Predictive Factors for Failed Nonsurgical Management of Long Bone Metastasis and Myeloma.

Background: Understanding the risk factors for failing nonsurgical management of metastatic bone disease is necessary to determine those patients who will benefit from prophylactic stabilization; however, standard predictive models do not include several clinically relevant factors. The primary and secondary objectives of this study were to evaluate comprehensive patient- and disease-related factors as potential predictors of failure of radiation therapy alone for long bone lesions and overall survival in metastatic disease and myeloma.

Methods: All patients who underwent radiation therapy for long bone metastases at our tertiary care institution from May 2011 to February 2020 were retrospectively reviewed. Of 475 lesions, we excluded those with prophylactic fixation or fracture before radiation therapy, and those <0.5 cm on plain radiographs. Outcomes of the 186 lesions were classified as no progression, progression requiring prophylactic fixation, or progression to pathologic fracture. Blinded radiograph review was done by two orthopaedic oncology surgeons and two musculoskeletal radiologists. Demographic, socioeconomic, lesion, cancer severity, and patient-specific risk factors were identified, and potential predictors were analyzed using backwards stepwise regression.

Results: Following radiation therapy, 8.6% lesions underwent prophylactic fixation and 14.0% fractured. Prophylactic fixation was associated with Mirels' score (OR = 1.98, P = 0.025), lesion cortical involvement (OR = 16.96, P = 0.010), and younger patient age (OR = 0.93, P = 0.024). Fracture was associated with lesion cortical involvement (OR = 10.16, P = 0.003) and "low risk" histology (OR = 9.01, P = 0.057). Orthopaedic treatment (either prophylactic surgery or pathologic fracture management) was associated with Mirels' score (OR = 1.62, P = 0.015), lesion cortical involvement (OR = 8.94, P = 0.002), humerus location (OR = 4.19, P = 0.042), and Medicare (OR = 4.12, P = 0.062) or private insurance (OR = 5.69, P = 0.022) compared with Medicaid. ECOG score (OR = 1.28, P = 0.003) was found to be a risk factor for increased mortality after radiotherapy, while "low risk" histology (OR = 0.51, P = 0.029), mixed lesion type (OR = 0.34, P = 0.006), and increased body mass index (OR = 0.95, P = 0.001) were protective factors.

Conclusions: Radiograph measurements of cortical involvement were the most clinically relevant for determination of metastatic lesion fracture risk; however, predictors of local failure not addressed in Mirels' score should be considered in clinical decisions about prophylactic fixation. Surgery may be underperformed for histologies commonly considered to be "low risk" for local progression after radiation therapy.