Thirty years reviewed

Asthma patients would be particularly prone to lung cancer. Women more than men. These are the conclusions of a very large survey covering nearly 100,000 people over 30 years. In the United States, there are 3.5 million asthmatics and a new patient is born every 10 minutes.

Women more at risk

The possible link between asthma and lung cancer has already been the subject of various scientific research. However, the results, which were sometimes contradictory, did not provide a definitive answer. Can the broader survey of the International Cancer Research Center (CIRC / IARC) of Lyon make it clearer?

A mechanism still unknown

Prof. Boffetta and his colleagues have compiled Swedish national registers, focusing on people who have been hospitalized and diagnosed with asthma during the last 30 years. Only those without lung cancer one year after discharge from hospital were included in the survey. This precaution has been taken "to avoid any risk of reversed causation, that is, an asthmatic symptomatology due in fact to lung cancer," says Prof. Boffetta. Were followed for an average of eight and a half years.

3.5 million asthmatics in the United States

This prospective study (looking to the future of asthmatic patients) differs from previous studies, based on the medical history of patients with lung cancers.

Requiring larger numbers, prospective studies are thus more reliable. By its magnitude and the methodology employed, the IARC study could end the debate.

At the end of the study carried out the IARC in Lyon, the University of Uppsala and the Karolinska Institute in Stockholm, researchers identified 713 cases of lung cancer. This figure represents a much greater risk than that of the general population. The average risk exceeded 58%. Women with asthma appear to be more severely affected than men: 78% against 51%.

The risk of lung cancer is even greater in people with multiple illnesses, especially those hospitalized for reasons other than their asthma. Risk elevation concerns in particular certain types of lung cancer: squamous cell carcinoma and small cell carcinoma. The percentage of adenocarcinomas has remained fairly close to that of the general population.

The authors acknowledge that they do not really know whether asthma as such is the cause of increased risk. Very cautious about the interpretation of their results, they struggle to explain the link between these two diseases. At most, some hypotheses can be put forward

"Follow-up of young asthma patients over a longer period of time should provide important information on the possible carcinogenic process of asthma on the lung."

Asthma affects nearly 10% of individuals in Western countries and affects 150 million people worldwide. In the United States, there are 3.5 million asthmatics and every 10 minutes a future small patient is born. Asthma is the most common chronic disease in pediatrics. This situation is not peculiar to the Hexagon. Over the past 20 years, all European countries have seen an increase in the number of cases of asthma and allergic diseases.

* Eur respir J 2002; 19: 127-133