Tracey King (As Personal Representative of the Estate of Kevin King, Deceased) v South Tees NHS Hospital Foundation Trust

In a clinical-negligence claim involving statistical medical evidence, causation remains a question for determination on the balance of probabilities. Statistical evidence may be relied upon, but it must be assessed alongside evidence relating to the individual claimant. The court must not allow general probabilities to obscure relevant individual evidence. Medical literature may inform medical practice, but it should be approached cautiously when used to determine legal causation. Where expert evidence relies on a small or methodologically limited study, theoretical calculations, or unsupported assumptions about disease progression, the court may reject that evidence as an unsafe basis for inference.

The claimant, suing as personal representative of the estate of her deceased husband, brought a damages claim following the admitted failure to act on a chest X-ray indicating possible lung cancer. The issue was whether, had the breach not occurred, the deceased would probably have had clinically detectable N0 disease in May or June 2016.

The experts agreed that earlier diagnosis would have avoided death in February 2017, but disagreed whether the cancer would then have been localised N0 disease or locally advanced N2 disease. The court therefore had to evaluate statistical evidence, medical literature, clinical experience and the deceased’s subsequent disease progression.

1. Issue and applicable standard. The court had to determine, on the balance of probabilities, whether the deceased would have been clinically N0 in May or June 2016. Clinical staging based on scanning had to be distinguished from pathological staging based on later histological examination.
2. Statistical evidence. The evidence from the Oda and Goldstraw papers indicated a 68–75 per cent probability that a patient with a primary tumour of approximately 3 cm would be N0 clinically. In accordance with Wardlaw v Farrar [2004] EWCA Civ 1719, statistical evidence could be relied upon, but had to be weighed with evidence particular to the deceased. The court also approached the medical literature cautiously because it was generally published to inform medical practice rather than determine legal causation.
3. Survival evidence. The deceased’s eight-month survival period did not safely establish the stage of disease in June 2016. There were too many variables, including the uncertain effect of chemotherapy.
4. Wang paper and tumour-growth hypothesis. The Wang paper was not a sound basis for concluding that lymph nodes grew at the same rate as the primary tumour. It involved a small cohort, a short interscan period and uncertainties about the relevant tumour type. The proposed doubling-time calculations also depended on unproven assumptions and confused pathological with clinically detectable disease. The court rejected the resulting estimates.
5. Expert evidence and conclusion. The court preferred Dr Lester’s evidence. The later PET findings were not inconsistent with the deceased having been N0 in June 2016. On the clear balance of probabilities, he would have been in the majority of patients with a 3 cm primary tumour who were N0. Judgment was therefore entered for the claimant on the sole issue for determination.