Survival of Patients with Oligometastases Treated with Palliative Intent

Background: The clinical distinction between oligometastatic (OM) and polymetastatic (PM) disease suggests different survival trajectories, yet definitions of OM remain inconsistent. With few exceptions, conventionally fractionated palliative-intent radiotherapy (PRT) is not expected to improve survival. We report the prevalence of OM, compare survival between OM and PM cohorts receiving PRT, and evaluate the accuracy of clinician survival predictions in a population treated with conventional PRT. Methods: We retrospectively reviewed prospectively collected data on 952 patients with incurable cancer referred to our tertiary cancer center’s Palliative Radiation Oncology or Palliative Care programs (June 2010–December 2014). Patients were categorized as OM (maximum five metastases and three organs) or PM based on 2019 international consensus guidelines. Summary statistics were calculated. Actual survival was analyzed using Kaplan–Meier estimates. The Cox Proportional Hazards (HR) model was used to obtain unadjusted and adjusted HR, as well as to identify prognostic variables. Results: Of the 952 patients, 209 (21.95%) were OM. Chest (817/1223), abdominal (799/1108), and soft tissue/lymph node (1033/1349) metastases were more likely to be detected by screening, while brain metastases (122/884) were less likely. Median actual survival was significantly longer for OM compared to PM (201 vs. 109 days, p < 0.0001). Healthcare providers significantly underestimated the actual survival of OM patients. In the unadjusted analysis, PM was associated with poorer OS compared with OM (HR 1.59; 95%CI 1.35–1.86). This association remained significant in the multivariable analysis, where patients with PM had an 89% higher risk of death than those with OM (HR 1.89; 95%CI 1.47–2.43). Other factors independently associated with poorer survival included age ≥ 65 years, gastrointestinal or lung cancer, and two or more metastatic sites. Conclusions: Patients with OM demonstrate an inherent survival advantage over those with PM, likely driven by favorable tumor biology and patient-specific factors. Provider prognostic bias frequently underestimates OM survival, which may inadvertently restrict appropriate patient referrals and therefore access to potentially beneficial locally ablative therapies. Objective clinical criteria that consider this lead time bias must drive treatment decisions to appropriately guide management in patients with oligometastatic disease.