Ron Badham, of West Bromwich, says he was robbed of 10 more years with his wife Mary because of the mistakes.
The 79-year-old has now received a substantial compensation settlement, after Sandwell and West Midlands NHS Trust, admitted its failure to carry out a colonoscopy fell below a reasonable standard, and therefore admitted breach of duty.
When his wife of 45 years Mary died from bowel cancer in 2014, Ron was left with questions over why it was not identified at Sandwell Hospital in 2009.
Mrs Badham had visited her GP with symptoms of bowel cancer, then aged 65, and been referred to the hospital.
However, she was diagnosed, without a colonoscopy, as suffering from Irritable Bowel Syndrome and sent home with tablets.
The case was made against the Trust through clinical negligence specialists Hudgell Solicitors.
An independent expert, who was instructed by the firm to study Mrs Badham's medical reports, concluded she would have had a good chance of being treated, and living for at least another 10 years, if the bowel cancer had been spotted in 2009.
Instead, because it went undiagnosed for two further years, it had spread to her lymph nodes by the time it was found.
Mr Badham, a retired accountant, said: "This has been very hard for myself, our two sons, and our grandchildren.
"The circumstances of the loss that are hard to accept – that she could have lived longer if they'd found the cancer when they should have done."
Housewife Mrs Badham had gone to see her GP because she was passing blood and suffering from diarrhoea. She was referred to a specialist who diagnosed her with IBS.
It was only after she was invited to Bowel Cancer Screening in 2011, she found it was terminal cancer.
Caroline Murgatroyd, a clinical negligence specialist at Hudgell Solicitors, said: "We hope this settlement provides some comfort, and it helps raise awareness to demand tests, or seek second opinions."
Rachel Barlow, Trust chief operating Officer said: "We would like to pass on our deepest sympathies to Mary's family."