Fewer breast cancer patients received treatment within waiting time targets, according to the latest NHS statistics.
Mr Kerr said he would monitor the performance of all health boards
Health Minister Andy Kerr had pledged that by the end of last year all cancer patients who had an urgent referral would be treated within two months.
The figures revealed that some cancers were being treated quicker but Mr Kerr said that progress was not fast enough.
However, the figure for breast cancer went down from 86% to 81% during the last quarter of 2005.
"Today's figures show we are heading in the right direction with cancer types like colorectal, ovarian, lung and lymphoma, and that is good news for patients suffering from these dreadful diseases," he said.
"We have made significant funds available to boards to help them cut cancer waiting times.
"Nevertheless, this is an extremely challenging target and progress in some areas is not as good as I would have hoped."
He added that waiting times must be reduced and called on health boards to act.
Mr Kerr said he would closely monitor how each board performed.
The latest figures, covering the third quarter of last year, showed that the number of skin cancer patients treated within the target time remained static at 86%.
Lung cancer treatment times improved from 70% to 77%, ovarian cancer from 86% to 92%, colorectal cancer from 56% to 67%, and lymphoma from 58% to 64%.
Shona Robison MSP, the SNP health spokesperson, said: "This is not about missing NHS targets, it's about failing to provide an adequate standard of care to those individuals in most need, and that's why we need an action plan now setting out exactly how we improve the service.
"In addition, the report underlines the postcode lottery of cancer services in the NHS.
"All cancer patients deserve the best treatment possible, and so large variations in the standard of care administered are simply unacceptable."