“Scientists prove cancer can be passed on in the womb,” reported The Guardian today. The newspaper said that in the first proven case of cancer cells passing through the placenta, a mother had passed on leukaemia to her unborn child.
The case study behind the news stories is the first genetic evidence for mother-to-child transmission of leukaemia cells. As newspapers reported, infants’ immune systems usually destroy potentially malignant cells passing through the placenta from their mother. But in this case, the child also carried a genetic mutation making the cancer cells unrecognisable to the immune system.
It is important for mothers to know that this is extremely rare and only a handful of cases have been recorded. Healthy pregnant women should not be worried. The chances of a woman with cancer passing on the disease to her child are also low.
Where did the story come from?
The study was carried out by Drs Takeshi Isoda, Mel Greaves, Shuki Mizutani and colleagues from Tokyo Medical and Dental University, the Institute of Cancer Research in Surrey, the University of Southampton and other medical and academic institutions in Japan.
The research was funded by grants from the Ministry of Education, Science, Sports and Culture and the Ministry of Health, Labor and Welfare in Japan and from Leukaemia Research UK.
It was published in the peer-reviewed medical journal Proceedings of the National Academy of Sciences .
What kind of scientific study was this?
Researchers undertook this laboratory study of a single case of cancer in an infant that may have a maternal origin. They were looking for proof that it is possible for cancer to be transmitted from a mother to her child.
The study subjects were a 28-year-old Japanese mother with an uncomplicated pregnancy and birth, and her child. However, some weeks after the birth, the mother developed vaginal bleeding and other symptoms. She was diagnosed with acute lymphoblastic leukaemia (ALL) and eventually died.
ALL is a cancer of the white blood cells (B and/or T cells) and is the most common form of leukaemia in young children, but can appear in adults too. There are different types of ALL and the mother’s cancer was classed as cancer of the precursor-B cells (the earliest cells in the development of B cells). She also had a gene mutation in a gene called BCR-ABL1, which is known to be involved in the malignant transformation of these types of cells.
The BCR-ABL1 mutation is common in leukaemia and occurs when two chromosomes (9 and 22) break and refuse to form hybrids. The mutation happens in different places each time and the exact genetic sequence of the mutation was key to understanding whether the cancer was the same in the mother and child.
The child initially had normal growth and development after she was born. This changed when she was 11 months old, when she developed unusual symptoms (a tumour in her cheek and fluid in her lungs), prompting further investigation. Tests revealed that the child had not inherited the BCR-ABL1 mutation from the mother (the child’s bone marrow cells did not have this gene abnormality), but the child’s cancerous cells did carry this mutation, suggesting that they were passed through the placenta.
The child received chemotherapy for her cancer and at the time of publication was reported to have had a good response and to have been in remission for 18 months since her diagnosis.
The child’s cancer cells were also missing some genes related to immune system function. Specifically, the child’s cancer was missing some genes that control the expression of molecules as part of the "major histocompatibility locus" (a large genomic region or gene family found in most vertebrates). In the absence of these cells, the infant’s immune system would not have recognised that the cancerous cells were foreign.
What interpretations did the researchers draw from these results?
The researchers say that their findings “unambiguously mark the infant cancer as of maternal origin” but they also note that the rarity of such cases is evidence of the effectiveness of the placental barrier and immunity.
What does the NHS Knowledge Service make of this study?
This case study is the first genetic evidence that it is possible for cancer to pass from a mother to child through the placenta. The scientists say that such spread may in fact happen more often but the infant’s immune system usually destroys potentially malignant cells passing through the placenta from the mother. In this case, the child’s cancer also had a mutation that meant it evaded detection by the immune system.
The transmission of cancer cells is extremely rare and healthy pregnant women should not be worried about this. The chances of a woman with cancer passing on the disease to her child are also low.