Kim et al, 2015 Cancer Cell
Link to abstract: http://www.cell.com/cancer-cell/abstract/S1535-6108(15)00265-2
Kim et al examined 38 pairs of primary and relapsed GBMs using CGH-array, whole exome sequencing, and RNA Seq. They found that distant relapses had a much more divergent mutation profile compared to local relapses. It has also been previously known that IDH1 mutant tumors (usually progressed from LGG) have a hypermutation profile at relapse if initially treated with temozolamide. Kim et al confirmed this finding but also found that it does not hold true for IDH1 wild type tumors.
*You can read an excellent summary of this paper in the same issue by Vijay Ramaswamy and Michael Taylor (see http://www.cell.com/cancer-cell/abstract/S1535-6108(15)00301-3).