title: Kernel based methods for accelerated failure time model with ultra-high dimensional data.
abstract: BACKGROUND
  Most genomic data have ultra-high dimensions with more than 10,000 genes (probes). Regularization methods with L₁ and L(p) penalty have been extensively studied in survival analysis with high-dimensional genomic data. However, when the sample size n << m (the number of genes), directly identifying a small subset of genes from ultra-high (m > 10, 000) dimensional data is time-consuming and not computationally efficient. In current microarray analysis, what people really do is select a couple of thousands (or hundreds) of genes using univariate analysis or statistical tests, and then apply the LASSO-type penalty to further reduce the number of disease associated genes. This two-step procedure may introduce bias and inaccuracy and lead us to miss biologically important genes.
  
  
  RESULTS
  The accelerated failure time (AFT) model is a linear regression model and a useful alternative to the Cox model for survival analysis. In this paper, we propose a nonlinear kernel based AFT model and an efficient variable selection method with adaptive kernel ridge regression. Our proposed variable selection method is based on the kernel matrix and dual problem with a much smaller n x n matrix. It is very efficient when the number of unknown variables (genes) is much larger than the number of samples. Moreover, the primal variables are explicitly updated and the sparsity in the solution is exploited.
  
  
  CONCLUSIONS
  Our proposed methods can simultaneously identify survival associated prognostic factors and predict survival outcomes with ultra-high dimensional genomic data. We have demonstrated the performance of our methods with both simulation and real data. The proposed method performs superbly with limited computational studies.
authors.affiliation: University of Maryland Greenebaum Cancer Center, 22 South Greene Street, Baltimore, MD 21201, USA. zliu@umm.edu
authors.forename: Zhenqiu
authors.initials: Z
authors.lastname: Liu
authors.forename: Dechang
authors.initials: D
authors.lastname: Chen
authors.forename: Ming
authors.initials: M
authors.lastname: Tan
authors.forename: Feng
authors.initials: F
authors.lastname: Jiang
authors.forename: Ronald B
authors.initials: RB
authors.lastname: Gartenhaus
mesh_terms: D000465:Algorithms; D020869:Gene Expression Profiling / Q000379:methods*; D016014:Linear Models; D020411:Oligonucleotide Array Sequence Analysis / Q000379:methods*; D016019:Survival Analysis