When someone has had treatment for breast cancer they, very understandably, usually want to know whether or not they have been cured.

Like all types of cancer, breast cancer is an unpredictable condition and no one can ever be absolutely certain of the outcome of treatment. Over the years, however, doctors have found a number of factors which give an indication of how successful treatment might be.

Three of these factors are:

• the size of the cancer
• whether or not the cancer has spread to the lymph nodes (otherwise known as lymph glands) under the arm (and if so, how many nodes are affected)
• the grade of the cancer: this is based on the appearance of the tumour under the microscope and is an indication of how aggressive the cancer is.

Some years ago breast cancer specialists in Nottingham worked out a formula, bringing these three things together, which could be used to help give an idea of the chances of a cure. This has become known as the Nottingham Prognostic Index (NPI).

The formula is:

NPI = (0.2 x tumour diameter in cms) + lymph node stage + tumour grade

The lymph node stage is either 1 (if there are no nodes affected), 2 (if up to 3 glands are affected) or 3 (if more than 3 glands are affected). Similarly the tumour grade is scored as either 1 (for a grade I, less aggressive appearance), 2 (for a grade II, intermediate appearance) or 3 (for a grade III, more aggressive appearance).

Applying the formula gives scores which fall into three bands:

• a score of less than 3.4 - this suggests a good outcome with a high chance of a cure
• a score of between 3.4 to 5.4 - this suggests an intermediate level with a moderate chance of cure
• a score of more than 5.4 - this suggests a worse outlook with a smaller chance of cure.

The NPI was based on information from a group of patients treated some time ago and as a result of improvements in treatment it may underestimate the outlook for a person (prognosis). So although the NPI is a useful guide it is not absolutely reliable and there will always be many people whose NPI predictions do not match the reality of their individual outcomes. So the NPI is a useful guide but not a guarantee of what will happen.