Cancer testing mistakes lead to patients missing out on treatment

Breast cancer cells

A new study recently published in Cancer has found that the conventional way in which doctors classify breast cancer tumors has limitations, leading to incorrect results for cancer patients. This incorrect classification restricts the treatment that these patients go on to receive, researchers say.

Around 1 in 8 American women will develop invasive breast cancer at some point in their lives. In 2013, the following cases of breast cancer were expected to be diagnosed in the US:


  • 232,340 new cases of invasive breast cancer in women
  • 2,240 new cases of invasive breast cancer in men
  • 64,640 new cases of non-invasive in situ breast cancer
  • 39,620 women were expected to die from breast cancer.

In the US, breast cancer is the most commonly diagnosedcancer among women, and its death rates are higher for women than any other cancer, apart from lung cancer.

Diagnosis and classification

Breast cancer is categorized into different subtypes, so when doctors diagnose breast cancer, they try to classify it into one particular subtype. Researchers from the Dartmouth-Hitchcock Norris Cotton Cancer Center examined how accurately testing was able to classify cancers in one specific subtype, those that are human epidermal growth factor receptor 2 (HER2) positive.

The authors state that the accurate assessment of HER2 status is essential to determine optimal treatment options. If breast cancer is found to be HER2 positive, then there are particular treatments for preventing recurrence and improving outcome for this type of cancer that are extremely effective.

The researchers re-tested tumor samples from a group of 530 women to see if their initial HER2 negative classification had been correct.

When retesting the samples, the researchers utilized two different tests: immunohistochemistry (IHC) and florescence in situ hybridization (FISH). Both tests are approved by the US Food and Drug Administration (FDA) and used widely.

They found that 22 out of 530 patients had had their tumor type incorrectly classified – 4% of the total number.

Dr. Peter Kaufman discusses the implications of their study:

“We, and other groups, have previously shown that a certain percentage of cases found to be HER2 positive in local laboratories are in fact HER2 negative when tested in more experienced central labs. There has, however, been almost no research evaluating the accuracy of a negative HER2 result. This is the first large study to look at this. What is comforting is that we found that re-testing in experienced larger labs confirmed the original local lab results in the majority of cases.”

Dr. Kaufman acknowledges that the incorrect classification of 4% of patients is problematic, as therapies that specifically target HER2 are critically important for people with HER2 positive breast cancer. The 4% did not receive potentially efficacious therapy because their HER2 positivity was not determined to begin with.

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