London, UK: An analysis of new data by a leading cancer researcher has revealed specific cancers that are most likely to affect teenagers and young adults, and it points to infections, adolescent growth spurts, and hormones as being among the possible causes. Now, international collaborative research is needed to find out more.
Professor Jillian Birch told a news briefing at the 4th International Conference on Teenage and Young Adult Cancer Medicine, organised by the charity Teenage Cancer Trust, that her analysis of a new data set [1] of more than 1.6 million cases of cancer in people aged between 0 and 79 in England during the period 1995-2003 showed that there was a category of cancers that had a peak incidence between the ages of 13 to 24.
"These can be regarded as 'true' teenage and young adult cancers that typically occur specifically in this age group, rather than being either the tail-end of childhood cancers, the majority of which occur below the age of 10, or the unusually early development of cancers typical of older ages, most of which occur over the age of 60," said Professor Birch, who is Cancer Research UK Professorial Fellow at the University of Manchester.
"We already knew from our earlier research that the most common groups of cancers in teenagers and young adults are lymphomas, germ cell tumours, leukaemias, brain tumours, bone tumours and soft tissue sarcomas. However, unlike the childhood embryonal tumours, these groups of cancers can be seen at all ages. This new research shows that there are specific types of cancers within these groups that show a main peak of incidence in 13 to 24-year-olds. These are: Hodgkin lymphoma, osteosarcoma, Ewing sarcoma, certain rare soft tissue sarcomas (such as alveolar soft part sarcoma), germ cell tumours of the testis and ovary, and germ cell tumours in the brain.
"These tumours together represent one third of all cancers in 13 to 24-year-olds."
Professor Birch said that the pattern of incidence had implications for discovering and understanding the causes of teenage and young adult (TYA) cancers.
"It is a frequently held view that there is no such thing as 'teenage cancers' in the sense that embryonal tumours typify cancers of early childhood. Our research shows that there is, and, having identified the very specific types that are TYA cancers, we are able to find clues as to why teenagers and young adults get cancer. These point to infections, adolescent growth spurts, hormones and other growth and development factors as among the most probable causes.
"Considering these 'true' TYA cancers, there is quite a lot of evidence suggesting that infections, particularly the pattern and timing of infections, are causally involved in Hodgkin lymphoma. While the Epstein-Barr virus has been implicated already, this would only account for a proportion of cases. Other infectious agents involved in causation of Hodgkin lymphoma have yet to be discovered.
"Osteosarcoma is a tumour that occurs predominantly in the long bones of the legs (73% of all cases) and arms (10% of all cases) and has a very pronounced peak of incidence during the teenage years. There is a slightly earlier age peak of incidence in girls than in boys, coinciding with the adolescent growth spurt. We can speculate that pre-cancerous genetic changes occur in the bone tissue during childhood and that during periods of rapid growth in teenagers, further genetic damage occurs, resulting in conversion of pre-malignant cells to malignant, leading to the formation of a bone cancer. A similar age of onset pattern is also seen for Ewing sarcoma of bone and the causal mechanisms may be related.
"Most testicular cancers, at whatever age, are germ cell tumours and it is well known that these show a peak incidence in young adult males. In contrast, most ovarian cancers are carcinomas (cancers that arise from the epithelium), and ovarian cancers in general show a peak incidence over the age of 60. However, our analysis has demonstrated that germ cell tumours of the ovary are most frequent in older teenagers. Furthermore, the same is true for germ cell tumours in the brain. It seems possible that hormonal and other factors affecting growth and development before and after birth are implicated in the development of germ cell tumours."
Professor Birch was able to reach these conclusions because of the way she analysed the data. "The data set included over 14,000 cases in 13 to 24-year-olds. Normally cancer statistics are presented in terms of the site in the body at which the cancers occur, but this is not satisfactory for cancers in young people which tend to be more specialised, and therefore we analysed the data set according to the types of cells and tissues involved in the cancers."
Cancers in teenagers and young adults are rare, but they are the leading cause of death, after accidents, in this age group. In the UK, there are about 1,900 new cases each year [2], and in England there are about 1,600 new cases, including an average of 230 Hodgkin lymphomas, 46 osteosarcomas, 40 Ewing sarcomas and 230 germ cell tumours. These small numbers make it difficult for researchers to investigate the causes properly and Professor Birch called for international collaboration in order to obtain the large numbers needed.
"In order to develop and explore our ideas about the causes of TYA cancers, we need international collaborative studies. Such studies should incorporate biological analyses, as well as more classical approaches, and should consider the mechanisms by which the cancers start, as well as the causes. Until we understand the causes and mechanisms of TYA cancers it will be difficult for us to make significant progress in preventing them and treating them more effectively," she concluded.
Notes:
[1] Data provided by the National Cancer Intelligence Centre, Office for National Statistics, London.
[2] Jill Birch's figures exclude carcinoma in situ of the cervix and non-melanoma skin cancers. They are the most up-to-date figures on incidence available for this age group and supersede previous estimates.
Glossary:
1. Embryonal tumours are usually malignant tumours that arise from the rudiments of an organ or from immature tissue during intrauterine or early postnatal development.
2. Ewing sarcoma is a malignant bone cancer.
3. The Epstein-Barr virus is a member of the herpes family of viruses and the cause of glandular fever.
4. Germ cell tumours begin in cells that, in a developing foetus, become sperm or egg cells. Because of the way a baby develops in the womb, these kinds of tumours are found in the ovaries and testes, and in other sites along the midline of the body, such as the brain.