Global Health Asia-Pacific July 2022 - Page 50

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One significant drawback of liquid biopsy , however , is that cancer DNA in the blood is often present in only small amounts , especially in early malignancies . received the green light from health authorities and will enable doctors to select the most effective treatment option . One example is the Guardant360 test , which can detect the genetic profile of several solid tumours ( including in the lungs , colorectum , breast , and prostate ), thereby helping doctors understand which therapy is more likely to benefit each individual patient .
In the case of breast cancer , for instance , this guidance can be extremely important for patients who initially test negative for the gene called human epidermal growth factor receptor 2 ( HER2 ), which promotes cancer growth . This is because , even though some patients ’ cancer may be negative , this can evolve and become HER2-positive over time , especially when they spread to other tissues . Hence , liquid biopsy can come in handy to check the HER2 status , giving patients with a HER2-positive cancer the chances of receiving specific medications that target the uncontrolled growth caused by HER2 such as monoclonal antibodies and kinase inhibitors .
“ That ’ s a powerful argument that these tests are useful to help monitor cancer ,” stressed Professor Shaw .
Despite their huge potential to detect cancer early , however , more research is needed to determine whether blood�based tests can benefit patients in the clinic , meaning that those who undergo them live longer compared to patients with cancer who don ’ t .
“ We need evidence from more trials with longer follow-ups to see if there ’ s an impact on overall survival . We don ’ t really know that yet ,” acknowledged Professor Shaw , adding that preliminary results look promising .
For instance , one study presented last year at the San Antonio Breast Cancer Symposium showed that selecting treatment based on liquid biopsy genetic analysis could double progression-free survival .
Tissue versus blood biopsies Though the same information is now typically obtained through a standard tissue biopsy where bits of cancer cells are surgically extracted and then analysed in the lab , opting for a liquid biopsy has some distinct advantages .
First , it ’ s less invasive and done through a conventional blood draw , avoiding the discomfort that patients face when tissue is taken out through a needle or surgery . “ Patients with metastatic cancer may not want to or be able to have a tissue biopsy ,” said Professor Shaw .
Unlike a standard biopsy , a blood test can also be repeated many times , allowing doctors to keep track of any genetic changes in cancer cells in real time in a way that could help improve disease management .
In addition , any tissue biopsy is potentially subjected to sampling bias because different bits of cancerous tissue might have different genetic profiles , while liquid biopsy offers a more insightful overview of the disease because it collects DNA from multiple cancer cells in the body .
Finally , not all cancers can be biopsied in a conventional way , either because it ’ s too risky or the tumour is difficult to access .
�ne significant drawback of liquid biopsy , however , is that cancer DNA in the blood is often present in only small amounts , especially in early malignancies . This makes it an approach that is usually employed in patients with advanced cancer — a stage where bits of cancer cells are more likely to be flowing in the bloodstream — to determine if they ’ re good candidates for targeted treatments or understand their prognosis , Dr Bert Vogelstein , a cancer geneticist at the Johns Hopkins Kimmel Cancer Center , told Cancer Today .
“ In general , if there is tissue available , it ’ s preferable to look at tissue to identify genetic alterations rather than looking in the plasma ,” he said .
Is a liquid biopsy screening test on the horizon ? Liquid biopsy has also made headlines for its promise to screen asymptomatic individuals for several types of cancer — a breakthrough that would provide a practical screening method for a variety of cancers , potentially improving early detection across the board .
One example is the Galleri test developed by Grail , which can be prescribed by doctors in the US under an FDA waiver for people at risk of cancer , like those aged 50 or older . The test helps detect more than 50 types of cancer in combination with other screening methods , since positive test results don ’ t necessarily mean patients have cancer .
Galleri blood test
48 JULY 2022 GlobalHealthAsiaPacific . com