Recently, news stories in the media have highlighted a study from West Australian researchers reporting their work in developing a blood test that can detect early stage melanoma skin cancers. Early detection and treatment are key to curing melanoma.
Skin cancer is the most common cancer diagnosed in the United States. While melanoma is the least common form of skin cancer, making up 1% of all skin cancers, it causes the majority of skin cancer deaths.
Currently, melanomas are detected by visual inspection of the skin either by being noticed by the affected person or by a healthcare practitioner doing a skin examination. Confirmation of the diagnosis of melanoma can only be made by microscopic examination of a skin biopsy by a pathologist. Most melanomas are first treated by surgically removing affected areas. If the melanoma is detected in its early stages of growth, surgery will likely cure the cancer. While research is still very preliminary, a reliable screening test could potentially increase the number of melanoma cases detected before the cancer spreads.
In developing a blood test, the Australian researchers have used a high-density protein microarray—a laboratory technique that allows for testing large numbers of proteins at the same time. The microarray contained 1,627 different human proteins, many of them known to be involved in the development or progression of different types of cancers. By testing blood samples from people with melanoma and healthy controls, the researchers were able to identify antibodies in the subjects' blood against some of these protein antigens. Antibodies to specific proteins are early indicators of melanoma because they are part of the body's initial immune response to tumors. Previous research has shown that increased levels of antibodies to cancer antigens can be detected in the blood months to years before signs and symptoms of a tumor become apparent.
A total of 245 blood samples were tested, including 124 samples from people with early stage melanoma and 121 samples from healthy people. All samples from both healthy controls and people with melanoma contained a range of antibodies. Using statistical methods, the researchers were able to identify a panel of 10 antibodies that enabled them to identify most people with melanoma. This combination of markers identified 79% of people with melanoma, including very early stage melanoma skin cancer. This means that of every 100 people with melanoma who are tested, 79 will be identified and 21 (1 in 5) will be missed. The specificity or true negative rate of the test was 84%. This means that of every 100 people without melanoma who are tested, 84 will be correctly identified and 16 (1 in 6) will be labelled as possible melanoma.
These figures are encouraging but not ideal for a screening test. To be effective in screening the general population for early melanoma, the test would need to be much more sensitive and specific. It would need to identify a higher percentage (e.g., 95% or higher) of true positives and rule out a higher percentage of true negatives.
The authors also point out that so far melanoma patients have only been compared with healthy controls. In practice, some of the people being tested will have other diseases such as different kinds of cancer and other disorders, such as autoimmune diseases, which may have the potential to cause false-positive results and reduce the specificity of the test even further.
Nevertheless, this is an important advance as this is the best performing blood test to detect early melanoma so far. Further work may be able to improve the test performance and allow it to be used for patients in clinical practice.