Rationale: Although commonly used as the primary outcome measure of clinical trials in pulmonary arterial hypertension (PAH), the minimal important difference (MID) of the 6-minute walk test (6MWT) has not been well defined for this population of patients. Objectives: To estimate the MID in the 6MWT in patients with PAH. Methods: Study subjects from the clinical trial of tadalafil in PAH, a 16-week, parallel-group, randomized clinical trial of patients who were treatment naive or on background therapy with an endothelin receptor antagonist, were eligible. 6MWT was performed using a standardized protocol. Distributional and anchor-based methods were used to estimate the MID; the latter method used the Physical Component Summary Score (PCS) of the Medical Outcomes Study 36-item short form (SF-36). Measurements and Main Results: Four hundred five subjects were analyzed. Domains of the SF-36 were weakly to modestly associated with 6MWT. Change in the PCS of the SF-36 was most strongly associated with change in 6MWT (r ¼ 0.40, P , 0.001) and thus was selected as the anchor for subsequent anchor-based analyses. Distributional analyses yielded estimates of the MID ranging from 25.1 to 38.5 m, whereas anchor-based analyses yielded an estimate of 38.6 m. Conclusions: Using both distributional and anchor-based methods, the estimated consensus MID in the 6MWT for PAH is approximately 33 m. These results have important implications for (1) assessing treatment responses from clinical trials and metaanalyses of specific PAH therapy, and (2) sample size calculations for future study design.

Purpose:To investigate whether qualitative magnetic resonance (MR) imaging assessments of background parenchymal enhancement (BPE), amount of fibroglandular tissue (FGT), and mammographic density are associated with risk of developing breast cancer in women who are at high risk. Materials and Methods:In this institutional review board-approved HIPAA-compliant retrospective study, all screening breast MR images obtained from January 2006 to December 2011 in women aged 18 years or older and at high risk for but without a history of breast cancer were identified. Women in whom breast cancer was diagnosed after index MR imaging comprised the cancer cohort, and one-to-one matching (age and BRCA status) of each woman with breast cancer to a control subject was performed by using MR images obtained in women who did not develop breast cancer with follow-up time maximized. Amount of BPE, BPE pattern (peripheral vs central), amount of FGT at MR imaging, and mammographic density were assessed on index images. Imaging features were compared between cancer and control cohorts by using conditional logistic regression. Results:Twenty-three women at high risk (mean age, 47 years 6 10 [standard deviation]; six women had BRCA mutations) with no history of breast cancer underwent screening breast MR imaging; in these women, a diagnosis of breast cancer (invasive, n = 12; in situ, n = 11) was made during the follow-up interval. Women with mild, moderate, or marked BPE were nine times more likely to receive a diagnosis of breast cancer during the follow-up interval than were those with minimal BPE (P = .007; odds ratio = 9.0; 95% confidence interval: 1.1, 71.0). BPE pattern, MR imaging amount of FGT, and mammographic density were not significantly different between the cohorts (P = .5, P = .5, and P = .4, respectively). Conclusion:Greater BPE was associated with a higher probability of developing breast cancer in women at high risk for cancer and warrants further study.q RSNA, 2015

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