Can Cancer Be Misdiagnosed? | When to Get a Second Opinion

Yes, cancer can be misdiagnosed when it is missed entirely, when a benign condition is mistakenly called cancer.

A cancer diagnosis sounds absolute — either the cells are malignant or they aren’t. But the path from biopsy to final report passes through human interpretation, machine limits, and biological ambiguity. That’s where errors can creep in.

Research shows misdiagnosis takes several forms: a tumor that’s simply not seen on a scan, an indolent cancer that may never need treatment but gets labeled dangerous, or the right cancer with the wrong stage. Understanding these categories helps explain how they happen.

How Cancer Misdiagnosis Actually Happens

Cancer misdiagnosis isn’t one single problem. It covers three distinct scenarios: a false negative where cancer is present but missed, a false positive where benign tissue is read as cancer — also called overdiagnosis — and staging errors where the correct cancer type is found but the wrong stage or grade is assigned.

Overdiagnosis is the trickiest category. It happens when screening detects a cancer that would never have caused symptoms during a person’s lifetime. These indolent cancers sit in a grey zone — biologically malignant but clinically irrelevant for that patient.

In radiology, the most frequent cause of a missed tumor is a perceptual error. The tumor is visible on the image, but the radiologist simply doesn’t see it. It’s a human factor, not a technology failure.

Why the Most Common Cancers Are Also the Most Missed

The cancers we screen for most aggressively are the ones where diagnostic errors pile up. High volume creates more opportunities for mistakes, and some cancer types are simply harder to read than others.

• Breast cancer: A 10-year analysis of oncologic radiology errors found breast cancer is the single most commonly missed or improperly diagnosed entity. Mammography is the imaging modality most frequently involved in diagnostic errors.
• Colorectal cancer: Screening colonoscopy misses roughly 17 percent of colorectal cancers overall. For patients with a history of polyps, that miss rate jumps to about 33 percent.
• Lung, prostate, and bladder cancers: These round out the list of frequently misdiagnosed cancers, often due to overlapping features with benign conditions or limited biopsy samples.
• Gallbladder cancer: This one is often unexpected. It can be discovered incidentally during gallbladder removal, and some clinicians may not be looking for it, raising the risk of delayed diagnosis.

These aren’t rare edge cases. They represent known weak points in the diagnostic chain that affect thousands of patients each year.

The Hidden Cost of Diagnostic Errors

A study published in the Journal of Clinical Oncology found that errors in cancer diagnosis are likely the most harmful and expensive type of diagnostic error in medicine. The cost isn’t just financial — it’s measured in delayed treatment, unnecessary procedures, and patient distress.

Researchers note these failures are often preventable. They stem from breakdowns like misread imaging, pathology errors, or overlooked lab results. A Cleveland Clinic case study describes one patient initially diagnosed with stage 4 cholangiocarcinoma whose diagnosis was corrected after a second opinion misdiagnosis review changed the clinical picture entirely.

Mayo Clinic researchers have also demonstrated the value of second opinions. They note that without adequate resources to handle undifferentiated diagnoses, a potential unintended consequence is misdiagnosis resulting in treatment for the wrong condition.

Each error type has different root causes, but they all share one thing in common — a second review by a specialist can often catch them before any harm is done.

What You Can Do to Lower the Risk

You can’t eliminate diagnostic error from the outside, but you can build safety nets into your own care. Here are four steps supported by the research.

1. Seek a second opinion on pathology. Especially for rare cancers or before starting aggressive treatment. A different pathologist may see something the first reader missed.
2. Request a second radiology read. Some hospitals offer automatic second reads; if yours doesn’t, ask whether a second radiologist can review your imaging and report.
3. Keep your own medical records. Don’t assume one hospital’s system talks perfectly to another’s. Having your own copies of imaging discs and pathology reports gives you more control over the process.
4. Ask about incidental findings. If a scan was done for one reason and something unexpected showed up, ask specifically what it means and whether it needs follow-up.

Patient advocacy isn’t about distrusting your doctor. It’s about recognizing that the diagnostic system is complex and that a fresh set of eyes is a well-documented safeguard.

The Colorectal Cancer Example: A Closer Look

Colorectal cancer offers some of the most concrete numbers on misdiagnosis. NCI data on the missed colorectal cancer rate shows that screening colonoscopy misses about 17.22 percent of colorectal cancers — roughly one in six.

The miss rate isn’t uniform across all patients. Those who have had colorectal polyps in the past have a missed diagnosis rate of 33.3 percent — nearly double the baseline. This suggests that polyp history should prompt extra vigilance during follow-up and screening intervals.

Bowel preparation quality and operator experience also play a role. A clean, well-visualized colon gives the best chance of catching small or flat lesions that might otherwise hide behind folds.

These numbers don’t mean colonoscopy is a bad test — it remains the gold standard. They simply illustrate that no diagnostic tool is perfect, and knowing the limits helps patients and doctors interpret results more carefully.

The Bottom Line

Cancer misdiagnosis is a recognized risk that spans everything from a radiologist missing a visible tumor to a pathology lab labeling an indolent cancer as aggressive. The most effective countermeasure supported by institutions like Mayo Clinic and Cleveland Clinic is the second opinion — a fresh review of pathology slides and imaging by a specialist center.

If your diagnosis involves a rare cancer, an unexpected finding, or a treatment plan that feels mismatched to your daily life, seeking a second opinion from an academic medical center or a specialist in your specific cancer type is a reasonable step supported by the data.