Cardiff sisters discover they are identical twins after cancer diagnosis
BBC World
February 24, 2026
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Caitlin Leggett, a 23-year-old from Cardiff diagnosed with acute myeloid leukaemia (AML), had hoped her identical twin sister Grace could donate stem cells to aid her recovery. However, doctors revealed the sisters were not only twins but actually identical, complicating Caitlin's treatment plans. Initially thought to be fraternal twins due to being in separate amniotic sacs, they discovered their DNA was near-identical, making Grace an unsuitable donor for a stem cell transplant. This unexpected revelation forced the cancellation of her planned August transplant and led to Caitlin joining a clinical trial in Manchester.
The sisters grew up sharing close bonds and hobbies, both attending the University of Bristol where they lived together. Caitlin studied psychology while Grace pursued neuroscience. Their identical nature was uncovered during medical testing for Caitlin's leukaemia diagnosis, which initially seemed promising as Grace had registered as a potential donor with DKMS years prior. However, upon realizing their identical status, doctors explained that the transplant would not work due to the high risk of complications.
Caitlin's journey took an unexpected turn after her rash led to a blood test revealing leukaemia. Diagnosed at the University Hospital of Wales, she faced an aggressive cancer treatment plan including chemotherapy and a stem cell transplant. Her initial hope for recovery hinged on Grace’s donation, but the twins' identical DNA made this impossible. Caitlin later joined a clinical trial in Manchester after her leukaemia spread to her skin.
The sisters’ story highlights the importance of understanding twin biology and the impact of such discoveries on medical treatments. Their case underscores the challenges faced by patients needing stem cell donations and the emotional toll on families navigating unexpected medical realities. The situation also serves as a reminder of the critical need for more people to register as potential donors, emphasizing how one person’s donation can save lives.
Caitlin and Grace are now advocates for increasing awareness about leukaemia and stem cell donations. Their experience not only sheds light on the complexities of twin relationships but also raises global attention to the importance of supporting those in need of life-saving transplants.
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Originally published on BBC World on 2/24/2026