Author: Ivan Bowley, 12KBW
This post by Ivan Bowley comments on the recent decision of the High Court in McNally v Gentoo Group Ltd [2026] EWHC 750 (KB) in which the Claimant succeeded in his claim for damages in respect of mesothelioma.
The Claimant, aged 66 at the date of trial, was exposed to asbestos over many years during his employment with Sunderland Council as a painter and decorator. The Claimant developed a pleural tumour which resulted in the onset of breathlessness in July 2023. A CT scan suggested mesothelioma, but the immunohistochemical results from cytology and biopsy undertaken at the Claimant’s treating hospital were equivocal, if anything slightly favouring lung cancer. Molecular testing undertaken to inform treatment options did not identify mutations predictive of a response to treatment for lung cancer and following further imaging the MDT decided to treat the tumour as a mesothelioma.
Judgment on breach was entered in January 2025 and shortly before trial damages were agreed. The only live issue at trial was diagnosis: whether the Claimant was suffering from mesothelioma due to asbestos exposure, or lung cancer.
The Claimant called evidence from Dr Rudd (chest physician) and Professor Nicholson (histopathologist). The Defendant called evidence from Dr Moore-Gillon (chest physician) and Professor Attanoos (histopathologist).
It is uncontroversial that a diagnosis of mesothelioma should take account of the radiology and the clinical setting as well as histopathology. However, a very small proportion of peripheral pleural tumours showing the radiological appearance of mesothelioma are in fact lung cancers (figures given at trial indicate between 0.3% and 6%). These tumours cannot be distinguished from mesothelioma by imaging alone.
The Claimant also responded well to immunotherapy. Again, this was not diagnostic as he had a 95% positive result for PDL1 cells so lung cancer would probably have responded in the same way in any event.
This left the histopathology. There is no single specific immunohistochemical marker for mesothelioma. The current ‘Guidelines for Pathologic Diagnosis of Mesothelioma’, published in 2024, and contributed to by both Professors Nicholson and Attanoos, recommend the use of a panel of markers with specific requirements for differential diagnosis. The tissue samples examined at the Claimant’s treating hospital did not meet the necessary criteria. Further immunohistochemical testing was carried out at the Brompton Hospital. Reporting on those results Professor Nicholson initially concluded that the diagnosis was probably lung cancer rather than mesothelioma. However, he recommended further molecular testing (next generation gene sequencing) which is not widely available but is undertaken at the Royal Marsden Hospital. In Professor Nicholson’s opinion the results of this further molecular testing tipped the balance in favour of mesothelioma.
Professor Attanoos also reviewed the tissue samples and requested further immunohistochemical analysis with a broader panel of markers. This extended panel included Claudin-4 which was positive in this case. Claudin-4 has reported specificity of over 99% for lung cancer. The Guidelines state that Claudin-4 is positive in 99% of lung adenocarcinomas but for mesothelioma is “virtually always negative”. Professor Attanoos therefore maintained that the correct diagnosis was lung cancer and not mesothelioma.
Professor Attanoos also argued that the molecular testing undertaken at the Royal Marsden was not a sufficiently validated method for differential diagnosis between mesothelioma and lung cancer and should not be used to overturn the immunohistochemistry and in particular the result of the Claudin-4 test.
The Judge’s findings in this complex case largely turned on his assessment of the evidence of the histopathologists. He described the evidence of Professor Nicholson as “refreshingly candid, thoughtful, and considered in its delivery.” Professor Nicholson had changed his mind about the diagnosis but was able to justify that change of opinion on the basis of the molecular testing. Conversely the Judge was not satisfied that Professor Attanoos had engaged sufficiently with the results of the molecular testing. Notwithstanding the result of the Claudin-4 test, the Judge therefore concluded that Mr McNally was “one of those very rare individuals who come within a very small percentage of cases where the positive result is not indicative of lung cancer.”
Footnote: Because of the equivocal diagnosis in this case causation of lung cancer was considered at an early stage, but it was decided that the claim should proceed on the basis of mesothelioma alone.
