A technique that uses sounds emitted by cancer cells to detect the spread of the disease has been tested successfully by US scientists.
Given a diagnosis of skin cancer, it's crucial to establish whether the disease has already spread, as this determines the prognosis for the patient and how the condition should be managed.
One of the first places that cancers spread to, known also as metastasis, is the nearby assemblage of lymph glands.
By injecting a dye into the cancer, doctors can then remove lymph nodes that contain the dye - indicating that they must drain fluid from the region of the tumour - to see if these so-called "sentinel" lymph nodes contain cancer cells.
If they are tumour-free, then the likelihood that the disease has spread is very remote.
However, the current process is invasive and involves painful surgery, one side effect of which can be permanent swelling of the affected body part. This is a condition called lymphoedema.
Recently, scientists have developed a new technique, known as MSOT - multispectral optoacoustic tomography - that can use light waves to add energy to any cancer cells that are present and then listen to the sounds the excited cells produce.
The rationale is that certain cancers make large amounts of certain chemicals, which can be used as biomarkers to detect them. Melanoma skin cancers, for example, produce the brown pigment melanin, which has a characteristic sonic signature when excited using the MSOT technique.
Writing in Science Translational Medicine, University of Duisburg-Essen scientist Joachim Klode and his colleagues have now tested the technique on clinical specimens and on patients and shown that it can be used with apparently 100% sensitivity to screen for melanoma spread to a patient's lymph nodes.
In a small trial, a series of patients with confirmed melanoma first underwent imaging using the MSOT system, and then underwent surgery to retrieve the labelled sentinel lymph glands, which were then studied by a pathologist to look for any traces of cancer.
In this way, the performance of the existing "gold standard" sentinel biopsy technique could be compared with the newer experimental MSOT-based approach.
The MSOT results were 100% accurate in ruling out the spread of cancer. Negative findings by MSOT were supported in every case by the pathology findings.
The test fared less well at ruling in cancer, with a false positive rate of over 40%; even so, these parameters mean that the approach will not miss any cases and would, in the present form, spare half of patients from having much more invasive surgery to achieve the same result.
Now the work needs to be repeated in a bigger group of patients to prove that the results are robust. "If validated in larger studies, this approach could alleviate the need for invasive surgery in a significant number of patients," the team point out.