Two children in Japan 'caught' cancer from their mothers, in a rare medical phenomenon, new case reports. 

They likely inhaled cancer cells from their mothers, each of whom unwittingly had cervical cancer. 

A baby has to pass through the mother's cervix during childbirth and doctors think that cancer cells find their way into the amniotic fluid surrounding the infant, who then inhales the cells as they open their mouth to take their first breath and cry. 

In rare cases, a baby can inhale cervical cancer cells that have drifted into amniotic fluid in the birth canal, causing them to develop lung cancer years later 

Plus, even if a woman gets pregnant while she has cancer or is diagnosed with cancer while pregnant, it's very rare for the cancer to affect her developing baby. 

So even if tumor cells from the cervix wind up in the amniotic fluid, there isn't much opportunity for them to be transmitted to the baby. 

The first child was diagnosed with lung cancer about 23 months after his birth, when he developed a persistent cough. 

But before then, scientists sequenced genes in the mother's and child's tumors, and saw a clear link between them, suggesting that the cancer had probably been transmitted from mother to baby.  

He showed no signs of illness for another four years, but at age six, developed chest pain and was diagnosed with lung cancer as well.