SINGAPORE - Dad, do you prefer to travel on the North South Line or the East West Line?" asked my teenage daughter, Victoria, as we strolled through the gantry of Botanic Gardens MRT station, which lies along the Circle Line.
We were making our way to City Hall MRT station for a weekend outing.
"East West Line. Better view," I replied.
I prefer the vantage point of travelling on the above ground tracks compared with the underground sections.
Cancer makes use of a similar transport system in our body to spread - minus the view.
Within half an hour, Victoria and I reached our downtown destination.
Despite the occasional grumble, most of us are fairly proud of our MRT system, for it gets us to places fairly quickly.
Cancer, fortunately, would typically take more than half an hour to spread from its site of origin. They usually take months to do so. But the cancer train network is way more extensive than our real-life transport system.
We call this cancer train network the lymphatic system.
"What are lymph nodes?" asked Ms T with a puzzled expression.
Ms T is a Chinese lady in her late 40s who was recently diagnosed with cancer in her left breast.
Her surgeon, following an operation to remove the cancerous lump, told her that her cancer had spread to the lymph nodes under her armpit, known as the axilla.
"Lymph nodes are the stations of the cancer train system," I explained.
Most people would be fairly well acquainted with the body's blood circulation system.
This system transports oxygen from the lungs and nutrients from the gut to the rest of the body. It also channels waste products from all parts of the body to the kidneys so that they can be excreted.
This blood transportation system is critical to sustaining life.
A lesser-known parallel transport system of the body is the lymphatic system.
The lymphatic system is a network of fine channels - somewhat similar to a train system - that takes up fluid that has inadvertently leaked out of the blood system and returns it to the heart.
Cancer cells may exploit this system to travel to all parts of the body.
Along the lymphatic channels are "stations" known as lymph nodes.
Cancer cells that have escaped their original site of growth and are travelling along these fine channels may be filtered out and become lodged in the lymph nodes.
That is why, if cancer cells are detected in at least one lymph node station, it means that they have managed to board the cancer train. A few cancer cells may have alighted at the lymph node station under scrutiny, while many more may be gleefully making their way to further destinations in the body.
The further the cancer cells spread, the more advanced the stage of disease.
The criteria that determine the stage of a cancer vary, depending on the site of origin.
Broadly speaking, cancer that is confined to the site of origin is in the early stage.
Once the disease escapes into the lymphatic system, it enters the intermediate stage.
Cancer that has reached other organs of the body is considered to be in an advanced stage.
Purging through chemo
It quickly dawned on Ms T that her cancer was in the intermediate stage and getting rid of the breast cancer cells from the original site of her left breast as well as those that alighted from the cancer train at the first station through surgery was not good enough. I had to help her purge the cancer cells from the entire cancer train system and beyond.
This I did through the use of chemotherapy.
Chemotherapy, when infused or ingested into the body, courses through both the blood and lymphatic circulation to rid the body of cancer cells that had escaped the site of origin.
Many of my patients who are totally cured of cancer went through a similar rite of passage.
I had to, through chemotherapy, figuratively pursue the cancer cells fleeing on the cancer train network - from Joo Koon in the west to Pasir Ris in the east, from Woodlands in the north to Marina Bay in the south.
After an enjoyable outing, Victoria and I, lugging several shopping bags, boarded the MRT to go home.
This is where the similarity with the cancer train system ends.
Tragically, cancer does not make this return trip once it is on the cancer train.
Dr Wong Seng Weng, medical director of Singapore Medical Group's The Cancer Centre, has been looking after cancer patients for the past 18 years.
He is also an adjunct clinician scientist at the Institute of Bioengineering & Nanotechnology at the Agency for Science, Technology and Research. He was a Lim Boon Keng and Tan Siak Kew scholar at the National University of Singapore
Get a copy of Mind Your Body, The Straits Times or go to straitstimes.com for more stories.