Mistakes in diagnosing cancer are common and often result in delays and additional costs that are harmful to patients.

In a study funded by the Agency for Healthcare Research and Quality, a government-mandated error detection method found up to 12 percent of reviewed specimens had an erroneous diagnosis.

Stephen S. Raab, MD, of the University of Pittsburgh School of Medicine and colleagues examined tissue specimens, pathologists' findings, and medical records from four institutions that diagnose precancerous and cancerous lesions in an effort to characterize the frequency, cause and impact of errors in cancer diagnosis.

Multiple Tests, Different Results

Patients often have multiple tests in order to diagnose cancer. The researchers reviewed cases when multiple tests produced different diagnoses for the same individual.

Errors were frequent and institution-dependent, they found.

Up to 9 percent of gynecologic specimen pairs (Pap test and cervical biopsy) were incorrect. Up to 12 percent of non-gynecologic specimen pairs contained an error.

Differences in institutional error rates most likely are related to bias in error reporting, the researchers suggest, although better methods may have resulted in fewer mistakes at some institutions.

Most of the errors were due to poor specimen collection. The proportion of errors attributed to pathologist misinterpretation ranged from 5-50 percent. Pathologists frequently disagreed with the assignment of error cause when reviewing specimens from other institutions.

Delayed Diagnoses

Gynecologic errors led to harm in 45 percent of cases, while non-gynecologic errors were harmful in 39 percent of cases, a review of medical records showed.

The most likely harm consists of diagnosis delays and costly additional testing. The researchers note that is very rare that unneeded procedures are performed for the false positive diagnosis of cancer.

Pathologists disagreed on the severity of harm resulting from an error in cancer diagnosis.

This study demonstrates a relatively high frequency of error, the researchers say. Also, variability in practice makes it difficult to understand what factors are causing the mistakes.

"The standardization and uniform reporting of errors in cancer diagnosis is a first step in improving safety," the authors conclude.