CAMBRIDGE — With personalized medicine becoming a key focus for medical research and diagnosing conditions, Partners HealthCare System, the region’s largest hospital and physicians network, is positioning itself to become a national leader in the emerging field.

Starting next month, Boston-based Partners will launch a “whole genome” sequencing and interpretation service for patients at its nine hospitals across Eastern Massachusetts, including Massachusetts General and Brigham and Women’s. The service, which will cost about $9,000, is intended to help doctors and patients make critical decisions about treatments — for example, which breast cancer drug could work best based on a patient’s genetic makeup.