br Identifying prognostic factors for patients with
Identifying prognostic factors for patients with chordoma is a significant part of treatment planning. Previous studies have proved that C11 BODIPY 581/591 and surgical margin are independent prognostic factors for patients with chordoma [10-12]. In addition, patient age, recurrence, and tumor size have also been shown to influence patient survival [10-14]. However, single prognostic factors exert limited influence on a precise individualized prediction of prognosis. The prognostic nomogram is an efficient statistical tool that has been suggested as a new standard to predict an individual patient’s survival. And, this graphic calculating scales method has been proved to be a useful method in the management of several types of cancer [15-17]. The obvious advantages of prognostic nomograms are robustness and better predictive accuracy, which enhance its potential for the predictive accuracy of individual prognosis . However, a prognostic nomogram that can be applied to predict the overall survival (OS) and cancer-specific survival (CSS) of patients with chordoma has not been reported, and this might be ascribed to the limited number of chordoma cases in a single institution .
In the present study, the clinical information of patients with chordoma of the skull base, vertebral column, and pelvis between 1973 and 2013 were collected from the Surveillance, Epidemiology and End Results (SEER) dataset and analyzed. SEER is a US population-based cancer database that contains approximately 28% of the overall US population  and collects clinical information of tumor patients in 18 registries in
the US. The current study aimed to develop validated prognostic nomograms to predict OS and CSS of patients with chordoma.
Materials and Methods
Patient eligibility and variables
The patient information was collected from the SEER database. The SEER*Stat software (Version 8.3.5; NCI, Bethesda, USA) was applied to the patient information acquired from the SEER database.
The inclusion criteria in the present study were as follows:
(2) Positive histological confirmation of chordoma;
(3) site limited to the skull base, vertebral column, and pelvis;
(4) confirmation of histologic type of chordoma;
(5) known cause of death and survival months after diagnosis.
The exclusion criteria in the present study were as follows:
(1) unknown use of radiotherapy, chemotherapy or surgery;
(2) unknown surgical stage;
(3) unknown tumor size
The clinicopathological features including patient age, gender, histology, surgical stage, tumor size, use of surgery, use of radiation, use of chemotherapy, and survival time were incorporated in the present study. The cutoff value of tumor size and age at diagnosis were calculated via X-tile software (Yale University, New Haven, Connecticut, USA). X-tile software was initially developed to determine the best cutoff values for variables in breast malignancy . The optimal cutoff values of chordoma tumor size in the current study were identified as 2.9 and 10.0 cm (Figure 1). The optimal age cutoff values of patients with chordoma were 38.54 and 66 years. The surgical stage in patients with chordoma was further categorized as localized, regional, and distant according to the American Joint Committee on Cancer (AJCC) staging system for bone sarcomas. Tumors confined to the periosteum were defined as localized tumors. And, a tumor that extended beyond the periosteum but without distant metastasis was defined as a regional tumor. Surgical resection was assigned to those who underwent surgical resection. However, the type of surgical resection such
as wide, marginal, and intralesional resection could not be obtained from the SEER