The Prime Minister and Health Secretary have been given copies of the long-awaited report into serious failings at Mid Staffordshire NHS Foundation Trust.
Members of the Cabinet have discussed the report but did not review its contents because most have not yet seen it.
The spokesman told a regular Westminster media briefing: "The point the Secretary of State for Health and the Prime Minister were making in Cabinet was around the seriousness of the issue.
"The first Francis report into care standards at the trust highlighted what can only be described as completely unacceptable failure in care standards - failure which caused appalling distress to patients and their families.
"Given the scale of the failings that the original report uncovered, it is the Government's very clear view that it is important to get to the bottom of why these failings were undetected for so long. That's why it was right to set up the public inquiry focusing on the commissioning and regulatory regime, and why these failings were undetected."
The spokesman said that Mr Cameron had met representatives of victims' families in opposition and met them again at Downing Street on Monday.
"He would want his response to the inquiry to be fully informed by those who suffered so much," he said.
The report will be laid before Parliament on Wednesday and Mr Cameron will deliver a statement to the House following Prime Minister's Questions. It is understood that inquiry chair Robert Francis QC will recommend wide-ranging reforms of the NHS.
NHS Confederation chief executive Mike Farrar predicted that the release of the report would be "one of the darkest days" in the history of the NHS and acknowledged that changes were needed to make patient feedback easier and give the public a clearer picture of how local services were performing.