Q & A: Making sense of new research on possible link between phototherapy for newborn jaundice and cancer
May 23, 2016
Pediatric oncologist and neonatologist discuss new big-data studies
Two new studies published in the journal Pediatrics analyze large datasets to see if there is a link between phototherapy (light therapy) for newborn jaundice and pediatric cancer. One study found a statistically significant association; the other did not. A companion editorial explores the implications of the studies. Lindsay Frazier, MD, a pediatric oncologist at Dana-Farber/Boston Children’s Cancer and Blood Disorders Center and lead author of the editorial, and Anne Hansen, MD, MPH, a neonatologist and medical director of the Neonatal Intensive Care Unit at Boston Children’s Hospital, answer questions about the new research and its implications.
Q. What is newborn jaundice?
Anne Hansen, MD: Jaundice is a yellow color that can be seen in the eyes and skin due to elevated levels of a substance called bilirubin. Bilirubin is released as part of the normal life cycle of the red blood cell. Due to immature functioning of newborns, it is common for babies to have mild jaundice between about two days and two weeks after birth. In some circumstances, if untreated, infants’ bilirubin levels can get high enough to cause hearing loss and even brain injury.
Q. What is light therapy, and how is it used to treat newborn jaundice?
Anne Hansen, MD: Light therapy, also called phototherapy, is a very simple treatment in which a specific frequency of light is shined on a baby’s skin. The light converts the bilirubin in the skin to a related substance that is easier for the newborn to pass from the body. We know that light therapy is effective in lowering bilirubin levels and avoiding hearing loss and brain injury. In the United States, about 250,000 babies receive light therapy every year.
Q. What, if any, association between phototherapy and childhood cancer did the two new studies find?
Lindsay Frazier, MD: Two big studies led by researchers at the University of California San Francisco looked at the issue. The first, which analyzed administrative records of five million children born in California hospitals between 1998 and 2007, found a statistically significant association between phototherapy and two types of pediatric cancers – acute myeloid leukemia (AML) and kidney cancer. The second study examined medical records of 500,000 babies born in Kaiser Permanente Northern California hospitals between 1995 and 2011. It found no statistically significant association with childhood cancer, after adjusting for other possible risk factors.
Q. Why are big-data studies like this important to childhood cancer research?
Lindsay Frazier, MD: What causes childhood cancer remains one of the great unsolved questions in medicine. Unlike adult cancers in which we can point to many preventable causes of cancer, like smoking and obesity, we still understand virtually nothing about what elements, beside genetics, can cause a child to develop cancer. The main reason this has been such a vexing problem is that childhood cancer is very rare. For instance, with 225,000 new cases of lung cancer diagnosed annually in the United States, its association with smoking was relatively easy to establish. On the other hand, only 15,000 new cases of pediatric cancer – of all types – are diagnosed annually. This means that researchers who want to examine the relationship between an exposure, such as phototherapy, and childhood cancer must analyze large datasets in order to have enough cases to be statistically significant. The study of the etiology of pediatric cancer has been hampered by this fact. Large datasets, such as the ones analyzed in these California studies, present an opportunity to study an outcome as rare as pediatric cancer.
Q. What should clinicians and parents take away from these new research findings?
Lindsay Frazier, MD: Phototherapy has been perceived by most as causing minimal risk to the infant. Although these studies are inconclusive and do not prove a relationship between phototherapy and cancer, they should give us pause. One of the most striking findings was the authors’ data on the dramatic increase in the number of children who are receiving phototherapy, at least in the Kaiser Permanente system, in part, they suggest, because of the availability of units that can be used in the home. In 2011, 15.9 percent of the Kaiser infants received phototherapy, up from 2.7 percent in 1995. The risks associated with such a prevalent exposure require close scrutiny. If I were the one prescribing phototherapy today, I would want to be sure it was indicated.
Anne Hansen, MD: Although one Pediatrics study found a statistically significant correlation between phototherapy and cancer, that does not mean the light therapy caused the cancer. By contrast, it is well-established that severe jaundice can cause hearing loss and brain injury if left untreated. We also know that light therapy decreases bilirubin levels and prevents hearing loss and brain injury. So, we need to balance what we do with early stage data about correlations against known, substantial neurologic risk. That said, the new research is suggestive enough that clinicians should be mindful of the possible risk in cases in which mild jaundice is likely to resolve on its own. While we must always strive to understand the possible side effects of any our treatments, light treatment, overall, is safe and the benefits of offering it, when indicated, far outweigh the risks.