Not only is breast cancer more than one disease, but a single breast cancer tumor can also differ depending on where you look.
This means that tumor-sampling techniques used with “personalized medicine” gene expression profile tests may need refining to be sure that the most appropriate tumor sections are selected for testing.
“These tests are a good thing—they’ve done an incredible job identifying women with breast cancers that have a low risk of recurrence who don’t need chemotherapy, saving them from the toxicity and discomfort of unnecessary treatment,” says Adrian V. Lee, professor of pharmacology and chemical biology at the University of Pittsburgh Cancer Institute.
“However, as with any new technology, we need to understand how these tests work, and we’re finding that the sampling process, which involves liquefying tumors, loses information that could be important in determining the best treatment plan for patients with more aggressive tumors.”
Gene expression profiling is an increasingly popular type of test that tells doctors what certain genes are doing in a tissue sample, such as causing the cells to actively divide and multiply. Several tests have been developed in recent years to aid oncologists in developing breast cancer treatment plans. They involve taking a small bit of the tumor—or multiple small bits mixed together—and testing it.
The tests can tell oncologists if the cancer has a low, intermediate, or high risk of recurring. The level of risk can help doctors and patients decide whether an aggressive treatment plan involving chemotherapy is beneficial or likely to do more harm than good.
For the study, published in Clinical Cancer Research, researchers examined 71 cases of a type of breast cancer called “estrogen-receptor-positive” that was caught early and hadn’t yet spread to other parts of the body. In all cases, the tumor had been removed and samples taken for gene expression profiling.
A total of 181 samples were taken from various parts of the tumors. Researchers measured the expression of 141 different genes from five different types of gene expression profile tests commonly used for breast cancer tumors.
The tumors of 25 percent of the patients received a different risk of recurrence score depending on which sample was processed.
“This indicates that one part of the tumor is more aggressive than another part. If an oncologist were to know this, he or she would likely recommend a treatment plan tailored to destroy the most aggressive section of the tumor,” Lee says.
Because the patients in this study were all caught early, their risk of recurrence was low to begin with, and there weren’t enough recurrences to make a meaningful determination on whether they would have done better if more samples were tested from their tumors.
“It would be valuable to repeat this study with a much larger group of breast cancer patients and follow them over time so that we could definitively determine if the way sampling is done with these tests is, indeed, resulting in patients getting cancer recurrences that wouldn’t have happened if the sampling process was changed,” Lee says.
The Breast Cancer Research Foundation, the National Cancer Institute, Fashion Footwear of New York, and UPMC supported the work.
Source: University of Pittsburgh