Many cancers are relatively easy to treat if detected early enough, but are usually missed because symptoms don't appear until they have spread. So the announcement of a test that can pick up eight forms of cancer before they would otherwise show up could be life-saving for many people. The trial delivered much better results for some cancers than others, but had enough hits to create great optimism.
An international collaboration led by Johns Hopklns University have created a dual method to reveal the presence of early-stage cancers and named it CancerSEEK. It combines a search for proteins released by the cancers (similar to the PSA tests used to detect prostate cancer) and assays for gene mutations commonly associated with disease.
Between these two methods, the research team hoped to facilitate early detection of cancers of the breast, colorectum, esophagus, liver, lung, ovary, pancreas, and stomach.
In Science, the inventors of CancerSEEK have announced the results of a study of 1,005 patients who had already been diagnosed with one of these cancers. As the authors note, the eventual aim is to identify cancers before other indications have alerted doctors to their existence, and this is likely to be harder than for those participating in the trial. Nevertheless, those whose cancers are already known represent a good place to start.
CancerSEEK picked up 78 percent of stage III cancers in the trial and 73 percent of stage II, but the success rate was only 43 percent for stage I. These figures, however, are averaged across all eight cancer types. For liver cancer, the success rate was 100 percent, while only 20 percent of stage I esophageal cancers were detected.
Equally importantly, the other component of the trial indicated that CancerSEEK doesn't have a high rate of false positives. Where the PSA is heavily criticized for indicating cancer in 9 percent of cases where none is present, less than 1 percent of cancer-free controls screened with CancerSEEK returned positive results. Besides preventing enormous distress, avoiding false positives also means not wasting enormous resources on follow-up tests for diseases that are not there.
CancerSEEK certainly meets a need. "While screening tests for some cancers have already been developed, and are associated with earlier diagnosis and better outcomes, for many major tumor types there are no effective screening tests,” said Professor Peter Gibbs of Australia's Walter and Eliza Hall Institute, one of the paper's authors, in a statement. “The currently available screening tests can also be unpleasant, have associated risks and uptake can be low. Significantly each test can only screen for one cancer at a time." Five of the cancers in the study currently lack any screening test at all.
The paper carries a prediction that CancerSEEK should be available for $500 per person, making it realistic for the regular testing of members of the general public in appropriate age-groups and not just for those at increased risk of one of the relevant cancers.
Besides the question of its sensitivity early in the development of cancer, the authors acknowledge other potential issues that may make the test less reliable as a general rule than in the trial's idealized circumstances. The cancer-free subjects in the trial were all healthy in other ways as well, meaning no inflammations can interfere with the results. Moreover, roughly equal numbers of people with each type of cancer were included in the trial in order to improve statistical reliability, but on average CancerSEEK proved less likely to detect the most common cancers, lowering the anticipated proportion of disease that will be picked up in general use.
An even larger study is now underway, and Professor Gibbs told The Age that demand is so high that CancerSEEK could be widely available even before the research is complete.
In some cases, CancerSEEK can only identify the presence of cancer, without distinguishing which organ is affected. However, the test in 63 poercent of cases can already identify the cancer's location, eliminating the cost and dangerous delay that follow-up tests would involve. In another 20 percent, CancerSEEK was able to narrow the possibilities to just two organs.