Objectives: Recent studies of breast cancer data have identified seven distinct clinical phenotypes (groups)
using immunohistochemical analysis and a range of different clustering techniques. Consensus between
unsupervised classification algorithms has been successfully used to categorise patients into these specific
groups, but often at the expenses of not classifying the whole set. It is known that fuzzy methodologies
can provide linguistic based classification rules. The objective of this study was to investigate the use of
fuzzy methodologies to create an easy to interpret set of classification rules, capable of placing the large
majority of patients into one of the specified groups.
Materials and methods: In this paper, we extend a data-driven fuzzy rule-based system for classification
purposes (called ‘fuzzy quantification subsethood-based algorithm’) and combine it with a novel class
assignment procedure. The whole approach is then applied to a well characterised breast cancer dataset
consisting of ten protein markers for over 1000 patients to refine previously identified groups and to
present clinicians with a linguistic ruleset. A range of statistical approaches was used to compare the
obtained classes to previously obtained groupings and to assess the proportion of unclassified patients.
Results: A rule set was obtained from the algorithm which features one classification rule per class,
using labels of High, Low or Omit for each biomarker, to determine the most appropriate class for each
patient. When applied to the whole set of patients, the distribution of the obtained classes had an agreement
of 0.9 when assessed using Kendall’s Tau with the original reference class distribution. In doing so,
only 38 patients out of 1073 remain unclassified, representing a more clinically usable class assignment
algorithm.
Conclusion: The fuzzy algorithm provides a simple to interpret, linguistic rule set which classifies over
95% of breast cancer patients into one of seven clinical groups.