Acute lymphocytic leukemia (“ALL”), also known as acute lymphoblastic leukemia, is a cancer of the blood and bone marrow, predominantly seen in children between the ages of two and five. ALL is the most common type of childhood cancer in the U.S., comprising 26% of cancers in children 14 and younger. In 2016, there were an estimated 6,590 new cases of ALL in the U.S.
ALL is characterized by a rapid progression of white blood cell precursors, called lymphoblasts, that improperly divide and interrupt the production of healthy blood cells. ALL can cause critically low amounts of red blood cells, white blood cells, and platelets, known as anemia, neutropenia, and thrombocytopenia, respectively.
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A new study published in the journal Blood provided the first evidence that congenital cytomegalovirus (“CMV”) infection may be involved in the development of ALL. While the exact causes of ALL remain uncertain, cancers are broadly thought to arise as a result of errors in a cell’s DNA. Previous research has linked ALL onset to radiation therapy, but very little is known about the exact mechanisms. Researchers have believed for some time that infections also play a role in the development of childhood ALL, but until recently no specific pathogens have been implicated.
CMV is a common virus that infects one in every two people in many developed countries. Most CMV infections are “silent,” meaning most people who are infected with CMV exhibit no signs or symptoms, however, the infection can be serious in certain patient populations, including newborns when a mother is infected during pregnancy. While it has not yet been proven to cause cancer, some studies have suggested a link between CMV and medulloblastoma, glioblastoma multiforme, and breast cancer.
In the new study published in Blood, researchers found that children diagnosed with ALL were 3.71 times more likely to have detectable levels of CMV in their blood at birth. The results were most pronounced in Hispanic children with ALL, who were 5.90 times more likely to have CMV in their blood at birth. This is noteworthy because Hispanic children have the highest incidence of ALL. The researchers also found that CMV was present in the bone marrow of patients who were diagnosed with ALL, but rarely in those diagnosed with acute myeloid leukemia (“AML”), another type of blood cancer. Similarly, the team found no association between ALL and infection with Epstein-Barr virus (“EBV”), another herpesvirus, further suggesting that CMV may play a role in the development ALL.
The researchers hypothesized that congenital CMV infection may lead to ALL by damaging the host’s chromosomes. Chromosomes are made up of tightly packed DNA. Thus, damaging a chromosome could lead to deleted or rearranged pieces of DNA, which could in turn lead to cancer. The researchers also suggested that CMV may dysregulate the host’s immune system. Previous studies have suggested that the immune system responds differently to CMV than it does to other viruses. This altered response may play a role in the development of ALL, but so far there is no explicit evidence of this. Further research is needed to confirm the correlation between CMV infection and ALL, and to better understand CMV’s oncogenic potential.