Smoking is the most important risk factor for developing a primary tumor unknown (PTO). Alcohol consumption, diabetes and a family history of cancer are also associated with the risk of PTO, but to a lesser extent. This is the conclusion of Dr. Karlijn Hermans (Maastricht University) in her dissertation based on data from the Dutch Cancer Registry and the Dutch Cohort Study on nutrition and cancer. Hermans investigated the relationship between lifestyle habits and the risk of a PTO.
Relationship lifestyle habits and PTO
Hermans investigated the influence of alcohol consumption, cigarette smoking, physical activity, fruit and vegetable intake, meat intake, body type, diabetes and a family history of cancer in relation to the risk of developing a PTO. She also examined the influence of lifestyle in general by looking at whether adherence to lifestyle recommendations for cancer prevention (as defined by the World Cancer Research Fund and the American Institute for Cancer Research) has an impact on the risk of developing PTO, but after multivariable analysis, no statistically significant relationship emerged in the cohort. Hermans also conducted a literature study into risk factors for PTO and compared these findings with the observed risk factors within the Dutch Cohort Study into Diet and Cancer (NLCS).
The NLCS is a prospective cohort, with a study population of 120,852 participants (62,573 females and 58,279 males) who were between the ages of 55-69 in 1986. The participants completed a questionnaire in 1986 about dietary habits and other risk factors for cancer. The cohort participants were followed for 20 years (until December 2006). Hermans linked data from the entire cohort to the Netherlands Cancer Registry (NKR) to identify PTO cases in the cohort.
Smoking and alcohol risk factors in cohort
Based on the data from the NKR and NLCS, Hermans concludes that the use of alcohol and smoking are risk factors for getting a PTO. Hermans found a dose-response relationship for alcohol consumption. The more alcohol a person consumes, the higher the risk of a PTO. This is especially true for the men in the cohort. Hermans also found a dose-response relationship in smoking behaviour: the more and the longer someone smokes, the higher the risk of a PTO. Participants who were diagnosed with type 2 diabetes at age 50 or later were also found to have a higher risk of PTO. This was especially the case for women.
Intake of specific beef and processed meat also appears to be a risk factor for PTO within the cohort, especially for women. Consumption of red meat in general, poultry and fish was not related to the risk of PTO. A family history of cancer was not an independent risk factor in the cohort, although Hermans saw a moderately increased risk of PTO in participants who had a brother or sister with cancer. There was no association between body type or physical activity and the risk of PTO. Vegetable and fruit intake also appeared to have no relationship with the risk of PTO.
Smoking established risk factor
Hermans compared the risk factors within the NLCS with the risk factors that emerged from other epidemiological studies of PTO risk factors. Smoking appears to be an established risk factor for PTO. Alcohol consumption, diabetes and a family history are less associated with the risk of PTO. There was no convincing association between body type, dietary intake (animal or vegetable), immune disorders, general lifestyle, physical activity or socioeconomic status and the risk of PTO.
More information
Karlijn Hermans defended her thesis ‘Cancer of Unknown Primary, uncovering risk factors associated with a neglected disease’ on 15 November. Co-promoters were Dr. Leo Schouten (Maastricht University) and Dr. Caroline Loef (IKNL).