The breast oncology consultant covering Tayside used smaller doses of some drugs, with a report from Healthcare Improvement Scotland (HIS) confirming patients were not informed about this difference.
Chief Medical Officer Dr Catherine Calderwood and Chief Pharmaceutical Officer Dr Rose Marie Parr ordered HIS to carry out the work after concerns were raised “about variations in treatment compared with other health boards in Scotland”.
The report also warned of a possible “dysfunctional team environment” in NHS Tayside, with debate on the issue said to be “stifled”.
Other medical professionals within the board “expressed concern” about the lower dosage, the report said.
HIS stated: “Outwith scope of the review there appears to be a culture within the team where the multi-professional voice is not being heard.”
The Chief Medical Officer and Chief Pharmaceutical Officer stepped in after cancer specialists in NHS Tayside, NHS Grampian and NHS Highland - who are all part of the North of Scotland Cancer Network - could not agree on clinical management guidelines for breast cancer treatment.
For patients being treated with a FEC-T regimen of chemotherapy, oncologists in NHS Grampian and NHS Highland recommended doses of 100mg/m2 of two of the drugs, Epirubicin and docetaxel, while in Tayside the recommended dosage was 75mg/m2 of Epirubicin and 80mg/m2 of docetaxel.
“It appears that NHS Tayside patients are not informed of the difference in practice in relation to other NHS boards within the region and other parts of Scotland,” the HIS report said.
It noted the practice in NHS Tayside was “also at variance with the rest of NHS Scotland”.
The “NHS Tayside breast oncology consultant team confirmed that patients were not informed of dosage or variation in dosage during the consent process”, the report said.
Doctors there had argued their practice was “in the best interests of patients in NHS Tayside” - saying that when higher doses of the drugs had been used in 2014-15, 51 of 98 patients had needed to have their dosage reduced.
NHS Tayside has now confirmed it will be “adjusting its breast cancer chemotherapy dose regime to make sure patients throughout Scotland are offered the same”.
The health board has also written to all patients who received chemotherapy treatment from breast cancer after December 1 2016, offering them an appointment with an oncologist for “further discussion about their treatment”.
Acting medical director Professor Peter Stonebridge said: “We understand that the HIS report published today may cause patients some concern - and even distress - and we are very sorry for that.
“We have taken assurance from the expert panel who has said that the risk of any negative impact to patients arising from the change in chemotherapy was very small.
“However, patient safety is always our number one priority and that is why we have taken action to rapidly change our approach to breast cancer chemotherapy, ensuring it is in line with practice across the rest of Scotland.”
In a joint statement, Dr Calderwood and Dr Parr said: “It is important to stress that the risk of a negative impact on the health of anyone treated for breast cancer in NHS Tayside since 2016 is very small.
“However, patient safety is our number one priority and we therefore take the findings and recommendations of this report seriously.
“They will be immediately considered by both the Scottish Government and NHS Tayside.”
The HIS report comes in the wake of concerns over the financial performance of NHS Tayside - including a payment for six months notice to former chief executive Lesley McLay when her contract only included three months notice.
In May 2018, then-health secretary Shona Robison announced an independent inquiry into mental health services in the area.