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Table 3: Kaplan-Meier curves for survival using log-rank tests in patients with recurrent chordomas
Explanatory Variables Total No. No. of Events P Value
Univariate models 
    Age at first operation (yr) .312
        Younger than 60 10 5 
        60 or older 6 2 
No. of surgical resections at first MRI .002
    1 11 3 
    ≥2 5 4 
Tumor volume .957
    <3 × 10³ × mm³ 10 4 
    ≥3 × 10³ × mm³ 6 3 
Histopathology 
    Chondroid chordoma 5 1 .346
    Classic chordoma 11 6 
Tumor location .507
    Clivus 11 5 
    Other sites 5 (C = 1, L = 2, S = 1, other = 1) 2 
Adjuvant radiation therapy .172
    None/unknown 3 2 
    Done 13 5 
Mean ADC (for an aggressive tumor) .006
    >1.494 × 10⁻³ × mm²/s 10 2 
    ≤1.494 × 10⁻³ × mm²/s 6 5 
Note:—C indicates cervical spine; L, lumber spine; S, sacrum.

Explanatory Variables	Total No.	No. of Events	P Value
Univariate models
Age at first operation (yr)			.312
Younger than 60	10	5
60 or older	6	2
No. of surgical resections at first MRI			.002
1	11	3
≥2	5	4
Tumor volume			.957
<3 × 10³ × mm³	10	4
≥3 × 10³ × mm³	6	3
Histopathology
Chondroid chordoma	5	1	.346
Classic chordoma	11	6
Tumor location			.507
Clivus	11	5
Other sites	5 (C = 1, L = 2, S = 1, other = 1)	2
Adjuvant radiation therapy			.172
None/unknown	3	2
Done	13	5
Mean ADC (for an aggressive tumor)			.006
>1.494 × 10⁻³ × mm²/s	10	2
≤1.494 × 10⁻³ × mm²/s	6	5