Telling someone he has cancer is no easy task for most doctors, but I have done it so often and for so long that I have my script well worked out for most possible scenarios.

Even then, having to tell someone he not only has cancer but also Aids - Acquired Immune Deficiency Syndrome - is a different ball game.

My first such encounter was when I was working at Singapore General Hospital. The Chinese-speaking patient - a well-groomed, polite and affable man - was in his early 30s.

He had stage four malignant lymphoma or cancer of the lymphoid tissue, but he had responded well to chemotherapy.

At the time, we were considering a stem cell transplant for him. As part of the routine investigations, we tested him for antibodies to the human immunodeficiency virus (HIV).

It came as a complete shock to me when the laboratory called to notify me that he had tested positive.

'How could it be possible? There must be some terrible laboratory mistake. Maybe, he had a blood transfusion some time ago that I did not know about," I thought, as I steeled myself to call him to come and give another blood sample.

'I'm so sorry but there seems to be some mistake in your recent blood test. The test for HIV was positive so we need another sample to clarify the matter," I said.

His response was most unexpected. I assumed he would be shocked, angry or confused but he simply smiled and said: 'Okay."

Knowing that he was single, I asked if he had casual or commercial sex. He nodded and told me that he had been sexually active since his army days.

He visited a border town in Thailand frequently. Over the years, he had engaged the services of about 50 prostitutes.

With his compromised immune system, a transplant was out of the question. After his chemotherapy was completed, he transferred out of my care and started treatment for Aids.

We lost touch soon after that.

It is now routine for every patient with malignant lymphoma to be tested for HIV. In the hundreds of lymphoma patients I have looked after, I can recall fewer than 10 who have tested positive for HIV.

Any lymphoma patient who tests positive for HIV is considered to have Aids. This is different from an asymptomatic patient who happens to be tested positive, as he would only be an HIV carrier and not necessarily have full-blown Aids yet.

Aids patients have an impairment of their immune system. This means that their immune system cannot keep the body's well-being under surveillance, which makes them more prone to developing cancer.

The two commonest cancers in Aids patients are malignant lymphoma and Kaposi's sarcoma (a cancer that causes patches of abnormal tissue to grow under the skin, in the lining of the mouth, nose, throat or in other organs).

Other cancers that appear to be associated with Aids include Hodgkin's Disease (also a type of cancer of the lymph nodes) and cancers of the mouth, lungs, cervix and digestive system.

The treatment of cancer patients with Aids poses special problems. These patients are prone to infections, which strike only those who are already weakened by their underlying illnesses.

Doctors have to be careful not to be too aggressive with the treatment programme.

HIV poses not only medical, but also policy challenges. An interesting problem, one which used to frustrate me, was that foreign patients were barred from entering Singapore for treatment of their cancer once they were known to carry the virus.

Each time a patient is diagnosed with HIV in Singapore, the doctor is required to notify the Ministry of Health. In due course, the patient is blacklisted by the Immigration authorities and prevented from re-entering Singapore.

I managed to convince the authorities that this did not make sense. We have millions of visitors to Singapore each year and there is no requirement for them to declare their HIV status on entry into Singapore.

Some of these HIV carriers may indeed engage in illicit sex with locals and spread the disease.

On the other hand, cancer patients with HIV who come here have a genuine desire to seek medical care. To me, they pose a lower public health risk than tourists with HIV.

Thankfully, the Health Ministry has worked out waivers on a case-by-case basis, to allow foreign patients with HIV to come to Singapore for treatment.

These patients are fighting two diseases, one of which is highly infectious. For the patient, HIV is no different from cancer or any other disease - it, too, bears a crying need for treatment. Giving patients the same sort of choice appears to be the right thing to do.

angpt@parkwaycancercentre.com

Dr Ang, the medical director of Parkway Cancer Centre, has been treating cancer patients for 23 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.