GlaxoSmithKline ( GSK ) agreed to buy Tesaro ( TSRO ) for $5.1 billion, gaining a class of cancer drugs called PARP inhibitors that work by blocking an enzyme that cancer cells use to repair damage in their DNA, STAT writes. PARP inhibitors are believed to be active in ovarian and prostate cancers, and are being studied in combination with immunotherapy drugs. The deal is expected to allow the big drug maker to "develop wholly owned combination therapies in multiple tumor types," Glaxo chief executive Emma Walmsley says.