Cause and effect

New Zealand has the highest rates of bowel cancer in the world. Fortunately, the University of Otago is at the forefront of cancer research and new findings to bring these figures down.

The Hugh Adam Cancer Epidemiology Unit has been studying the causes of cancer and the effectiveness of cancer screening programmes for the past 25 years.

Director Associate Professor Brian Cox's team's current work has shown that most colorectal cancer in New Zealand is caused by an unknown exposure that occurs before a person's 25th birthday. The unit is now seeking funding to try to identify this unknown exposure, studying both colorectal cancer and colorectal polyps.

“The cellular mechanism by which an exposure causes cancer is usually worked out in a laboratory later,” says Cox.

Recent research by the unit has suggested that diet in childhood, particularly drinking milk, might offer some protection against colorectal cancer in later life. The result follows five years of study, interviewing more than a thousand people, with and without cancer, on their lifestyle, living environment and habits to find indications of what might have triggered the cancers.

“Wherever there are cells, there's always potential for them to become malignant. Some organs are far more prone to cellular aberration than others,” says Cox. “Most cancers grow in a very insidious form without symptoms for many, many years, often decades, prior to presenting with symptoms.”

When the disease eventually presents itself, it often leaves little or no trace of what caused it, so a productive line of enquiry is to profile the sufferers to find common threads that might lead to causes.
One of the unit's earlier studies ruled out any link between prostate cancer and vasectomies, much to the relief of the world's family planning agencies. That study was prompted by New Zealand having the world's highest prevalence of vasectomies.

“We try to capitalise on features of New Zealand that enable us to answer specific questions that have arisen in the international literature or that we think of ourselves,” says Cox.

Hence, the research into colorectal cancer which, in its early phases, identified that people born before about 1943 appeared to have twice the risk of developing the disease than younger generations.

“Cancer rates and the risk of cancer change over time,” says Cox.

“One of the tasks we have is to keep an eye on what is happening with various cancer rates. When changes occur, they don't happen quickly. You sometimes have to look over 30 years to see the changes occurring in the population.”

With the latest information on colorectal cancer narrowing the focus in the search for a cause, the unit is also investigating which screening tests would produce the greatest reduction in incidence and mortality in New Zealand.

A Health Research Council grant will allow the unit to compare two tests.

The first test is a two-yearly faecal occult blood test for people between 50 and 70, and the second is a one-off flexible sigmoidoscopy screening for those between 55 and 64 years old. The study will also assess what features of the two tests influence people's preference for testing and which groups prefer which test.

Cox says there are pluses for the sigmoidoscopy test, which is minimally invasive.

“As a single screening test in one's lifetime for colorectal cancer, one-off flexible sigmoidoscopy has an advantage as a screening test. It reduces both the incidence and mortality of the disease and only a few people would require long-term follow-up.”

The unit is also evaluating the costs associated with both types of screening and the expected improvement in outcomes. The collaborative study involves numerous investigators in New Zealand and overseas.
Other current research has shown that, despite efforts to prevent it, melanoma incidence and its thickness at diagnosis is increasing. This is a major problem in New Zealand as patients with thicker melanomas have poorer rates of survival.

The unit is now seeking funding to evaluate a new model for predicting people's risk of developing melanoma, so that it may be used in clinical practice.

“Dr Mary Jane Sneyd of the unit has successfully developed a method of predicting an individual's chance of developing melanoma in the five years from assessment,” says Cox.

“We intend to extend and develop this technique further so that the risk of developing 
certain melanoma subtypes can be calculated. In the future, this could also be applied to colorectal and other cancers.”

Other, earlier projects have involved collaborative investigations of cancer of the breast, lung, head and neck, and the unit has extensive experience in the evaluation and monitoring of screening programmes, including the national breast and cervical screening programmes.

The unit was heavily involved in the development of the New Zealand Cancer Control Strategy, and is represented in the International Cancer Screening Network and the International Lung Cancer Consortium.

Continuing international collaboration keeps Otago's contribution to cancer control to the fore, says Cox, but people are what matter.

“The whole thrust of our work is to try to establish what can be done before the diagnosis to prevent the cancer or make treatment easier and, therefore, decrease deaths from the disease and improve the quality of life for people.”