Rural-Urban Disparities in Survival Among Patients With Malignant Primary Osseous Neoplasms of the Spine and Sacropelvis: A Population-Based Cohort Study.

Background Malignant primary osseous neoplasms of the spine and sacropelvis are rare tumors whose outcomes rely heavily on specialized, guideline-driven care, which is concentrated in metropolitan referral centers. Investigations of rurality in this population have been limited by single-histology cohorts, small numbers of rural patients, and unadjusted comparisons, and none have weighed geographic disadvantage directly against the socioeconomic conditions with which it coexists. This study aimed to determine whether rural residence is independently associated with overall survival and cause-specific survival, and secondarily whether county-level median household income is independently associated with survival in the same models. Methodology This was a retrospective, population-based cohort study using the Surveillance, Epidemiology, and End Results (SEER) database from 2000 to 2023. Patients with microscopically confirmed malignant chordoma, chondrosarcoma, osteosarcoma, or Ewing sarcoma of the vertebral column or the pelvic bones, sacrum, or coccyx with known survival time were included. Rurality was defined using SEER county attributes, with nonmetropolitan counties classified as rural. Multivariable Cox proportional hazards models for overall survival and cause-specific survival were adjusted for demographic, socioeconomic, tumor, and treatment characteristics, with time-based interaction terms added where Schoenfeld residuals indicated violation of the proportional hazards assumption. Results Of 3,631 patients (median age = 51 years; 59% male), 3,255 (90%) resided in urban counties and 376 (10%) in rural counties. Rural residence was concentrated in low-income counties (54% below $60,000 vs. 4.1% of urban patients). Rurality was not independently associated with overall survival (hazard ratio (HR) = 0.95, 95% CI (confidence interval) = 0.82-1.09; p = 0.449) or cause-specific survival (HR = 0.94, 95% CI = 0.80-1.11; p = 0.457). County income showed a graded association with overall survival relative to counties below $60,000, with HRs of 0.82 ($80,000-$100,000), 0.72 ($100,000-$120,000), and 0.68 (>$120,000), all with p-values <0.001, and no difference for $60,000-$80,000 (HR = 1.01). A similar gradient was observed for cause-specific survival. Surgery was associated with lower mortality (overall survival: HR = 0.76; cause-specific survival: HR = 0.80; both p < 0.001), whereas radiotherapy was not. Unadjusted differences by rurality in stage at presentation and treatment receipt were small. Conclusions Rural residence conferred no independent survival disadvantage once socioeconomic and clinical factors were accounted for, whereas county-level income remained independently associated with mortality in a graded fashion. Because rural residence and low county income overlap heavily in this cohort, the survival signal appears to be carried by socioeconomic context rather than by geography. These tumors are rare, are not amenable to screening, and are largely managed at specialized referral centers, which may explain the absence of the rural disadvantage described for screen-detectable cancers. Identifying at-risk patients by geography alone may overlook socioeconomically disadvantaged patients in urban counties, and direct assessment of financial and access-related barriers may be more informative than rural-urban classification.