USPSTF Transparency and Accountability Act of 2017 This bill amends the Public Health Service Act to expand the scope and responsibilities of the United States Preventive Services Task Force to require it to: (1) publish research plans to guide its review of scientific evidence relating to the effectiveness of preventive services; (2) make evidence reports and recommendations available for public comment; (3) establish a system for grading preventive care (Grades A, B, C, and D and a Grade I for insufficient information); and (4) convene a preventive services stakeholders board to provide feedback on task force activities and recommend preventive services and scientific evidence for the task force to review. Members of the task force and the preventive services stakeholders board must disclose conflicts of interest. The Government Accountability Office must report on: (1) current recommendations of the task force; (2) task force recommendations and recommendations of other federal health agencies, national medical professional societies, and patient and disease advocacy organizations; and (3) the impact of task force recommendations on insurance coverage, access, and outcomes, including the impact on morbidity and mortality. This bill amends title XVIII (Medicare) of the Social Security Act to revise HHS's authority to modify coverage of preventive services. HHS may modify such coverage only based on a task force grade or recommendation that was developed or updated in accordance with this bill. Medicare quality measures related to a recommendation of the task force may only be applied if the recommendation was developed or updated in accordance with this bill.