In his final State of the Union address one year ago, President Obama announced a “moonshot” initiative to “cure cancer once and for all.”

Though the moonshot will be one of Obama’s few health programs to continue under President Donald Trump — its $1.8 billion budget is secure — today, on World Cancer Day, it remains more difficult than ever to imagine a real cure.

Take the 50-year-old man diagnosed with prostate cancer in my clinic at Brigham and Women's Hospital in Boston. He received a novel procedure to remove his prostate, and later received focused radiation to try to eradicate any remaining cancer. Unfortunately, his disease returned a year later. But after two new therapies, his cancer now appears in check. And if his cancer does spread, a host of other treatments — including many not even on the market yet — may put his cancer back in remission.

As with most cancers after treatment, my patient’s disease is under control, but not cured. And it likely will never be.

The problem with the “moonshot” idea is that it focuses on magic bullets, at the expense of the majority of current and future cancer patients. To eliminate the global burden of cancer, patients and doctors need an equal focus on prevention as on cure — or we need to redefine the word “cure” altogether. With increased funding for prevention research and wider dissemination of prevention initiatives, we could be even closer to eradicating cancer entirely.

The biggest lesson from the war on cancer is that we are incredibly far from a cure

Why do we think that we can cure cancer? In his book The Death of Cancer, former National Cancer Institute director Vincent DeVita writes that the United States' war on cancer came about in the 1970s due to an assortment of advocates and politicians. Their mission was articulated best by the National Panel of Consultants on the Conquest of Cancer, whose report in 1970 called for “the conquest of cancer.”

At the time, the concept of “cure” was eradication of cancers after they were diagnosed — to treat cancer with chemotherapy just as we treat infectious diseases with antibiotics. And so millions of dollars went toward funding research that studied and created novel therapies for cancer. And the idea of a “war on cancer” has persisted, with the “moonshot” its most ambitious attack yet.

The war on cancer has succeeded in creating more treatments, and oncologists have moved from extremely toxic chemotherapies to targeted molecular therapies, such as the drug imatinib for chronic myelogenous leukemia, which control cancer in many more individuals. Now cancer therapy has been revolutionized by “immunotherapies” that ramp up the body’s own immune system to fight cancer.

But perhaps the biggest lesson from the war on cancer is that we are incredibly far from a cure. Cancer is not one disease but thousands, each with its own causes and genetic markers.

Take non–small cell lung cancer (NSCLC), the most common cause of cancer death in the US. According to National Cancer Institute data, more than half of people with lung cancer are diagnosed after cancer has spread beyond the lung; more than 80 percent of these patients die within a year. Research on molecular targets has suggested that there are more than 15 different “driver” mutations in NSCLC, and most tumors possess a multitude of these mutations.

Just as it is difficult to defeat an army of enemies by picking off individual soldiers one at a time, even one targeted therapy in metastatic NSCLC is unlikely to eradicate the entire disease. That’s the case with most cancers and may explain why 63 percent of oncologists would never tell a patient that they are cured after treatment. Even newer immunotherapies at best delay the progression of cancer, but cannot cure it. It remains difficult, if not impossible, to cure cancers — if we define cure as treatment.

New treatments open up an entirely new vision of preventative “cures”

Prevention may instead provide the solution we have long been seeking. The 23 percent reduction in the US cancer mortality rate over the past two decades — 1.7 million cancer deaths prevented — is due in large part to cancer prevention interventions. These include large-scale screening efforts in mammography and colonoscopy as well as increased vaccination efforts.

We can also find new innovations in prevention, some which may even eliminate incurable cancers. Hepatocellular carcinoma (HCC) is the third most common cause of cancer death in the world, and a major cause of morbidity globally. The hepatitis C virus is the major cause of HCC: Infected individuals have a 17-fold increased risk of developing HCC compared with non-infected individuals.

Until recently, hepatitis C was incurable, and treatment to control the disease was associated with significant side effects. But in 2013, the drug sofosbuvir (trade name Sovaldi) was approved and offered many patients the opportunity to permanently eliminate hepatitis C — and prevent the possibility of subsequent HCC.

Sofosbuvir, among other treatments, opens up an entirely new vision of “cure” in cancer, more proactive than our previous conceptions. The need for prevention is dire: Tobacco control, good nutrition, vaccinations, and physical activity could prevent almost half of all cancers. Unfortunately, rates of hepatitis and human papillomavirus vaccination have remained below 60 percent for a decade. By focusing our efforts on the upstream determinants of cancer, we can achieve the elimination of cancer that has eluded us for the past 50 years.

Unfortunately, there are no active moonshot grants funding prevention or early detection efforts. And the Blue Ribbon Panel Report, which describes the 10 research priorities for the moonshot, barely mentions prevention or early cancer detection. If this trend continues, funding for cancer prevention and control will be crowded out within the shrinking pie of federal research dollars.

Our cancer moonshot is a worthwhile goal — and will continue into Donald Trump’s presidency. More investment in eliminating cancer will accelerate progress. And developing new therapies is part of that strategy.

But we must acknowledge that a treatment that permanently eliminates cancer will likely never be found. Investing in creating and disseminating prevention strategies will save countless more lives than newer cancer treatments. This is the best chance of permanently eliminating cancer, nailing the cure that we all want.

Ravi Parikh is a resident in internal medicine at Brigham and Women's Hospital in Boston. Find him on Twitter @ravi_b_parikh.

Further reading on Vox:

Angelina Jolie’s breast cancer op-ed may have cost the health system $14 million in unnecessary tests

4 behaviors that may cut the risk of cancer by 30 percent

Cancer scientists are having trouble replicating groundbreaking research