Although precision treatment strategies have been achieved with cancers such as chronic myeloid leukemia, which develop and can be targeted through a single driver event, most cancers are extremely heterogeneous and result from complex genetic changes.

Thus, newer, targeted therapies often have limited efficacy in broader patient populations, or the duration of response is short, as drug resistant subclones are selected for and eventually cause disease recurrence. Future cancer drug development is therefore dependent on being able to identify responding and non-responding patients, and effectively monitor and change treatment as the patient’s disease evolves.