As the next line of screening, a new nuclear imaging scan can detect prostate cancer cells even when they are too few or too small to be picked up by conventional tests.
According to a small pilot study by a team from Singapore General Hospital (SGH) and National Cancer Centre Singapore (NCCS), the test known as the gallium-68 PSMA ligand PET/CT scan is able to detect cancerous areas “accurately and quickly”, said Dr Winnie Lam, Senior Consultant, Department of Nuclear Medicine and Molecular Imaging, SGH.
“It is sensitive enough to be able to detect the presence of prostate cancer when the cancer cells are too few or too small to be picked up by conventional tests,” she added.
The test combines a radioactive material (gallium-68) with a novel ligand molecule, which has been found to bind easily with the prostate-specific membrane antigen (PSMA), a protein found on the surface of prostate cancer cells.
The radioactive substance is injected into the body, and travels through the blood stream to bind with prostate cancer cells. The radioactivity emitted by cancerous prostate cells shows up on the scan, indicating the diseased areas.
This type of scan is particularly effective in seeking out cancerous cells when the standard screening for prostate cancer – the prostate-specific antigen or PSA blood test – shows a relatively low rise in the level in the blood.
“Conventional imaging techniques have limited value in evaluating biochemical recurrence at low PSA values, detecting disease in only approximately 11 per cent of patients with PSA of less than 1.0 ng/ml [1.0 nanograms of PSA in each millilitre of blood],” said Dr Lam.
By comparison, the nuclear imaging scan was able to detect prostate cancer cells in 84 per cent of the 57 patients who underwent the nuclear imaging scan for biochemical recurrence between 2015 and June 2017 in the SGH study. In the group with PSA levels of 0.5 to 1.0 ng/ml, the detection rate was nearly 90 per cent.
The scan was also able to determine location of the cancerous cells – in the prostate area, lymph nodes, bones and other organs – and this allows for accurate treatment planning, said Dr Lam. When the clinician can’t determine where the cancer has recurred, radiotherapy is often performed in the prostate area presumptively.
The nuclear imaging test is used as an additional tool to detect prostate cancer if other tests are negative. A raised PSA level can indicate more benign conditions like an enlarged prostate or inflammation.
Prostate cancer is the third most common cancer affecting men in Singapore in 2011-2015, and ranks sixth in cancer deaths among men for that period, according to the Singapore Cancer Registry’s latest Annual Report.
The disease usually affects men past the age of 50 years. It has few signs in the early stages, and is usually picked up incidentally during routine examinations. When the disease is more advanced, complaints like difficulty in urinating or bone pain may surface. When cancer of the prostate, a small gland located below the bladder, advances, it tends to spread to the pelvis and the bone.
The nuclear imaging scan isn’t used just to check for a recurrence of prostate cancer. It is also able to “stage” newly diagnosed prostate cancer to find out how far it has spread. Unlike MRI, which can only determine the stage in a specific part of the body, the nuclear test scans the whole body, showing where cancer cells have gone beyond the prostate.
The SGH study was presented at the European Society for Medical Oncology Asia 2017 conference in Singapore last November. The team also included Dr Charles Goh, Associate Consultant, Department of Nuclear Medicine and Molecular Imaging, SGH; Dr Melvin Chua, Consultant, Division of Radiation Oncology, NCCS; and Dr Janice Tan, Medical Officer, MOHH.
SOURCE: THIS ARTICLE WAS FIRST PUBLISHED IN SINGAPORE HEALTH MARCH/APRIL 2018.
