A new study, published online last week by the journal Cancer, found that patients with ME/CFS (myalgic encephalomyelitis aka chronic fatigue syndrome) have an increased risk of developing certain types of cancer later in life – most notably non-Hodgkin lymphoma.
Study Design and Results
Because ME/CFS is thought to be associated with immune abnormalities or infection and cancer can arise from similar conditions, associations between the two were examined in a population-based case-control study among the elderly in the U.S.
Using the Medicare database, researchers identified 1.2 million cancer cases and 100,000 population-based controls between the ages of 66 and 99. They evaluated the risk for a wide range of cancer types for those patients who had been diagnosed with ME/CFS.
The association between ME/CFS and cancer was calculated using odds ratios. An odds ratio (OR) of 1.0 indicates no difference in average risk between ME/CFS and non-ME/CFS populations; an OR higher than 1.0 signifies greater average risk for people with ME/CFS; and an OR below 1.0 means a lower average risk for people with ME/CFS. For example, an OR of 1.88 would indicate an 88 percent greater average risk for ME/CFS patients.
Although several types of cancer showed an OR above 1.0, only non-Hodgkin lymphoma (NHL) withstood multiple comparison adjustment. ME/CFS was associated with an increased risk of non-Hodgkin lymphoma with an OR of 1.29. When the NHL was broken down into subtypes, the ORs were as follows:
Large B-cell lymphoma – OR = 1.34
Marginal zone lymphoma – OR = 1.88
B-cell NHL not otherwise specified – OR = 1.51
The scientists concluded, “Chronic immune activation or an infection associated with CFS may play a role in explaining the increased risk of non-Hodgkin lymphoma.”
These are scary, although not unexpected, findings. A number of ME/CFS experts like Daniel L. Peterson, MD have long been saying that they see an increased prevalence of cancer – particularly lymphoma – among ME/CFS patients. And the recent clinical trial in which ME/CFS patients who were given the chemotherapy drug Rituxan (rituximab) showed significant improvement certainly adds fuel to the fire.
Before we rush to hit the panic button, though, there are a couple of things we should keep in mind:
ME/CFS is thought to have multiple subsets. We don't know whether all ME/CFS patients are at a higher risk for cancer or if the increased risk only applies to certain subsets of people with ME/CFS.
A study based solely on mining a huge database like Medicare's is subject to many unknown variables. For example, a patient was considered to have ME/CFS if their doctor used the ICD-9 code for CFS. Yet we have no way of knowing what, if any, diagnostic criteria was used. Some doctors may have even used the CFS code when their patient was fatigued and they couldn't figure out what was causing it.