Children's Cancer in Hong Kong - Present Situation and Future Development

Dr. Li Chi Kong
The Lady Pao Children's Cancer Centre
Department of Paediatrics
The Chinese University of Hong Kong

Children cancer is not a common disease. In Hong Kong, there are only about 150 newly diagnosed cases of cancer in children each year. This is less than 1% of all cancer cases in Hong Kong. But the disease is the No.2 killer of children above the age of one, second only to accidental deaths. At present, an average of 40 children died of cancer every year. Statistics show no significant increase in children cancer cases in Hong Kong in recent years (Chart 1).

1. Types of cancer

The types of cancer common among children are very different from those afflicting adults. The 10 most common cancer diseases in adults are rarely found in children.
Acute leukaemia, or blood cancer, is the most common among children cancer diseases, accounting for about 35% of all cases. In second place is brain cancer, followed by lymphoma (cancer of lymphatic tissue). These 3 diseases together account for 60% of all children cancer cases. The remaining 40% of the cases can be divided into 8 categories, including neuroblastoma, Wilms' tumour and bone tumour. The pattern is more or less in line with that of Western countries. According to records of the Hong Kong Cancer Registry, local children are slightly less susceptible to Wilms' tumour and Ewing's sarcoma than Caucasian children. Whether this is due to genetic difference has not been confirmed.

2. The Cause

The cause of children's cancer has largely remained unknown although decades of research has greatly increased the understanding of cancer. For instance, research in genetics and molecular biology has revealed that most of the patients experienced certain genetic mutations. But such changes are not hereditary and to discover the cause has become a hot topic of medical research. Most medical scientists believe that cancer is caused by "multiple-hit effects". Cancer is triggered not only by genetic changes that take place in the body but also by external carcinogens and some other unknown factors. The connections of carcinogens and adult cancer are obvious. For instance, smoking is often linked to lung cancer and hepatitis B to liver cancer. But up to now, a common carcinogen for children cancer has not yet discovered. To be sure, radioactivity is a known cause of cancer. However, people are rarely exposed to harmful doses of radioactivity. There have been much talk in recent years about the link between mobile phones and brain cancer. However, most research works done on the subject tend to dismiss such a link. Although many children's cancer cases happen before the age of 5, there is not established link to hereditary factors except for very few exceptional cases, such as Down's syndrome and leukaemia, or retinoblastoma.

3. Diagnosis

The treatment of cancer is not simple. Different treatments can cause different short-term or long-term side effects. Therefore, it is imperative to make a precise diagnosis to ascertain the spread, or the "stage", of the cancer disease before prescribing the most appropriate treatment that must be neither too mild nor too drastic. The general approach to diagnosis is the histological examination of the affected tissues (examine under microscope).

To diagnose leukaemia, the best way is to examine the bone marrow tissue where the disease originates. For other cancerous diseases, the approach is to test tissue samples of the tumour. These tissues can be obtained through operation to remove the tumour or, more commonly, by inserting a needle into the tumour to obtain tiny samples for testing. This is a faster and less traumatic way to diagnose the disease. To examine whether cancerous cells have dispersed requires the use of radiological investigations such as X-rays, ultra-sound scanning of the abdomen, CT scan of brain and lungs, and magnetic resonance imaging of the tumour and its surrounding area. Radio-isotope bone scan is scanning of the entire bone structure. Bone marrow tests are not limited to leukaemia. In diagnosing other cancers, one must bear in mind that other cancerous cells can also spread to the bone marrow.

4. Therapy

1) Surgical removal of the tumour is still the surest way to treat many children's cancer. This is particularly effective on brain tumour and neuroblastoma. If the tumour can be successfully removed, the chances of recovery will be greatly increased. Tumours that are too large or located too close to the main blood vessels or other vital organs cannot be surgically removed immediately. In such cases, it is necessary to apply chemotherapy before surgically removing the tumour completely. Most children patients respond well to this treatment. Tumour in the liver or those situated close to the main blood vessels simply cannot be operated on even after chemotherapy. The only alternative is to replace the affected organs. But organ donation is not widely accepted in Hong Kong. Many people in Hong Kong are not willing to see the donation of their deceased relatives' organs. As a result, development in this area has been sluggish.

