Can a Nomogram Help to Predict the Overall and Cancer-specific Survival of Patients With Chondrosarcoma?

BACKGROUND

Many factors have been reported to be associated with the prognosis of patients with chondrosarcoma, but clinicians have few tools to estimate precisely an individual patient's likelihood of surviving the illness. We therefore sought to develop effective nomograms to better estimate the survival of patients with chondrosarcoma.

QUESTIONS/PURPOSES: (1) Which clinicopathologic features are independent prognostic factors for patients with chondrosarcoma? (2) Can we develop a nomogram to predict 3- and 5-year overall and cancer-specific survival of individual patients with chondrosarcoma based on personalized information?

METHODS

We collected information on patients diagnosed with chondrosarcoma between 1988 and 2011 from the Surveillance, Epidemiology, and End Results (SEER) database. The SEER database consists of 18 cancer registries and covers approximately 30% of the total United States population. One thousand thirty-four adult patients with grade II or III chondrosarcoma were included in the cohort (patients with grade I chondrosarcoma were not evaluated in this study), while 327 patients were excluded from the study owing to missing data regarding tumor size or metastasis. Nine hundred nineteen patients (89%) in the cohort had complete followup for at least 1 year. The X-tile program was used to determine optimal cutoff points. Univariate and multivariate analyses were applied to identify independent factors that were further included in the nomograms predicting 3- and 5-year overall survival and cancer-specific survival. Records of 1034 patients were collected and randomly divided into training (n = 517) and validation (n = 517) cohorts. The nomograms were developed based on training cohort. Data for the training cohort were obtained for internal validation of the nomograms, whereas data for the validation cohort were obtained for external validation of the nomograms. Bootstrapped validation, which used a resample with 500 iterations, was applied to validate the nomograms internally and externally.

RESULTS

Six independent prognostic factors for overall survival and six for cancer-specific survival were identified and incorporated to construct nomograms for 3- and 5-year overall and cancer-specific survival. These nomograms can easily be used by providers in the office to estimate a patient's prognosis; the only clinical details a provider needs to use these nomograms effectively are age, histologic subtype, tumor grade, whether surgery was performed, tumor size, and the presence or absence of metastases. Internal and external calibration plots for the probability of 3- and 5-year overall survival and cancer-specific survival showed good agreement between nomogram prediction and observed outcomes. The concordance indices (C-indices) for internal validation of overall survival and cancer-specific survival prediction were 0.803 and 0.829, respectively, whereas the C-indices for external validation were 0.753 and 0.759, respectively.

CONCLUSIONS

We were able to develop effective nomograms to predict overall survival and cancer-specific survival for patients with chondrosarcoma; these nomograms require only basic information, which should be available to all providers in the office setting. If these observations can be validated in different registries or databases, the nomograms can assist clinicians in counseling patients regarding therapeutic choices.

LEVEL OF EVIDENCE

Level III, prognostic study.