The review of more than 2,000 cases handled by Dr Carol Starkie, consultant pathologist at Selly Oak Hospital, Birmingham, can only be done by a handful of experts and is expected to take several months.
A full clinical review of all 42 wrongly identified cases is to be undertaken by a team of surgeons, radiologists and cancer specialists. But the retesting of patients from as far back as 1985 could lead to long delays before the results are known.
South Birmingham Health Authority commissioned one pathologist to examine the 473 samples taken in the previous 12 months once the inquiry was launched in May. By the middle of this week, he had completed the review of just 192 samples.
Discussions are being held with other hospitals but it appears unlikely that they will be able to test more than 500 samples a month without disruption to testing of new patients.
'There are major logistical problems in undertaking the re-examination of just over 2,000 tissue samples,' the authority admitted. The investigation at the Royal Orthopaedic Hospital was ordered after two patients, Matthew Guest, aged 9, and Debbie Leary, 14, were wrongly diagnosed and received chemotherapy treatment for cancer they did not have.
Tony Hall, solicitor for the Guest family, said: 'I have seen Matthew and he looks fine but I have seen no medical report which says he will not suffer long-term side effects from the treatment he received.'
Colin Lovatt, of Tunstall, near Stoke-on-Trent, said last night that doctors had made two mistakes when they diagnosed his daughter Michelle as suffering from cancer. He said Ms Lovatt, now 20, was told she had a malignant tumour in her right leg and was given chemotherapy.
Days later, they decided the tumour was benign and surgeons removed part of her leg bone. Three weeks later, Ms Lovatt was called back to the Royal Orthopaedic Hospital when doctors decided after a fresh examination of tests that the tumour was malignant. She went through a second spell of more powerful chemotherapy before the treatment was halted when it was decided again that the tumour was benign.
Her father said: 'It is bad enough for a mistake to be made once, but twice is just unbelievable. Michelle has been through hell twice over. We are just appalled.'