The all-cash transaction gives owners of San Diego, California-based Ignyta $27.00 per share, a 74 percent premium to its closing price on the Nasdaq on Thursday.
Ignyta has focused on patients with cancers harbouring specific rare mutations, and currently has a treatment against certain tumours in a phase II trial that Roche said interim data showed to be promising.
Phase II trials of up to several hundred patients are designed to test the effectiveness of drugs and medical devices, and if successful are followed up by phase III trials on a larger number of patients before possible approval by regulators for use by patients.
"Cancer is a highly complex disease and many patients suffer from mutations which are difficult to detect and treat," Roche Pharmaceuticals' chief executive Daniel O'Day said in a statement.
"The agreement with Ignyta builds on Roche's strategy of fitting treatments to patients and will allow Roche to broaden and strengthen its oncology portfolio globally."
Roche has been seeking to expand its product portfolio as several of its most lucrative treatments are going off patent which opens them up to competition from cheaper generics.
Ignyta will remain based in San Diego.