The process of diagnosing cancer can be tricky, and when it goes wrong, it could impact patients, a new study shows.

The report, published in Cancer, examines cancer diagnosis data from four unnamed U.S. institutions.

The vast majority of cancer diagnoses had no errors. However, some errors in cancer diagnosis did show up, and experts had different opinions about how those errors might have affected patients.

The researchers included Stephen Raab, MD. He works in the pathology department of the University of Pittsburgh’s medical school.

Diagnostic Errors

The frequency of cancer diagnosis errors varied between the institutions, Raab’s team notes.

Errors were rare across the board. For gynecological cases, error frequency ranged from less than 2 percent to about 9 percent. For nongynecological cases, the range was nearly 5 percent to 12 percent, the researchers write.

All four institutions showed a “relatively high number” of nongynecological errors from specimens taken from the urinary tract and lung, the researchers note.

The Big Picture

The researchers estimated how common diagnostic errors might be in the U.S., assuming similar figures nationwide.

Take the Pap test, for example. The Pap test can screen for cancerous or precancerous abnormalities of the cervix, which is part of women’s reproductive system. If 50 million U.S. women get Pap tests in a year, at least 150,000 of them would have a diagnostic error in their test’s results, write the researchers.

Or, let’s say 5 million people got a nongynecological test, such as one from the lung or skin. The researchers estimate that at least 155,000 of them would have a diagnostic error in their test results.

What’s the Problem?

The researchers looked at two steps in cancer diagnosis: collecting tissue (such as from a biopsy) and analyzing it.

Most cancer diagnosis errors stemmed from the tissue collection process. Between 5 percent and 51 percent were due to misinterpretation, and experts didn’t always agree on the error’s source, the researchers write.

Harmful or Not?

How did the errors affect the patients? Did they lead to unnecessary tests, surgeries, or delays in diagnosis?

“Harm” was the term the researchers used for any consequence to a patient, whether it was mild (such as an extra blood test), moderate (such as an additional colonoscopy), or severe (including lengthy illness, loss of a body part, or death).

‘Harm’ to Patients

Many errors caused no “harm.” The rest mainly resulted in mild to moderate “harm,” the study shows.

“Harm” was noted in 45 percent of gynecological errors and 39 percent of nongynecological errors.

Remember, that’s a fraction of the few people who had cancer diagnosis errors and that “harm” didn’t necessarily mean dire consequences. Some gynecological cases of “harm” might have been as simple as a follow-up Pap test.

“We found that pathologists disagreed on the extent of harm caused by diagnostic errors,” they write. “Some institutions claimed that harm never occurred after an error in cancer diagnosis.”

Improving the Process

“The effect of diagnostic cancer errors on patient outcome is largely unknown,” write the researchers. “Clinicians often do not know when a diagnostic error has occurred and pathologists often have no knowledge of the effect.”

They recommend standardizing the reporting of cancer diagnosis errors. That would be a “first step in improving safety,” write Raab and colleagues.

By Miranda Hitti, reviewed by Louise Chang, MD

SOURCES: Raab, S. Cancer, Nov. 15, 2005; vol 104. News release, John Wiley & Sons, Inc.