INTRODUCTION
THE POWER OF PRECISION HEALTH

Imagine yourself in the not-too-distant future. Routine genomic screening tests, available at the time of birth, have shown that you have genetic variants that place you at high risk for pancreatic cancer in your adult years. Because of this propensity, you have elected to participate in a regular program of non-invasive screening tests that are designed to provide early detection of any tumor development in your pancreas. Every six months you take a pill that will cause a pancreatic tumor (if one exists) to shed a novel synthetic biomarker that can be detected in the urine.

Several days after you take one of the early cancer detection pills, your home's "smart toilet" automatically detects the synthetic biomarker in your urine. A device that is part of the smart toilet sends an alert to you on your smart phone, and to your primary care physician, who has your consent to receive information about these screening tests. To ensure the signal from the smart toilet is not a false positive, the signal is monitored in your urine over several days.

You follow the physician's recommendation to undergo imaging studies with molecular tracers that will identify the location of the tumor and ensure the toilet device was correct. A pancreatic tumor is detected that measures 1 cubic millimeter and there is no evidence that it has spread to other sites. You are given targeted therapies, which activate your immune system and destroy the tumor while it is still at an early stage of development. You continue the plan of close surveillance and monitoring with an early cancer detection pill every six months.

As I will describe in the pages that follow, all the components of this scenario are within our grasp today. We are in the midst of a revolution in science and technology related to the mechanisms of disease and, of equal importance, to the determinants of health and well-being. The impact of these advances and their broad dissemination are going to have a profound effect on our ability not just to treat diseases but to prevent them from developing in the first place. And in those instances when diseases cannot be prevented, they will be diagnosed much earlier and therefore treated much more effectively.

The example above illustrates just how transformative the results of this revolution are going to be. With pancreatic cancer today, there are no good tools for early detection, which means it is typically diagnosed much later in the course of tumor progression. In 80-95 percent of diagnoses, the cancerous tumor is locally advanced or metastatic [1]. As a result, 74 percent of all people with pancreatic cancer die within one year of diagnosis [2]. In 2017, this cancer resulted in the deaths of more than 43,000 people in the United States [3].

This vignette is emblematic of what the future of medicine should look like-and what I think it will look like-soon. Because for the first time in history, the world is starting to see the possibility of a new kind of medicine and health care. Instead of a race to cure disease after the fact, we can win the race before it even begins by preventing disease before it strikes-and curing it decisively if it does.

This approach is what we in Stanford Medicine have labeled "Precision Health" because it helps individuals thrive based on all factors specific to them, from their genetics to their lifestyle choices to their environment. It is based on the powerful idea that health care should promote health and wellness as much as it defeats disease.

Simply stated, the goals of Precision Health are to predict, prevent, and cure, precisely. And in that order, because more accurate prediction of propensity for disease will lead to more specific approaches for prevention. Even in cases where disease cannot be prevented altogether, diagnosing diseases much earlier in their course will mean that our ability to achieve cures will be greater than now. All too often today we identify diseases much too late to have the type of treatment outcome all of us would like to achieve.

THE PRECISION HEALTH PAST-AND PRESENT

The principles underpinning Precision Health reach back many years. The authors of a paper presented at a meeting of the American Public Health Association in 1873 wrote that "the custom of society must be changed so that the physician is employed to prevent rather than to cure diseases" [4]. Twenty years later, William Osler-often thought of as the originator of modern medicine-helped to found the medical school at Johns Hopkins University. And he was clear about the need for patient-centered medicine. "The good physician," said Osler, "treats the disease; the great physician treats the patient who has the disease." As a staunch advocate of prevention, Osler was well ahead of his time. He believed in both the power of scientific evidence and the power of bedside medicine. Precision Health is Osler's heir-the modern incarnation of his dual focus on rigorous science and the enduring physician-patient bond.

A focus on prevention was also at the heart of groundbreaking research that began in 1948. That year marked the launch of the Framingham Heart Study, which was an in-depth exploration of cardiovascular disease. At the time, the disease affected one of every three men in the United States, and it was twice as common as cancer [5]. Yet its cause was unknown. To better understand cardiovascular disease, an arm of the National Institutes of Health recruited more than 5,200 volunteers, between the ages of 30 and 59, in the Massachusetts town of Framingham to participate in a study. Each of the volunteers would be examined every two years, for a period of 20 years.

It became the most comprehensive such study ever undertaken and it continues today, with its third generation of participants. The discoveries it has brought forth have greatly expanded our understanding of the causes of cardiovascular disease and how to prevent it, through diet, exercise, and avoiding tobacco. Data from the study is the foundation of several risk prediction calculators for heart conditions, along with diabetes, fatty liver disease, and hypertension [6].

The knowledge unlocked by the Framingham Heart Study is a reminder of why researchers need to continue exploring the causes of different diseases-and to focus on preventing those diseases. Looking into the future, Project Baseline, a contemporary sequel to the Framingham study, holds the promise of dramatically increasing our understanding of health and disease by analyzing an enormously greater number of parameters. Like the Framingham study, Project Baseline, which I describe in more detail in the conclusion, is a longitudinal cohort study. One of its goals is tracking these parameters, and the health of the study volunteers, for a period of years.

KEY PRINCIPLES OF PRECISION HEALTH

There are many different dimensions of Precision Health, which I will elaborate on in this chapter and throughout the book. But some of the key features include the following:

Predictive and Preventive

Precision Health draws on the enablers of precision medicine-genomics, big data science, and regenerative medicine-but applies them in a predictive and proactive way. While precision medicine implies that individuals who get sick are treated precisely, Precision Health is focused on a holistic approach to keeping people healthy through targeted interventions and stopping disease before it starts. It seeks to understand the features of disease that explain why some people get sick when others do not, and which treatments, tests, and lifestyle changes will help prevent disease in each individual. When it isn't possible to altogether prevent a disease, Precision Health seeks to improve diagnostics such that diseases are detected much earlier and treated more effectively.

Personalized and Precise

With Precision Health, all forms of health and medical care are tailored to individual variations. That means doctors are able to provide every therapy based on what's known about a patient: their genetics, their metabolomics, all their -omics, their imaging, everything about them. As my colleague Thomas Robinson says, Precision Health is about identifying the right interventions, for the right person, at the right place, at the right time, in the right sequence. And information technology is deployed so that health professionals can confidently tell their patients, "You are going to benefit most from doing the following."

Patient-Centered

Health care today is often a complex and confusing journey, characterized by fragmentation and care on a disease-by-disease basis. Precision Health makes providers own the complexity of care for their patients, providing care that is seamless, coordinated around their needs, and based on the best science.

Participatory

Precision Health is focused on empowering individuals to monitor their own health. It breaks with the long-standing practice of people interacting with the medical system sporadically (the annual "check-up")-or when driven by illness or disease. Patients and their families get involved in the care delivery experience through practices such as continuous monitoring (as in the example provided in the scenario...