CHICAGO—Targeted drugs are very effective in patients with a well-specified molecular target. Examples include imatinib in patients with chronic myelog enous leukemia and trastuzumab in HER2-positive breast cancer. Evidence, however, has shown only modest improvements in outcomes when targeted agents are given to “unselected patients,” that is, those lacking a tumor characteristic (or mutation) that is specifically addressed by a given drug. “Little data exist regarding the true impact of targeted therapy in routine clinical practice,” said Janakiraman Subramanian, MD, of Washington University School of Medicine, St. Louis, Missouri, at the annual meeting of the American Society of Clinical Oncology. “Intolerable side effects are infrequent with targeted drugs, and discontinuation is primarily due to progressive disease,” he noted. “Iden tifying the proportion of patients who are ‘minimum users,’ defined as those who failed to refill their prescription more than once, would be one way of assessing treatment efficacy in routine practice.” Subramanian and his colleagues used studied claims in the Express Scripts pharmacy claims database from 2007 to 2009 for imatinib, lapatinib, erlotinib, sorafenib, sunitinib, and everolimus. Each patient’s age, sex, and duration of prescription were identified; the database does not include information on diagnosis and outcomes. Prescription claims for 14,300 pa tients were examined; most prescriptions were for erlotinib (43%), followed by imatinib (28%). A surprising proportion of patients did not refill their prescription after 60 days, including approximately 10% for imatinib, 21% for lapatinib, 31% for erlotinib, 38% for sorafenib, 44% for sunitinib, and 56% for everolimus. The proportion of prescription claims that were not filled past 60 days significantly differed between drugs prescribed to biomarker-selected patients (ie, imatinib and lapatinib) and drugs prescribed for nontargeted (unselected) patients (ie, erlotinib, sunitinib, sorafenib, and everolimus). Among the biomarker-selected patients, only 12% failed to refill prescriptions compared with 34% of the unselected patients (P <.001). “Targeted therapy for cancer in un selected patients leads to very high rates of early discontinuation,” Subramanian observed. In light of the frequent treatment discontinuation among unselected patients, the cost of the initial prescriptions (claims ≤60 days) may appear unjustifiably high in these drugs, resulting in the following rates: $2,695,945 for imatinib; $1,534,059 for lapatinib; $12,878,656 for erlotinib; $4,937,772 for sorafenib; $9,280,050 for sunitinib; and $218,916 for everolimus.