Correction to: British Journal of Cancer (2008) 99, 423–427, doi:10.1038/sj.bjc.6604532

Owing to an error during typesetting, there was a mistake introduced in Duffy's formula in this paper when first published in British Journal of Cancer in July 2008.

The formula was contained within the ‘Materials and Methods’ section and should have appeared, thus:

The publishers are happy to correct this mistake.