A mother with leukaemia says she feels "distraught" and "helpless" after her sister, a perfect match as a stem cell donor, was refused a visa to enter the UK.
Nigerian-born May Brown, 23, was diagnosed with cancer last year.
After an "extensive search" - confirmed by King's College Hospital - she discovered her Nigeria-based sister was the only available 10 out of 10 match.
Ms Brown lives in Dorset with her two-year-old daughter, Selina. Her sister Martha, a schoolteacher, has two children and "no desire" to relocate to the UK, Ms Brown says.
The rejection means Ms Brown must plead with the Home Office "to help save my life", she says.
According to Ms Brown, the Home Office said it was "not satisfied" that her sister had the funds to cover the costs of the trip or that visit was genuine.
"I was elated when I received the news Martha was a 10 out of 10 match," Ms Brown said.
"But when I received notification her visa was rejected I felt distraught and helpless. My two-year-old daughter Selina needs me. She needs me to be back home with her, looking after her."
She said she is begging for the Home Office to review their decision.
"To know my life isn't important to those who have the power to help me is deeply upsetting," she said.
A petition has been launched by the blood cancer charity African Caribbean Leukaemia Trust (ACLT) and signed by more than 1,500 people asking for the decision to be reversed by the Home Office.
A Home Office spokeswoman said they don't comment on individual cases but added: "We are sensitive to cases with compassionate circumstances but all visa applications must be assessed against the immigration rules.
"The onus is on the individual to provide the necessary supporting evidence to prove they meet the requirements."