Hazards for pain severity and pain interference with daily living, with exploration of brief pain inventory cutpoints, among women with metastatic breast cancer.

Few longitudinal studies have assessed risk factors for pain outcomes in tumor-specific populations. Such studies are needed to improve clinical practice guidelines for cancer pain management over the course of treatment. Among patients with metastatic breast cancer, we assessed the impact of baseline clinical and demographic risk factors on patients reaching different pain severity and interference scores. We analyzed data originally collected in a clinical trial of two bisphosphonate therapies. Pain was measured by the Brief Pain Inventory (BPI) severity and interference with daily living 0-10 subscales. We fit univariate (per-cutpoint) and multivariate (cutpoints 3, 4, 5, 6, and 7 on the BPI) proportional hazards models to identify predictors of pain outcomes over 51 weeks among 1,124 women with metastatic breast cancer. Predictors included race, age, education, geographic region, performance status, chemotherapy versus hormonal therapy only, time from first bone metastasis to randomization, and previous skeletal-related event (SRE, e.g., fractures, spinal cord compression). Non-Caucasian women had greater hazards for reaching higher cutpoints (5 and above) on the severity scale than Caucasian women (hazard ratio [HR] for cutpoint 5 interaction term=1.76; 95% confidence interval [CI]=1.37-2.26). For the interference scale, these hazards were greater for those patients with restricted (versus active) baseline Eastern Cooperative Oncology Group (ECOG) performance status (HR for cutpoint 5 interaction term=2.51; 95% CI=2.01-3.13). In the multivariate severity model, other factors associated with higher pain severity were restricted baseline ECOG performance status, previous SRE, and not being employed full-time at baseline (HRs=1.70, 1.23, and 1.33, respectively). Our findings that non-Caucasian race and restricted performance status were associated with greater pain hazards over time confirm previous cross-sectional findings that these characteristics are pain risk factors. Because we found that the most influential demographic and clinical baseline factors had predictive value for worsening outcomes as early as cutpoint 5, we recommend that pain management strategies use cutpoints informed by risk factors for worsening outcomes as cues for earlier intervention, thus delaying or preventing worst pain among women with metastatic disease who are at greatest risk.