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Background: Adherence and persistence studies face several methodologic difficulties, including short-term mortality. We compared approaches to quantify adherence and persistence to first line (1L) oral targeted therapy (TT) in patients diagnosed with metastatic renal cell carcinoma (mRCC). Methods: Patients with mRCC ages 66 years or more who initiated TTs within 4 months of diagnosis were identified in the Surveillance, Epidemiology, and End Results Medicare-linked database (2007–2015). Adherence [proportion of days covered (PDC) >80%] was calculated using (i) PDC with a fixed 6-month denominator including then excluding patients who died within the 6 months and (ii) PDC with a denominator measuring time on treatment. Risk of nonpersistence was obtained by censoring death or treating death as a competing risk using cumulative incidence functions. Results: Among 485 patients with mRCC initiating a 1L oral TT (sunitinib, 64%; pazopanib, 25%; other, 11%), 40% died within 6 months. Adherence was higher after restricting to patients who survived (60%) compared with including those patients and assigning zero days covered after death (47%). Risk of nonpersistence was higher when censoring patients at death, 0.91 [95% confidence interval (CI), 0.88–0.94], compared with treating death as a competing risk, 0.75 (95% CI, 0.71–0.79). Conclusions: Different approaches to handling death resulted in different adherence and persistence estimates in the metastatic setting. Future studies should explicitly report the proportion of patient deaths over time and explore appropriate methods to account for death as competing risk. Impact: Use of several approaches can provide a more comprehensive picture of medication-taking behavior in the metastatic setting where death is a major competing risk.

Background: The pharmacy reference database, Micromedex, lists concomitant hydrochlorothiazide and cyclophosphamide use as a potential, major drug–drug interaction (DDI), although only one small, single-center study supports this claim. Our objective was to estimate associations between this potential DDI and two adverse chemotherapy-related events, neutropenia-related hospitalizations and treatment regimen discontinuation, among a cohort of women with breast cancer initiating adjuvant chemotherapy containing cyclophosphamide. Methods: Using linked Surveillance, Epidemiology, and End Results Program (SEER)-Medicare data, we included women 66 years and older with breast cancer diagnosis between 2007 and 2011, who initiated a regimen containing cyclophosphamide. Risk ratios (RR) and 95% confidence intervals for adverse outcomes comparing women exposed versus unexposed to the potential DDI were assessed using modified multivariable Poisson regression adjusting for potential confounders. Results: In total, 27% of women receiving cyclophosphamide treatment were exposed to concomitant hydrochlorothiazide, of which 11% experienced a neutropenia-related hospitalization and 21% discontinued their chemotherapy regimen prior to completion. Adjusted risks of both adverse events were similar between those exposed and unexposed to the potential DDI [neutropenia-related hospitalization: adjusted RR (aRR) = 0.92 (0.70–1.21); treatment discontinuation: aRR = 1.00 (0.96–1.05)]. Conclusions: Our results do not support an association between concomitant hydrochlorothiazide use and two clinically relevant adverse chemotherapy-related events. Impact: Our results support reassessing and potentially lowering severity of this potential interaction in drug reference databases.