Cancer testing mistakes lead to patients missing out on treatment
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.
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.
Treatment for breast cancer depends on its particular subtype.
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.
'Inadvisable to rule out potential benefit from HER2-targeted therapy'
The researchers hypothesize that the difference in test results could be due to how the tests are carried out. At smaller pathology laboratories, the staff may be more inclined to use one of the two approved testing methods rather than both. They found that 18 of the 22 samples that were categorized incorrectly had been processed at a local laboratory using only one testing method.
There are certain limitations within the study, and the team admits that the 22 patients with centrally determined HER2 positive tumors was a relatively small number. They are also unaware of precisely how the initial testing was carried out in the local laboratories and whether there were any unidentified variables there.
Finally, they also admit that there are inherent limitations with tissue testing, such as tumor heterogeneity.
The researchers conclude their study by noting that it highlights the limitations of employing just one HER2 testing methodology and that it is inadvisable to rule out potential benefit from HER2-targeted therapy on the basis of a single test.
Recently, Medical News Today reported on two studies that suggested skin moles could be a predictor of breast cancer.
Written by James McIntosh
Copyright: Medical News Today
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