Cancer proven to pass from mother to baby

A rare case of a mother and her infant developing the exact same cancer has allowed an international team of researchers from the Institute of Cancer Research (ICR), to solve a puzzle that has perplexed scientists and clinicians for a century. The scientists, with funding from Leukaemia Research, investigated a situation in which leukaemic cells appeared to have defied accepted theories of biology and spread through the womb from a Japanese woman to her daughter.

Approximately 30 previously-known cases of a mother and infant appearing to share the same cancer had already raised suspicions that such spread was possible. However, there was no genetic evidence to support this theory, and investigators did not know how it could occur as the baby's immune system should have recognised and destroyed any invasive cancer cells that were of maternal, and therefore foreign, origin. In a study, published in the 12th October online edition of PNAS (10.1073/pnas.0904658106), the scientists used advanced genetic fingerprinting to prove for the first time that the infant's leukaemic cells were unquestionably of maternal origin.

The researchers found that both patients' leukaemic cells carried the identical mutated cancer gene, Bcr-Abl1, but the infant had not inherited this gene. This meant that the child could not have developed this type of leukaemia in isolation. To investigate how the cells could have crossed the placental barrier and survived in the offspring, the scientists looked for evidence of some form of immunological acceptance or tolerance of the foreign cells by the foetus. They examined the genes of the cancer cells in the infant and found some DNA missing in the region that controls expression of the major histocompatibility locus. This was significant because HLA molecules primarily distinguish one individual, and his or her cells, from another, so the absence of these molecules on the cancer cells meant that the infant's immune system would not have recognised that they were foreign.

It appears that in this and, the scientists presume, other cases, the maternal cancer cells did cross the placenta into the developing foetus and succeeded in implanting because they were invisible to the immune system. Dr David Grant, Scientific Director at Leukaemia Research, commented: "the important message from this fascinating piece of research is that leukaemia cells can be destroyed by the immune system. Harnessing the power of the immune system to first cure and then protect patients from leukaemia is one of our priority areas of research."

According to Professor Peter Johnson, Cancer Research UK's Chief Clinician, this finding provides further evidence that cancers are generated more often than first thought. A large part of cancer research is on cancer immunity; scientists have known for quite some time that people with deficient immune systems, perhaps because of HIV or immunosuppression after organ transplants, are much more prone to certain types of cancer. The real challenge for researchers now is to work out how to invigorate the immune system so it recognises cancer cells.

Alice Rossiter
Cancer Drug News Editor