An elderly woman suffering inoperable lung cancer was left in "unbearable pain" due to inadequate treatment at a Scunthorpe hospital, an inquiry found.
Staff at Scunthorpe General "neglected to manage the pain" of the patient, identified only as Mrs N, the Health Service Ombudsman concluded.
Delays in her diagnosis over three months left Mrs N "greatly distressed".
Northern Lincolnshire and Goole Hospitals NHS Foundation Trust has apologised over the "tragic case".
The ombudsman said the case highlights the fact that the NHS is failing to treat elderly patients in England with care, dignity and respect.
It was one of 10 cases chosen for an in-depth review, which found people aged over 65 suffered unnecessary pain, neglect and distress.
Mrs N was provisionally diagnosed with lung cancer by her GP in October 2007, but this was not confirmed until January 2008.
Her daughter said due to the delay she was not given adequate pain relief and her family spent a "particularly distressing" Christmas watching her suffer while unable to help.
She said: "Our mother continued to suffer for too long."
When Mrs N was admitted to hospital in January 2008 saying she was in "unbearable pain", it was five days before she received adequate treatment.
On one occasion she asked for pain relief and was told she had already taken it, but a Macmillan Nurse later found that was not the case after checking the drugs chart.
Extra staff hired
She was not told about an earlier scan that showed the cancer had spread to her spine until March 2008, and died the following month aged 82.
Deputy Ombudsman Kathryn Hudson said: "What I think happened was that they forgot to consider Mrs N as a person.
"They pursued trying to get the diagnosis of cancer and the exact form of cancer and neglected to treat the fact that she was in very great pain and if they had done that her life might have been better while they were trying to sort things out."
Northern Lincolnshire and Goole Hospitals NHS Foundation Trust said systems have been reviewed, additional staff training in pain and symptom control brought in and an extra lung cancer nurse appointed.
The family was given £2,000 compensation.
A spokesman added: "This was a tragic case, and we would like to again offer our sincere apologies to the patient's family."