Thursday, 30 May 2013

Delay in Diagnosing Cancer (3) - Diagnosis and Staging

In Part 2 I considered the first links in the chain of causation - establishing when the claimant would have been seen by a specialist and what investigations would have been carried out, but for the negligent failure to refer. The next step is for the claimant to prove, on the balance of probabilities, that such investigations would have resulted in diagnosis of cancer.

In order to prove whether the investigations which would or should have been performed would have led to diagnosis it is necessary to establish what the likely features or characteristics of the cancer would have been at the relevant time. In rare cases there is direct contemporary evidence - a scan which was misinterpreted for example. Far more commonly the court will be invited to make a finding as to the presence and features of the cancer at the time when investigations were not, but ought to have been performed, by inference. Evidence from which inferences may be made will usually include reported symptoms over time and, most importantly, the features of the cancer when diagnosis was actually made.

An expert oncologist or histopathologist will take the evidence of the cancer at diagnosis - its size, its stage, its grade etc. and calculate or make a judgment as to the corresponding characteristics at the earlier time when investigations ought to have been performed - this is called interpolation. The expert will rely on evidence of how such cancers typically behave over time. For example there is evidence of "doubling times" for breast cancer - the period over which the tumour will double in volume. The doubling time will depend on the precise category of the cancer and the age of the patient.

Even with cancers such as breast cancers where there are published studies of doubling times, the experts will only be able to give a range of sizes for the tumour at an earlier time. Nevertheless they may be able to establish that on the balance of probabilities the tumour would or should have been detected on a triple assessment at a breast clinic.

There are greater difficulties with less common cancers, where there is a lack of data as to doubling times. Sometimes experts will rely on evidence of doubling times for similar cancers but this may be controversial. In McGlone-v-Greater Glasgow Health Board the claimant's expert had used published studies to interpolate the size of the claimant's cervical tumour at the time when it was alleged diagnosis ought to have been made. The Court of Session, Outer House, rejected that evidence. First, it found that it was inappropriate to rely on published evidence of doubling times for metastatic lung tumours as indicative of the likely doubling time for a primary cervical tumour. Second, it noted the very wide range of doubling times and rejected the notion that the court should simply take the mean doubling time within that range.

The decision in McGlone indicates that the use of statistical evidence without more can lead to difficulties in proving causation. Furthermore that where there is an absence of data directly relevant to interpolation in respect of the particular cancer, then the claimant may face further difficulties. Nevertheless the Court recognised that statistical evidence might be probative of a range of tumour size.

Of course evidence of the growth rates of tumours is difficult to obtain - clinicians do not generally leave a tumour to grow simply to observe how it behaves! If the courts were unwilling to rely on any statistical evidence or to make findings by inference then most claims for delay in diagnosing cancer would fail. This is an area where direct evidence of the features of the cancer at the time of the alleged negligence will, by definition, almost always be absent.

Sometimes the expert evidence will conclude that whilst the tumour would not have been present at the time when investigations ought to have been performed, pre-cancerous changes would have been present and detected - such as ductal carcinoma in situ in the breast. However merely establishing that the cancer or other abnormalities would have been present does not of itself prove that diagnosis would have been made. There seems to be a "rule of thumb", for example, that a breast tumour less than 1cm diameter might well be missed even on a reasonable clinical examination of the breast. Other investigations for other cancers are far from guaranteed to lead to diagnosis even if the cancer can be proved to have been present at the relevant time.

If diagnosis would or should have been made then by similar process, proof will be required of the characteristics of the cancer. Generally the relevant features are the size of any tumour, the stage and/or grade, and the spread of the cancer to neighbouring or distant sites. However associated symptoms may also be relevant to the categorisation of some cancers - for example night sweats. There are different categorisations for different cancers. So, melanomas may be measured for their Breslow thickness, colorectal cancers may be given a Dukes stage etc. For prostate cancer the stage is a measure of the extent of growth or invasion and the Gleason grade is a measure of the activity or aggressiveness of the cancer. Many cancers are categorised by reference to a TNM staging - T for tumour, N for nodes and M for Metastases. So a breast cancer may be T1N0M0 meaning that there were no axillary nodes affected and no metastases. I find the Cancer Research UK website very useful for information about grading and staging. 

So proof that diagnosis would have been made on earlier referral depends on a combination of evidence of the characteristics of the cancer at the relevant time and the investigations which would or should have been performed. Would those investigations have resulted in diagnosis of that cancer? The characteristics of the cancer at such time are relevant both to the likelihood of diagnosis being made and to the treatment of the cancer at that time and the patient's likely prognosis.

In the further posts I will look at treatment, prognosis and life expectancy and bringing claims for claimants with reduced life expectancy. I have posted links to resources and authorities here.

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