New test to prevent mistakes in cancer diagnosis

Chemists at the University of Technology, Sydney have developed a test that promises to reduce the number of false negatives in melanoma diagnosis, and potentially for other forms of cancer as well.

UTS Faculty of Science PhD student Alison Beavis has demonstrated that chemical testing can confirm to surgeons that they have removed the correct tissues for biopsy.

The key to success has been the presence of a particular metal, antimony, in a radioactive solution (colloid) used to track the potential path of cancer cells from a skin tumour to the nearest lymph glands.

"For the past decade cancer specialists have been using a very accurate diagnostic process called sentinel lymph node (SLN) biopsy, which identifies the first lymph nodes that would receive cancer cells," Ms Beavis said.

"When a skin cancer is removed the radiocolloid is injected at the site and the lymph node basin to which it drains is located under a special scanning device. Then, immediately before surgery a blue dye is injected into the site of the melanoma which stains the 'sentinel' lymph node blue.

"The surgeon removes the blue node and it is examined for the presence of cancer cells by a pathologist. If cancer cells are detected, a second operation is performed and all remaining lymph nodes are removed.

"SLN biopsy is a very complex procedure and there have been a small number of melanoma cases where the wrong lymph node has been removed and a false negative result given. Discovery of such an error has been difficult because the radioactive component of the radiocolloid breaks down very quickly and the blue dye disappears when tissues are prepared for pathology, so another quality assurance tool was needed.

"The first step was to look at the make-up of the radiocolloid and it was found that it contained antimony, which would be retained by the sentinel node. The rest has been applying basic chemistry to the problem."

After confirming that antimony is not found in high concentrations in body tissues for other reasons, the UTS team was given archive samples of 46 lymph nodes for testing - 22 from melanoma patients who had been injected with the radiocolloid and 24 from non-cancer patients who weren't exposed to the radiocolloid.

"We got perfect separation," Ms Beavis said. "Then, from 20 samples still available from known false negative cases, we were able to determine that five had been incorrectly identified as sentinel nodes."

Ms Beavis said more verification work must be done before the test is cleared for use in current melanoma cases, but it is hoped it will eventually be employed for any cancer where SLN biopsy is used, including breast cancer and cervical cancer.

The UTS team is also looking at different techniques, involving laser-assisted sampling, to speed up the analysis process and allow surgeons to get a result while the patient is on the operating table.

But, an intriguing limitation to the work being done in Australia is that it can't be applied in Europe and America.

"When radiocolloid standards were being decided some decades back Australia chose the antimony-based substance, while in Europe and America a sulphur-based colloid was chosen," Ms Beavis said. "Currently we can't detect tiny quantities of sulphur in a way that would make the test workable over there, but more sensitive instruments are being developed that could soon make it possible."

Item provided courtesy of UTS