There have been a number of targeted sequencing experiments of breast cancer cells before: using next gen sequencing platforms and microarrays. Comlpete sequencing is by no means a breakthrough. A complete sequencing (3bn letters) has not been tried for a reason - and that reason is that the increase in information content from complete sequencing is minimal - almost zero. infact it will be wasteful exercise to look at the whole genome when you expect to find problem in a handful of genes. Moreover the full sequence of a tumor cell varies from patient to patient and also between cell to cell in the same patient (unlike in healthy cells/patients). that's why no one does full genome sequencing of tumor cells - just targeted sequencing of selected genes.