Exploring the causes of cutaneous B-cell lymphoma: we should learn from the Lyme disease experience

Epidemiological studies rely on the uneven distribution of disease within and between populations and represent a simple but efficient way of studying disease causation. The incidence of non-Hodgkin's lymphomas (NHLs) has increased dramatically over the past few decades and the epidemic calls for epidemiological studies. The study of Munksgaard and colleagues, in this issue of Dermatology, is a good example of an epidemiological study based on the so-called ecological correlation. It focuses on cutaneous B-cell lymphoma (CBCL) and fails to document a correlation between CBCL incidence and Lyme disease as a surrogate indicator for the exposure to tick bites. Although ecological studies neither inform about the time relationship between exposure and disease nor usually allow control for confounding variables, they can provide important information that would guide the direction of further research. There is a number of analytical studies focusing on risk factors for NHLs. One drawback of these studies is that they consider NHLs as a single category. One merit of the paper of Munksgaard et al. is that it focused on a rather specific disease, i.e. CBCL.