Factors Associated with Adherence Rates for Oral and Intravenous Anticancer Therapy in Commercially Insured Patients with Metastatic Colon Cancer

BACKGROUND: Over the past decade, oncology therapies have trended toward orally administered regimens, and there has been growing attention on evaluation of factors that affect adherence. There has not been a rigorous investigation of factors associated with adherence to intravenous (IV) and oral anticancer drugs in the setting of metastatic colorectal cancer (mCRC). OBJECTIVES: To (a) assess potential patient-specific factors related to adherence to mCRC chemotherapy regimens and (b) compare adherence with IV versus oral dosage forms. METHODS: A retrospective analysis was performed using the Optum Oncology Management claims database. Patients aged 18 years and older diagnosed with mCRC between July 1, 2004, and December 31, 2010, who were insured by a commercial health plan were included in the study. Adherence to IV and oral chemotherapy regimens was assessed using the National Comprehensive Cancer Network (NCCN) guidelines as the standard for expected cycle/regimen duration. The most commonly prescribed chemotherapy regimens were assessed. Adherence was evaluated using the medication possession ratio (MPR), calculated as the number of days a patient was covered by their chemotherapy regimen, according to NCCN guidelines, divided by the number of days elapsed from the first to the last infusion of that regimen. For most analyses, the MPR was considered a continuous variable that could take on values between 0 and 1. In other analyses, a dichotomous categorical variable designated if the MPR was at least 0.8 versus less than 0.8. The Wilcoxon rank sum, Kruskal-Wallis, and Student’s t-test were used to detect differences in continuous measures between patients receiving oral capecitabine therapy versus IV chemotherapy. The chi square test (X(2) test) or Fisher’s exact test was used to assess differences in the dichotomous MPR variable. Generalized estimating equation (GEE) models were used for regimen-level analyses to account for correlated responses within individuals. RESULTS: A total of 6,780 patients were included in the analysis, virtually all (98%) with commercial insurance coverage and the remaining (2%) with Medicare Advantage. Patients with mCRC received 17,095 regimens of chemotherapy, including 2,252 regimens of oral capecitabine. Of the 17,095 regimens, 6,780 (40%) were first-line regimens (i.e., the first time mCRC was treated for a given patient). The most common chemotherapy regimen, regardless of line of therapy, was FOLFOX (2,991 regimens, 17.5% of all regimens used). FOLFOX-based therapies with or without bevacizumab were the most common regimens for first- and second-line chemotherapy, while oral capecitabine treatment was the most commonly prescribed regimen for patients in third- or fourth-line therapy. Overall, medication adherence across all regimens was relatively high, with a mean MPR of 0.87 (SD = 0.17). Evaluation of the distribution of IV and oral capecitabine regimens revealed that 28% of all regimens were associated with an MPR of less than 0.8. The average MPR was clinically similar, but statistically higher for IV chemotherapy regimens (0.881) compared with oral capecitabine regimens (0.799; P < 0.0001). In the multivariable GEE model, lung or liver metastases were associated with a higher MPR, while lower Charlson Comorbidity Index and oral anticancer therapy were associated with lower MPR. Furthermore, as line of therapy increased, the difference in MPR between patients receiving oral capecitabine and IV chemotherapy increased. CONCLUSIONS: This analysis determined that adherence with IV chemotherapy regimens was clinically similar, but statistically higher, compared to oral capecitabine therapy. The difference in adherence rates between the 2 routes of administration increased as the line of anticancer regimen increased. These results suggest that there should be an increased focus on improving adherence rates in patients receiving oral capecitabine.