A rare medical case has been reported in which a fetus developed cancer in the uterus and the tumor cells spread to her twin sister before birth. The transmission occurred in utero, according to the report.
The case is described as very rare, highlighting an unusual pathway for cancer spread between twins. The source provides limited details about the cancer type or the twins' subsequent condition, but the finding underscores how cancer cells can sometimes cross from one fetus to another during pregnancy.