When you visit a doctor with symptoms, you expect answers. But getting the right diagnosis isn’t as straightforward as it should be.

Over 20 million American adults are misdiagnosed every year in outpatient settings. That’s roughly 2 in 10 patients walking out with the wrong answer or no answer at all.

Cancer sits at the top of the list for diagnoses that cause the most harm when missed.

Cancer Leads the Pack

Researchers at Johns Hopkins studied which missed diagnoses hurt patients most. They found that misdiagnosed cancers caused nearly 38% of deaths and serious permanent disabilities from diagnostic errors. That’s more than any other category, including strokes and infections.

Overall, cancer is misdiagnosed over 11% of the time. More than 6% of patients suffer serious harm from these mistakes.

Different cancers have different error rates. Lung cancer is missed about 22% of the time. Melanoma is missed nearly 14% of the time. Colorectal cancer is missed about 10% of the time. Breast cancer is missed about 9% of the time.

These aren’t rare diseases. They’re among the most common cancers, with well-known warning signs.

Why Doctors Miss Cancer

Most missed cancer diagnoses come down to a few repeating problems.

In primary care, over three-quarters of missed cancers involved errors in clinical judgment. Doctors failed to collect a full history or order a diagnostic test more than half the time. They failed to send patients to a specialist more than a third of the time.

Sometimes symptoms look like something less serious. Lung cancer often gets interpreted as asthma, COPD, or pneumonia. A persistent cough could be many things. Without the right tests, cancer hides in plain sight.

Ovarian and cervical cancers are most treatable in early stages when patients have no symptoms. When symptoms do appear, they often mimic less serious conditions like indigestion, urinary tract infections, or even pregnancy.

Colon cancer may be misdiagnosed as irritable bowel syndrome or hemorrhoids. These are common problems that doctors see every day. Cancer is not the first thing that comes to mind.

The Lung Cancer Problem

Lung cancer deserves special attention because it’s both commonly missed and commonly deadly.

For the record, I’m currently a co-investigator on a United Kingdom study funded by their National Health Service (NHS) in partnership with Imperial College London to improve early lung cancer and pancreatic cancer detection. 

At over 22%, lung cancer has one of the highest misdiagnosis rates. Nearly 14% of lung cancer patients experienced some harm from a doctor’s mistaken diagnosis.

Part of the problem is timing. Lung cancer may not be diagnosed quickly because patients don’t notice symptoms until more advanced stages. By the time someone feels sick enough to see a doctor, the cancer has often spread.

Another issue is assumptions. A doctor might not order lung cancer tests on someone who has never smoked, even though nonsmokers get lung cancer, too.

Breast Cancer: Missed in Plain Sight

Breast cancer is one of the most screened cancers in America. Yet mistakes still happen.

Mammograms can give false negative results, missing nearly 12% of breast cancers.

Young women and those with dense breast tissue face higher risks of missed diagnoses. A lump might be dismissed as a harmless cyst without further testing. Only a mammogram and a biopsy will help doctors rule out breast cancer if a woman has symptoms.

Who Gets Missed Most

Diagnostic errors don’t affect everyone equally.

Being a woman or a person of color increases the chances of misdiagnosis by 20% to 30%.

Only about 5% of images in general medical textbooks feature patients with dark skin. This means doctors get less training in recognizing how diseases appear on darker skin.

The result? Black patients with melanoma are about three times as likely as white patients to die within five years. Their cancers get caught later because the early signs were missed.

The Testing Breakdown

You might think ordering more tests would solve the problem. But tests create their own errors.

Nearly 70% of diagnostic errors occurred during the testing process. This includes ordering tests, collecting samples, processing results, and communicating findings.

More than 23% of testing errors came from technical problems like misused equipment or poorly processed samples. Another 20% came from mixed-up samples, mislabeled specimens, or tests performed on the wrong patient.

A test is only useful if it gets ordered, processed correctly, and reviewed by someone who acts on the results.

What Can Be Done

The good news? We know how to fix this. Heart attacks prove it.

The misdiagnosis rate for heart attacks is just 1.5%. That didn’t happen by accident. It took decades of focused efforts, research funding, and systems designed specifically around not missing heart attacks.

Diseases that receive the most attention to diagnosis have the lowest harm rates. Cancer hasn’t received that same focused effort on diagnosis. But reducing diagnostic errors by 50% for just five conditions, including lung cance,r could prevent up to 150,000 serious harms per year.

What You Can Do

Patients can take steps to protect themselves:

Know your family history. Many cancers run in families. Make sure every doctor knows if your relatives had cancer.

Don’t ignore symptoms that persist. A cough that won’t go away, unexplained weight loss, or changes in bathroom habits deserve investigation.

Ask about screening tests. Mammograms, colonoscopies, and other screenings catch cancers early when they’re most treatable.

Get a second opinion. If something feels wrong or a diagnosis doesn’t make sense, another doctor’s perspective can be valuable.

Be specific about your symptoms. When they started, what makes them better or worse, and how they’ve changed over time all help doctors narrow down possibilities.

The Bottom Line

Cancer misdiagnosis remains stubbornly common. Missed cancer diagnoses represent nearly half of all primary care diagnostic errors.

The conditions being missed aren’t mysterious. Lung, breast, colon, and prostate cancers are among the most studied diseases in medicine. The symptoms are documented. The screening tests exist.

What’s missing is a healthcare system designed around not missing them.

Until that changes, patients need to be their own advocates. Ask questions. Push for tests when symptoms don’t resolve. Get second opinions. Your persistence might save your life.

Consider Medome, www.medome.ai, to improve the prevention and earlier detection of cancer.