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7005 Background: Studies suggest that decreased microbial diversity due to chemotherapeutic and antibiotic exposure may be associated with acute graft vs host disease (aGvHD) and mortality in patients undergoing allogeneic HSCT. In addition, disruption of the microbiome by antibiotics may lead to intestinal domination by pro-inflammatory bacteria, resulting in increased risk of aGvHD. This relationship has been described in settings with prophylactic antibiotic use, a standard of care in most transplant centers. Here we assessed how the microbiome and GvHD outcomes differ when prophylactic use of antibiotics is avoided. Methods: We collaborated on an observational study (COLLECT) to evaluate changes in microbial diversity over time in subjects undergoing allogeneic HSCT. According to protocol at the University Hospital of Cologne, antibiotics were administered only as empiric treatment for febrile neutropenia or as targeted treatment. Stool was collected weekly from 65 subjects at baseline (pre-HSCT) to day 28 with additional time points taken at day 56, day 90, day 365, and upon diagnosis of intestinal GvHD (GvHD-day 0 and GvHD-day 7). Patients were monitored for incidence of GvHD, including acute GvHD of the liver, intestine, and skin. Microbiome 16SV4 profiles were generated from 381 stool samples. Linear effects models were developed to evaluate the association between Shannon diversity, intestinal domination, and the incidence of intestinal GvHD and mortality. Results: Of the 65 subjects, 28 subjects (42%) went on to develop intestinal GvHD, and 16 subjects (25%) did not survive to day 365. A decline in Shannon diversity was observed during the neutropenic period following HSCT. Subjects who went on to develop intestinal GvHD had significantly lower Shannon diversity at the time of stem cell engraftment (p < 0.0468). Furthermore, lower diversity was observed throughout the study period in subjects experiencing intestinal GvHD. We developed a linear model evaluating the association between mortality and Shannon diversity and found a significant relationship at days 28 and 90 post HSCT (p < 0.0001 and 0.0121, resp). Intestinal domination by Enterobacteriaceae or Enterococcus was significantly associated with the incidence of intestinal GvHD (p < 0.0082) or mortality (p < 0.001), respectively. Conclusions: Data from this observational study (COLLECT) suggests decreases in microbial diversity over time occur in subjects undergoing allogeneic HSCT despite the lack of prophylactic antibiotics. Investigation of whether administration of microbiome therapeutic drugs prior to transplant and/or at the time of engraftment can reduce morbidity and mortality in this high-risk patient population is warranted. Clinical trial information: NCT03148197.

12061 Background: Despite life-saving potential, many women struggle to adhere to adjuvant endocrine therapy (AET) for their early-stage, hormone receptor-positive breast cancer. Prior research has demonstrated that emotional distress is a barrier to AET adherence. The current study aimed to test the long-term effects of two 5-week post-surgical group-based stress management interventions, cognitive behavioral therapy (CBT) and relaxation training (RT), versus an attention-matched health education (HE) control on AET adherence at long-term follow-up. Methods: We conducted long-term follow-up (median = 8 years, range = 7-11 years) of a cohort of women who enrolled in a randomized controlled trial of CBT vs. RT vs. HE shortly after surgery for stage 0-3 breast cancer.We measuredadherence with the Endocrine Therapy Medication Usage Questionnaire (ETMUQ) given at long-term follow-up. First, we established adherence factors on the ETMUQ via confirmatory factor analysis. We then used structural equation modeling to regress these factors on study arm, controlling for patient age, stage of disease, and treatments received (chemotherapy/radiation). Results: The sample was predominately middle-aged ( M= 54.81, SD= 10.19), White (41.5%) and Hispanic (42.2%), partnered (62.2%) with stage 1 (57.0%) or stage 2 (25.9%) disease. Of the women who completed long-term follow-up (N = 59, 44.7% of original sample); more than half (n = 30; 50.8%) reported having at least some problems with adherence. There was an effect of intervention group on adherence, such that women receiving RT (n = 15) had significantly better adherence than those receiving CBT (n = 20) on the factor measuring Forgetfulness/Inconsistency ( B(SE) =.57 (.34), p=.001), and marginally better adherence than those receiving CBT on the factor measuring Intentional Nonadherence ( B(SE) =.60 (.33), p =.062). There was no such effect when comparing RT or CBT to HE (n = 24). Conclusions: Women receiving RT were less likely to forget to take their AET and marginally less likely to intentionally miss doses of AET in the long-term compared to women receiving CBT. Future research could investigate the mechanism by which RT may improve adherence. For example, RT may reduce somatic symptoms related to AET or improve a patients’ self-efficacy to cope with these symptoms thereby reducing intentional non-adherence. In addition, RT may improve patients’ attention and awareness leading to less forgetfulness. Clinical trial information: NCT02103387.