ≥2, demonstrating the significant prognostic impact of early bone metastases. After adjusting for ECOG performance status and other factors, eBM remained a significant independent negative prognostic factor in multivariate analysis.
This study is the first to report on survival and pain outcomes of patients with eBM who received immune checkpoint inhibitors as an initial systemic therapy in the metastatic setting. Few publications exist in the pre-immune checkpoint era which address outcomes of patients with mUC and early bone metastases. A population-based study utilizing the National Cancer Institute Surveillance, Epidemiology and End Results (SEER) database demonstrated similarly poor median OS of just 4 months in patients with bone metastases at diagnosis [18]. Necchi et al. evaluated outcomes in the subgroup of patients with mUC with exclusive bone metastases compared to those with no bone metastases and both bone and other sites of metastases [2]. Similar to our findings, patients with bone metastasis had worse prognosis irrespective of other sites of disease. For patients with bone-only metastatic sites, median OS was 14.4 months, those with bone and other metastatic sites had median OS of 12 months [2]. In patients who received first-line platinum-based chemotherapy, the presence of bone metastases was associated with lower response rate to chemotherapy [2].
Patients with mUC have multiple sources of morbidity due to prior chemotherapy, past surgeries, as well as metastatic disease burden, all of which may impact a patient’s functional status and, ultimately, treatment options. Bone metastases specifically may lead to bone-related pain, pathologic fractures, hypercalcemia, and epidural spinal cord compression. We demonstrated that patients with eBM were more likely to present with
These inferior pain and symptom control findings amongst those with eBM impact quality of life, performance status, and ability to participate in clinical trials especially whose criteria restrict candidate patients who have escalating pain or analgesia requirements, radiation washout periods, or concurrent radiation. Prospective trials that include palliative care intervention and patient reported outcome endpoints in bladder cancer in the era of immuno-oncology and antibody-drug conjugates are needed. Intervention trials have often excluded patients with mUC who have bone progression due to non-measurable disease status, poor prognosis, escalating pain, or poor performance status. An urgent need amongst the bladder cancer research community is for development of consensus for inclusion criteria that reconciles the current knowledge- and access-gaps for those with non-measurable disease, as well as for reporting outcomes of patients with non-measurable disease.
This study reports on a multi-institutional dataset and large patient cohort outside the filter of clinical trials. Our study analyzed OS from initiation of systemic therapy in the metastatic setting and thus is not confounded by prior therapies in the metastatic setting. The specific effect of subsequent treatments is hard to quantify in this analysis. The recent FDA approval of switch maintenance avelumab after platinum-based chemotherapy, current FDA approved salvage therapies after chemotherapy and ICI (enfortumab-vedotin and erdafitinib), as well as other non-FDA approved therapies may impact survival and/or other clinical outcomes [19–25].
Limitations of our study include its retrospective design in only three academic centers with moderate sample size, potential heterogeneity in data extraction, missing data, selection and confounding biases, as well as lack of randomization, standardized baseline imaging and centralized radiographic review. There was also variability in therapy selection, intervals of assessment and follow up times. There was no assessment of PD-L1 status, other molecular or laboratory biomarkers. We did not identify those patients who were cisplatin eligible vs. ineligible. We did not measure progression-free survival, cancer-specific survival, toxicities and overall response rate to a particular therapy, bone fractures and other skeletal related events. Despite these certain limitations, this study generated several intriguing hypotheses and supports further assessment of this important patient population.
In conclusion, we define eBM as the presence of at least one identified metastatic bone lesion before initiation of systemic therapy in the metastatic setting. The presence of eBM was associated with poor response to treatment, need for escalated palliative measures, and early death compared to patients with nBM. It is likely that this clinical phenotype will be further understood with molecular profiling and subtyping. Tumor tissue correlatives and incorporation of stratification based on osseous involvement in trials can further enhance our understanding of the mechanisms underlying bone and other metastatic site tropism. Consensus for inclusion and reporting of patients’ non-measurable disease, as well as palliative care endpoints, should be developed and incorporated into clinical trial design.
Footnotes
ACKNOWLEDGMENTS
The authors have no acknowledgments.
FUNDING
The authors report no funding.
AUTHOR CONTRIBUTIONS
AN: Conception, performance of data collection, interpretation of data and writing the article; RC: Performance of data collection; EL: Performance of data collection; AS: Analysis of data; AK: Performance of data collection; LD: Performance of data collection; PG: Writing the article; BN: Performance of data collection and writing the article; GM: Performance of data collection and writing the article; TZ: Writing the article; CH: Conception, interpretation of data and writing the article.
CONFLICT OF INTEREST
AA Nelson has no conflicts of interest to report; RJ Cronk has no conflicts of interest to report; EA Lemke has no conflicts of interest to report; A Szabo has no conflicts of interest to report; AR Khaki has previously owned stocks in Merck and Sanofi, sold as of 4/28/20. LN Diamantopoulos has no conflicts of interest to report; P Grivas: (all unrelated in the last 3 years): consulting for AstraZeneca, Bayer, Bristol-Myers Squibb, Clovis Oncology, Driver, EMD Serono, Exelixis, Foundation Medicine, GlaxoSmithKline, Genentech, Genzyme, Heron Therapeutics, Janssen, Merck, Mirati Therapeutics, Pfizer, Roche, Seattle Genetics, QED Therapeutics; participation in educational program for Bristol-Myers Squibb; and institutional research funding from AstraZeneca, Bavarian Nordic, Bayer, Bristol-Myers Squibb, Clovis Oncology, Debiopharm, Genentech, Immunomedics, Kure It Cancer Research, Merck, Mirati Therapeutics, Oncogenex, Pfizer, QED Therapeutics. BG Nezami has no conflicts of interest to report; GT MacLennan has no conflicts of interest to report; T Zhang: research funding (to Duke) from Pfizer, Janssen, Acerta, Abbvie, Novartis, Merrimack, OmniSeq, PGDx, Merck, Mirati, Astellas; consulting/speaking with Genentech Roche, Exelixis, Genomic Health, and Sanofi Aventis; and consulting with AstraZeneca, Bayer, Pfizer, Foundation Medicine, Janssen, Amgen, MJH Associates, and BMS. Stock ownership/employment (spouse) from Capio Biosciences, Archimmune Therapeutics, and Nanorobotics; CJ Hoimes Consult for Merck, Genentech, Seattle Genetics.
