For Dr Dennis Lim, the increase in the number of expats in Singapore over recent years has meant a parallel increase in the number of patients with malignant melanomas that he sees. In 2008, he formed a work group to streamline the management of the condition and explore the use of Sentinel Lymph Node (SLN) mapping and biopsy. It’s now an integral part of his treatment for patients with advanced-stage melanoma.
You treat far more expats for malignant melanoma than locals. Why are Australians, for instance, more prone to this type of skin cancer than Singaporeans?
Asians are genetically designed for the sun: we have evolved to have larger amounts of melanin in our skin. If a Caucasian and I were to go out in the sun today, he may burn very quickly and even have some dermal damage; my skin might darken slightly, but it would quickly return to normal.
Distribution of malignant melanoma is fundamentally different, too: Western expats tend to get skin cancers on the back and trunk – in the true sun-exposed areas – whereas locals tend to get them on their limbs and nail beds.
How deadly is malignant melanoma?
Melanoma is not a death sentence – in the vast majority of Western-type cases, a 30-minute operation cures the problem. Around 90 percent of melanomas (and I’m generally quoting US statistics here) are described as Stage 1, involving a short procedure and a reasonable follow up to treat the cancer.
What is your approach to more advanced cases?
I deal with Stage 3 and Stage 4 melanoma at my clinic. This is where this concept of SLN comes in. More commonly, SLN has been used in breast cancer cases. The theory is that if you have a group of cancer cells, the first place they spread to is the first-generation nodes and then to further-generation nodes. If I can identify the first lymph node that is negative for cancer – that is, the Sentinel Lymph Node – I can predict quite accurately that the others are not involved, hence avoiding a bigger operation.
How do you locate the SLN?
We inject a low-activity radioactive substance around the primary cancer, then we take a picture which shows the SLN where the radioactive material concentrates. I then use a gamma counter to look for the lymph node and I take it out.
It used to be that if you had a cancer at an advanced stage in the local site, we would take out all the lymph nodes at risk – about 15 or 20 – to explore the problem; but taking all these lymph nodes out involves a considerable physical impact for the patient. SLN aims to minimise this type of surgery.
How long does it take?
An SLN biopsy is done over several hours. First, it requires coming into the Nuclear Medicine Department of the hospital for the injection of the radionuclide, and subsequent imaging to localise the SLN. I then use a gamma probe to look for the SLN and remove it.
If the surgery is successful, what is recovery like?
In the short- to medium-term, there is some “nannying” of the wound. But removing one lymph node does not impact you very much. The majority of my patients in whom we have identified the “true” SLN go back to regular life.
For more information, call Dennis Lim Surgery at 6836 5167 or visit www.dennislim.com.sg.