The advance in surgical operations on children's cancer has made rapid progress in recent years. For instance, amputation is no longer necessary in most bone cancer cases. The defect left by the removal of the bone tumour can now be filled by human bones from the bone bank or synthetic materials. This way the affected limb can be preserved. The advance in brain surgery is particularly swift. With the help of computers, a brain surgeon can now input the images scanned from the patient's brain into the machine which will enable him to make precise incisions during the operation. Another major progress in surgery is the combined use of miniature apparatus and the laparoscope to perform operation through a few small openings to remove a tumour or extract tissues for testing. This can minimize post-operation pains and ensure more rapid recovery. Nevertheless, this procedure cannot be used in all tumour surgeries.

2) Radiotherapy: Radiotherapy is widely used in treating cancer diseases, especially for adults. It is less frequently used on children cancer patients. Many people wrongly believe that radiotherapy is a painful process. In reality, it is quite similar to having an X-ray taken. The only difference is that a session of radiotherapy takes longer, a few minutes to over 10 minutes, to complete than X-ray. The process is not painful at all. Leukaemia is the most common cancer diseases among children. Some 20 years ago, radiotherapy was prescribed to all leukaemia patients to prevent the relapse in the central nervous system. But patients subjected to long periods of radiotherapy developed myriad problems, including brain damage, disruption of hormone secretion and, in serious cases, even brain cancer. The damage done by radiotherapy to children patients can be even greater because it can inhibit growth by destroying the soft tissues of the bones and muscles. Nowadays, radiotherapy is less commonly used on children cancer patients. Other methods are used to enhance the effect of chemotherapy on the brain tissues to prevent relapses. However, radiotherapy has remained the only effective method to bring certain types of cancer under control. It is applied to the affected area after surgery to minimize chances of relapse. In cases such as neuroblastoma and rhabdomyosarocoma, the tumours are located in areas that make it impossible for surgical removal. The only alternative is to administer massive doses of radioactive ray to destroy the cancerous cells. Radiotherapy is also essential to destroying certain brain tumour or Ewing's sarcoma. The development of new technology and medical equipment has greatly increased the effectiveness of radiotherapy and minimized its harmful side effects. For instance, advanced computerization has enabled more precise focusing of the radioactive rays on the tumour. Such accuracy allows for administering very high doses on the tumour without fear of damaging the surrounding healthy tissues. It works just like laser surgery. Radiotherapy is also applied to the terminally ill patients to relieve the pain caused by cancer.

3) Chemotherapy: Chemotherapy is effective on most children cancer patients. Some cancer diseases, including Lymphoblastic Leukaemia, can be cured just by chemotherapy. These cancer diseases are characterized by fast growing tumour against which chemotherapy is particularly effective. Many types of tumour can only be destroyed by a combination of treatment programmes such as surgery and chemotherapy or surgery plus radiotherapy or radiotherapy together with chemotherapy or all three. This is particularly true in the case of solid tumour. Chemotherapy has two effects on a solid tumour. One is to shrink the tumour and the other is to destroy any remaining parts or the spreaded cancerous cells. Some tumours are large and have many blood vessels running through them at the initial stage of the disease. For that reason, surgical removal of these tumours is highly risky. Moreover, it will not be possible to have these tumours removed completely. Chemotherapy can shrink the tumours and reduce the abnormal blood vessels in them. After 3 or 4 courses of chemotherapy, it will be relatively safer for the surgeon to operate on the patient to remove such a tumour completely. This combined treatment method is often used in the treatment of Neuroblastoma and bone cancer. One characteristic of cancer disease is the spread of cancerous cells to other organs in the body though blood vessels and lymph glands. Such spread often takes place in the early stage of the disease. Despite the advance in diagnostic technology, such as magnetic resonance imaging and radioisotope scan, tiny spread is not always detected. Past experience shows that surgery alone, or terminating chemotherapy too early could cause recurrence in many patients that greatly reduces the chance of recovery. For that reason, chemotherapy is included in the treatment of the vast majority of children cancer patients. This is part of a comprehensive treatment programme to completely destroy the cancerous cells and achieve a permanent cure.

