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Blood test to reveal whether select prostate cancer patients will respond well to treatment

The test may also reveal genetic details identifying cancer risk for patient’s children.
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​In the not too distant future, a simple blood test established by BC Cancer’s Dr. Kim Chi and Dr. Alex Wyatt will help identify a group of prostate cancer patients most likely to benefit from a new, Health Canada approved treatment and may even detect if their cancer is a result of an inherited genetic abnormality – which could have implications on cancer risk for their children. 

This blood test, known as circulating tumour DNA assay, is suitable for patients with metastatic castration-resistant prostate cancer (mCRPC), a particularly aggressive form of the disease which develops in approximately 10 per cent of all people diagnosed with prostate cancer. The test would examine the circulating tumour DNA (ctDNA) within the blood to identify which of these patient’s cancers have genetic defects in the BRCA1, BRAC2 or ATM genes. 

“As aggressive cancer grows across the body, cancer cells are turning over and shedding their contents into the bloodstream,” says Dr. Wyatt, scientist with the Genome Sciences Centre at BC Cancer and assistant professor in the Vancouver Prostate Centre and Department of Urologic Sciences at the University of British Columbia (UBC). 

“We have developed new technology that can analyze tumour DNA present in a patient’s bloodstream, essentially giving us the same information we would collect from a biopsy but in a more efficient way that is easier on both the patient and the health care system.” 
This is especially true for people living in remote and rural communities whose neighbourhood lab or clinic could collect the samples for testing rather than having a patient travel to a hospital.

From this blood test, detailed information can be collected about the tumours including whether the cancer was originally caused by inherited genetic alterations, specifically BRCA1, BRCA2 or ATM defects or if the mutations are only present in the cancer itself. There are two significant implications to knowing these details. 

“Knowing what genes have been disrupted in a cancer can help oncologists determine the best course of treatment,” says Dr. Kim Chi, medical oncologist and chief medical officer at BC Cancer and professor of medicine at UBC. “This is especially important for patients with mCRPC because if they are given an ineffective treatment for their cancer sub-type, not only do they suffer the adverse side-effects of treatment, but their disease can get worse because it’s not being managed effectively.” 
Dr. Chi, along with an international team of cancer researchers and clinicians, has worked for years on a new treatment for mCRPC which recently received Health Canada approval. The treatment targets cancers with BRCA or ATM genetic defects by further inhibiting the DNA repair pathways that are already under strain from loss of BRCA or ATM function. Another important implication for testing for BRCA or ATM defects is that the test can detect if these mutations are genetically inherited; it is well documented that BRCA defects can cause breast and ovarian cancer.   

“We can now detect families who may be at risk of developing hereditary prostate, breast, or ovarian cancer,” says Dr. Chi. 

“Most prostate cancer patients are men in their 50s and 60s, and older – many of whom have children in their 20s and 30s,” adds Dr. Wyatt. “Those adult children, who may also be carrying defects in these genes, can take steps to reduce their risk of cancer by prevention methods including making adjustments to their lifestyle, being vigilant about screening or seeking medical assistance immediately if they develop symptoms later in life.” 
By knowing their risk, steps can be taken to prevent or detect hereditary cancer early; leading to improved health outcomes for generations. 

These insights come from a recently published study in Clinical Cancer Research led by Drs. Chi and Wyatt, which profiled blood samples from over 800 mCRPC patients, mostly from B.C., conclusively identifying cancerous defects in genes that help repair DNA, and will help identify new therapies like the one recently approved by Health Canada, that are effective for cancers caused by DNA repair defects. 

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