Cancer passing from a pregnant mother to her baby is an extremely rare but scientifically documented phenomenon. Research studies, including a 2021 report published in JCO Global Oncology and a 2018 analysis in PMC, have confirmed cases where maternal cancer cells successfully crossed the placental barrier or were transmitted during childbirth. Genetic sequencing in these studies showed that tumors in infants were genetically identical to the mother’s cancers, providing clear evidence of direct transmission. Although it occurs in roughly one in 500,000 pregnancies, understanding this phenomenon is vital for managing maternal cancer safely during pregnancy and improving outcomes for both mother and child.
How cancer transmission occurs from mother to baby
Transmission from mother to baby can happen through two primary routes: in utero across the placenta or during vaginal delivery. The placenta, while acting as a protective barrier, occasionally allows rare maternal cancer cells to enter the fetal circulation, leading to transplacental metastasis. Cancer can also be transmitted during vaginal birth if the baby aspirates cells from the birth canal, especially in cases of cervical or other reproductive cancers. Arakawa et al. (2021) documented cases where cervical cancer cells were transmitted to infants’ lungs during delivery, confirmed through shared genetic markers between mother and child tumors.
Types of cancer involved
The most commonly reported maternal cancers that have been transmitted to the fetus include melanoma, leukemia, cervical cancer, breast cancer, and lung cancer. Melanoma and leukemia are particularly notable due to their ability to metastasize widely and cross the placental barrier. Placental and fetal metastases are extremely rare, occurring in about 26–30% of women with these cancers, making such cases exceptional but potentially severe. Breast cancer with placental metastasis has also been documented, though it remains uncommon and presents unique treatment challenges during pregnancy.
Challenges and clinical implications
Because maternal-to-fetal cancer transmission is so rare, there are no standardized screening or treatment protocols specifically addressing this risk. Diagnosis often occurs only after the infant exhibits symptoms, sometimes months or years after birth. Genetic sequencing is key in confirming transmission by matching maternal and infant tumor mutations. Cesarean delivery may reduce transmission risk in certain cancers like cervical cancer. Managing maternal cancer during pregnancy requires careful balancing of the mother’s treatment needs with fetal safety, with the timing of interventions often guided by gestational age.
Differing opinions and uncertainties
While maternal-to-child cancer transmission is scientifically validated, many experts consider it an exceptional anomaly unlikely to change standard treatment strategies. The maternal immune system and placental environment generally prevent cancer cell implantation in the fetus. Nonetheless, studying these rare cases provides insight into cancer biology, immune evasion, and placental permeability. Advances in molecular diagnostics may reveal more cases in the future, potentially reshaping our understanding of perinatal cancer transmission.