Increased or decreased? mtDNA mutations in cancerous cells

Just saw two recently published papers:

Liu et al. 2012. Deciphering the Signature of Selective Constraints on Cancerous Mitochondrial Genome. Molecular Biology and Evolution, 29 (4): 1255-1261.


Ericson et al. 2012. Decreased Mitochondrial DNA Mutagenesis in Human Colorectal Cancer. PLoS Genetics, 8(6): e1002689.


I wonder if mtDNA mutations are increased or decreased in cancer cells compared to their adjacent normal cells, as the two articles gave contradictory conclusions. Of course I should read through them thoroughly before saying anything new.