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Prognostic index for patients with parotid carcinoma: international external validation in a Belgian-German database
Vincent Vander Poorten1, Augustinus Hart, Tom Vauterin
1Department of Otorhinolaryngology, Head and Neck Surgery, University Hospitals, Leuven, Belgium. vincent.vanderpoorten@uzleuven.be
Background:
Prognostic indices for recurrence-free interval in patients with parotid carcinoma were developed and validated in a nationwide database. International validation would increase generalizability.
Methods:
In a Belgian-German database that contained 237 consecutive patients with parotid carcinoma, a pretreatment prognostic index (PS1) and a post-treatment prognostic index (PS2) were validated by calculating both indices for each patient, comparing coefficients, constructing survival curves, calculating the concordance measure C, and performing Wald tests for scale and weight optimization of included variables and for the possible inclusion of new variables.
Results:
Sixty-nine percent of patients (standard error, 5%) were disease free at 5 years. The defined cutoff points for PS1 resulted in 5-year disease-free rates from 94% (PS1 = 1) to 42% (PS1 = 4), and the cutoff points for PS2 resulted in 5-year disease-free rates from 93% (PS2 = 1) to 40% (PS2 = 4). Concordance measure C was good with 0.74 for both PS1 and PS2. Neither index could be improved statistically using this international database. There was some evidence that additional inclusion of the variable 'number of positive lymph nodes in the neck dissection specimen' could enhance the prognostic power of PS2.
Conclusions:
The prognostic indices performed adequately in this validation sample. Prospective generalized use seems to be well supported.