For many cancer patients and their families, five years have become the magic number, after which they heave a big sigh of relief. It's also common to read that if you've been in remission for that period of time, you are 'cured".
But there is no magic number. True, 'five years' seem to be the plateau of the disease-free survival curve for most patients with different cancers.

In other words, most cancers in remission do not relapse after five years. If you remained disease-free for five years, it looks like you are cured.

But some cancers are very aggressive. We do not even need to wait for five years to declare, in such a case, that a patient in remission is cured. For example, in small cell lung cancer, once the patient has had a second year without evidence of the cancer, it is fairly certain he will not relapse. This particular cancer cell grows very rapidly. So, if it were going to recur, it would have done so very early in the course of the illness.

On the other hand, there are other cancers where the five-year mark is not really useful. One of the better examples is breast cancer. Patients can have a recurrence well after the fifth year. It is very frustrating for patients who have a recurrence after the fifth year because they thought that they have already been 'cured".

I remember one patient very well. I looked after her in 1996 and treated her for an aggressive lymphoma (called 'diffuse large cell lymphoma").

She was chatty and active. At 68, her eyes were still sharp, her haircut short. She used to gossip with me in Mandarin and Teochew. She completed six cycles of chemotherapy and achieved remission four months after treatment. And to our delight, she remained well for a very long time.

Initially, the follow-up visits were frequent: once every month or two. Through the years, the interval got longer and longer.

After about eight years, she disappeared. She no longer came because she thought that she had been cured. And so did I.

Last year, she saw her GP for an unexplained fever. Despite antibiotics, her fever persisted. When her GP mentioned that there was a small chance that fevers may be caused by cancer, she came to see me the same day.

We found a small lump in the abdomen, which we sent for a biopsy. Lo and behold, it was a lymphoma of the exact same type. By definition, this patient has been cured and the lump is considered a new cancer. But, with it being the same type, one has to consider that this is, in fact, a late relapse. She was treated and is again in remission.

I called up Saul Rosenberg, an eminent oncologist and an old friend in the United States, after confirming the diagnosis. Saul is also Professor of Medicine at Stanford University Medical Center and considered the Father of Lymphoma.

He said: 'PT, it just shows that you are getting older. With time, you will begin to see patients whom you have discharged come back with recurrent disease or new cancers many years after they are cured."

The odds of relapse after five years depend on the type of cancer. In breast cancer, about 10 to 15 per cent of patients who are disease-free after five years may still have a recurrence.

In most other cancers, the risk of relapse is so low that there are no studies done to determine how these late relapses can be prevented.

Because of the chance of a relapse, people get leery of saying that they are cured of cancer.

But the truth is, cancer can be cured. There are many cancer patients who beat their disease, live to a ripe old age and eventually die of non-cancer related illnesses. The earlier the stage of cancer is diagnosed, the higher are the chances of a cure.

At the same time, it is also true that cancer patients are more prone to new cancers. In December of 2006, I saw a patient who had stage II colon cancer four years ago and was recurrence-free, but discovered that she now has breast cancer.

The five-year mark is certainly something for cancer patients to aim for. Most cancer patients who reach this point are indeed cured. But there will be patients who relapse.

Naturally, there are a few who are upset and ask: 'Why me - again?"

Then there are others who are thankful for the bonus years of good health and prepare themselves to do battle, yet again.

Dr Ang, the medical director of Parkway Cancer Centre, has been treating cancer patients for nearly 20 years. In 1996, he was awarded Singapore's National Science Award for his outstanding contributions to medical research.

This article was first published in Mind Your Body, The Straits Times on May 21, 2008.