New Gene Test Identifies Tumors of Unknown Origin

Between 3 percent and 15 percent of newly diagnosed cancers in the U.S. each year are classified as tumors of unknown origin or TUO, meaning simply that the type of cancer cannot be readily identified. At one time, when cancer treatment was general, this was not a problem. Today, however, most cancer treatments are selected specifically for the type of tumor. Giving the wrong treatment may slow the recovery of the patient or even have negative reactions. Equally important are cases of possible recurrence. Being able to identify a tumor as a recurrence or another primary is critical to treatment and patient outcomes. When the tumor type is unknown, selection of treatment is difficult or impossible which means the patient loses precious time.

Even while the need is critical, diagnosing tumors of unknown origin has been a complex, costly and inexact process. Assessing a TUO involves using multiple technologies including chemistry, hematology and immunoassay testing, immunohistochemistry, chest X-ray, tomography, mammography, ultrasound, colonoscopy, esophagogastroduodenoscopy and bronchoscopy. The cost to identify the primary site of the tumor has traditionally been between $4,600 and $17,900 per patient. Only 25 percent to 30 percent of all TUOs are successfully identified using these traditional methods.

At the recent San Antonio Breast Cancer Symposium, US LABS introduced a new testing methodology for identification of tumors of unknown origin. Currently available only for research applications, this new test uses a technology called Gene Expression Profiling, a type of genomics testing. The new method reduces the complex, multi-step diagnostics traditionally used to a single test that has exhibited 86 percent accuracy and the ability to generate calls in 91 percent of cases. Gene Expression Profiling is performed on the patient's tissue sample that is sent to the lab embedded in paraffin. This is the most common specimen source in use today. Consequently, patients aren't required to do extra tests or spend extra time. The cost of the test is $2,000.

Gene Expression Profiling is performed on a patient's RNA sample that is put through what is called laser capture microdissection. This process allows for an enriched sample of the tumor to be selected that actually increases the yield of RNA for analysis. A series of steps are performed on the RNA resulting in a gene expression. This expression is then compared by the US LABS system to over 60 different kinds of cancer, 24 tissue or organ sites and 69 tumor types accounting for more than 90 percent of all known cancers.

In one recent case, a 64-year-old patient with a history of breast cancer was initially diagnosed with metastatic carcinoma consistent with her breast cancer history. The tumor was above the clavicle. Using traditional methods, the tumor was studied for Estrogen Receptor, Progesterone Receptor and HER2. All were negative. The cancer did not appear to be breast cancer and therefore was classified as a TUO. Using the US LABS Gene Expression Profiling, the sample was compared to over 90 percent of known cancers and its three closest neighbors were identified. The findings were that the patient appeared to have adenocarcinoma of the stomach with a possible origin in the pancreas. Of course, treatments for this cancer are far different than those appropriate to the originally diagnosed breast cancer.

Tumors of unknown origin are the eighth leading cause of cancer in the United States. Most important, however, having a TUO is a critical situation for a patient in that it can slow the time to a correct treatment. Gene Expression Profiling provides a significant step toward closing that gap.

About the author:
Dr. James Thompson is senior medical director of US LABS, a leading cancer reference laboratory.

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