By Elise Garcon
In their early stages, cancers such as ovarian or lung cancer are difficult to detect, remaining asymptomatic and indolent until they are lethal. It is no wonder, therefore, that liquid biopsies, a screening tool that can pick up these cancers at very early stages, are a seductive prospect.
These are simple: blood samples undergo screening for DNA shed by tumour cells. An example of this is CancerSEEK, developed at John Hopkins University, which is undergoing the first large study of a liquid biopsy assay in a cancer free cohort of 10,000 women, between the ages of 65 – 75. It has detected 26 previously unknown tumours, presenting promising evidence in favour of the technology. However, the frequency of false positive results is unusually high.
CancerSEEK found double the number of types of cancer than conventional screening
Out of the 10,000 biopsies, 101 returned with false positive tests that lead to unnecessary invasive procedures. It is also unclear if the early diagnosis saved lives; although the earlier the cancer is detected, the higher the chance of survival, some tumours may remain benign and never require treatment. This can cause anxiety in patients, as well as using superfluous medical care. To reduce the frequency of false positives, a second blood test is administered to confirm the presence of abnormal DNA. CancerSEEK analyses 16 genes for mutations known to be associated with cancer, as well as detecting nine protein biomarkers which indicate that cancerous cells are present in the body. After this, a PET-CT scan is administered to localise the cancer.
Over the course of the study, CancerSEEK found double the number of types of cancer than usually found with conventional screening. The test has a sensitivity of 27.1% across all cancers and 31.1% for seven that currently have no screening options. Combining CancerSEEK with current testing resulted in a sensitivity of 52.1%, which represents the doubling. Seven of the cancers were of the lethally asymptomatic type, discovered in their early stages, and of the 26 women, most are currently undergoing treatment or are in remission, disputing the concern of unneeded early diagnosis.
Liquid biopsies could save thousands of lives from asymptomatic cancer
However, a worrying discovery was found in a year-later follow up of the study: the test had also produced false negatives. Breast, lung, and colon cancers were found in 24 women whose CancerSEEK was negative. However, the Hopkins research group maintain that the test, which continues to be developed, is intended to be ‘additive and complimentary’ to standard screening, and refute the opinion that people would shun other, proven screens if an easier liquid biopsy was available.
Larger tests in a more diverse population with matched control groups are required after the current study, which is planned to run for four more years. Thrive, the company with the rights to develop the test, raised $110 million last year, and is planning a large follow up trial designed to earn regulatory approval. Some question whether liquid biopsies will require long term studies to show survival benefits, meaning it could be decades before screening guidelines are set. One thing is known for sure: if the specificity of the test is increased and the errors reduced, liquid biopsies could save thousands of lives from asymptomatic cancer, which are preventable in their early stages.
Image: Bert Arnett via Flickr