Certain types of cancer becoming more common, while rates of others decreasing

Cancers showing a decrease in incidence in both sexes include lung, stomach and colon cancers.

"There are a variety of factors that may explain these numbers," says study author Elizabeth Ward. "Cancer trends over time could reflect changes in exposure to risk factors such as sun or smoking, changes in how we classify cancer or the introduction of new screening or diagnostic tests." Ward notes that while the incidence of some cancers is climbing, overall cancer mortality rates have decreased since 1991 for both men and women.

"For some cancers, the reasons for their changing incidence rates are somewhat clear," says Ward, citing well-known connections between sun exposure and smoking, with skin and lung cancers, respectively. "In a complex environment that is constantly changing, understanding the factors influencing other cancers, such as non-Hodgkin lymphoma or testicular cancer, will continue to be a formidable challenge."

Source: Blackwell Publishing Ltd.