An independent inquiry is to be launched after the charity Mencap highlighted six deaths of people with learning disabilities in NHS care.
One of the cases was that of Emma, 26, a woman with a severe learning disability, who died in 2004.
Her mother Jane took her to the GP because she had not eaten for eight days. The doctor thought it was a virus, but Jane thought her daughter's condition was something more serious.
A month later, Emma had to be admitted to hospital where she was found to have a swelling in her groin.
She was distressed and in great pain, and she could not eat or take painkillers orally. Her family say the hospital staff found it hard to look after Emma, who could display challenging behaviour and struggle to express how she felt.
Emma was discharged because the hospital said they could do nothing more to help her.
But 11 days later, test results showed she had lymphoma - a cancer of the blood.
Her family were told that, with treatment, she had a 50:50 chance of survival.
But doctors decided not to treat her, saying she would not co-operate with her treatment, and she was sent home.
However she was admitted again five days later because she could not drink. But, according to Jane, Emma still received no treatment for two days and care only started when the family's solicitor complained to the hospital.
At this point, doctors said Emma only had a 10% chance of survival after treatment and that the only option for her was palliative care.
Jane says: "We had serious doubts about her care; the delays and the lack of understanding and the fact that they weren't listening to us.
"She wasn't given basic care. We had to feed her and wash her.
"Nobody talked to her about her care, although we tried to advise them what she needed."
She added: "I know cancer treatment is expensive, and I feel like Emma wasn't seen as an investment."
Emma was transferred to a hospice for the last month of her life. Her condition, and her ability to take in liquids, improved while she was there.
The family has submitted a complaint to the Healthcare Commission, who are currently investigating the case.
Jane said: "We were devastated by Emma's death, and we also have to deal with the process of making a complaint."