Noninvasive imaging with thallium‐201 scintigraphy may not correlate with survival in patients with osteosarcoma

Abstract

Histologic response to preoperative chemotherapy is a strong prognostic factor for osteosarcoma (OS). Thallium-201 (Tl-201) scintigraphic response to initial chemotherapy has previously been described as a predictor of histologic response. In the current study, the authors re-examined a series of patients studied using Tl-201 scintigraphy to determine the correlation between changes observed on Tl-201 scintigraphy and event-free survival (EFS). A total of 22 patients with biopsy-proven OS of the extremity underwent Tl-201 imaging before and immediately after preoperative chemotherapy. The maximum pixel counts taken over the tumor divided by those taken of a background region yielded a tumor-to-background ratio (TBR). The percentage of change in the TBR before and after adjuvant chemotherapy, defined as the alteration ratio (AR), was correlated with EFS. The median AR was 85% (range, 28-100%). The 3-year EFS was 0.72 (95% confidence interval [95% CI], 0.48-0.86) and the 5-year EFS was 0.67 (95% CI, 0.43-0.86). There was no association between AR and EFS detected in this cohort (hazard ratio, 0.99; 95% CI, 0.95-1.02 [Somers rank correlation coefficient, 0.15]). Although Tl-201 scintigraphy was used as a tool for the assessment of response to chemotherapy in patients with OS, the AR did not appear to be predictive of EFS in this small group of patients. It is necessary to use the outcome variables of ultimate interest-EFS and overall survival- and not rely on surrogates for outcome to evaluate potential prognostic factors.