There have been much research into enhancing the effectiveness of chemotherapy to raise the chances of curing cancer diseases. Some cancerous cells are more resistant to chemotherapy than others. A combination of various different drugs are needed to destroy these cancerous cells. Every year, new anti-cancer drugs are being developed giving patients new hopes. However, the development of these new drugs has become a driving force behind inflating medical costs. Unfortunately, there is no guarantee that these new drugs can cure cancer. What many of them can do is to prolong the lives of patients by controlling the growth of cancerous cells in their bodies.
Chemotherapy has many side effects, including vomiting, hair loss and suppression of the bone marrow causing infection and bleeding. There are many drugs available now to help minimize the side effects of chemotherapy. Some can prevent vomiting and some can hasten the production of blood cells. All these drugs are designed to minimize the discomforts and side effects of chemotherapy making it possible for the completion of the treatment programme to proceed according to schedule.

4) New Treatment Methods

(1) Immune therapy: Severe side effects of anti-cancer drugs place a limit on the dosage that can be used. As a result, much research work has gone into achieving better results in clearing cancerous cells through immune therapy. This involves, for instance, the use of antibodies that target only cancerous cells without harming the normal tissues. In Hong Kong, these drugs have been tried to treat Neuroblastoma, but its long-term effect is still under investigation.

(2) Blood Stem Cell transplant: The basic principles are the same in the transplanting different types of blood stem cell, including bone marrow, umbilical cord blood (placental cord blood) and peripheral blood stem cell. Usually the first step is to clear as much cancerous cell in the patient as possible through massive doses of anti-cancer drugs or radiotherapy of the whole body. At the same time, steps must be taken to suppress the patient's immune system so as to enable the building of a new foreign bone marrow and immune system by the transplanted cells. If the cells come from another person they are called allogeneic. It is common used in the treatment of leukaemia. When the transplanted cells are harvested from the patient, the operation is called autologous, which is widely used to treat solid tumours. Stem cell transplant is not a cure for all cancer diseases. What is more, relapse can still occur after transplant. Transplant is also a high-risk treatment with potentially fatal complications. Some cancers may already have a higher than 70% success rate of cure by conventional methods, thus not all cancer cases need to be treated by cell transplant.

(3) Target Therapy and Gene Therapy: These are newly developed weapons in the anti-cancer treatment. Years of research has unveiled the secrets of the genetic chain reaction that creates cancerous cells. Drugs are being developed to stop the growth of cancerous cells by disrupting the underlying genetic process. These drugs are now being clinically tested. The great advantage is that they will have no effect on the normal cells. Initial tests on patients suffering from chronic leukaemia have produced encouraging results. But the long-term effectiveness has remained uncertain. Further studies are needed to ascertain whether they can completely destroy the cancerous cells.

5. Conclusion

With the advance in science, significant progress has been made in identifying the cause of cancer, its many permutations and treatment methods. More and more cancer patients are being cured. More than 70% of all children cancer patients have recovered without relapse in the long-term. The new drugs and methods have proven to be effective. But they are too expensive for many patients. Whether these patients must wait for the cost of new medicines to come down is a social issue that the government has to address.

Chart 1: Number of Children Cancer Cases in Hong Kong

Sources from Hong Kong Cancer Registry

Diagram 1: Types of Children Cancer

Note: No. of Cases Collected by Hong Kong Paediatric Haematology and Oncology Study Group from 1994 to 2000