Heterogeneity describes a set of entities none of which resembles the other.
Heterogeneity is applied by medicine to describe the diversity of tumors.
Medicine postulates that cancer is a genetic disease and each mutation causes a different cancer. For instance hitherto breast cancer was regarded as one disease with heterogeneous manifestations. Today each manifestation is regarded as a different breast cancer!!.
Breast cancer is regarded as a disease conglomerate. Initially breast tumors were classified into three different diseases. Recent study describes ten breast cancer diseases.
Hitherto medicine was perplexed by inter-tumor heterogeneity. Recent studies reveal another heterogeneity source,
intra-tumor heterogeneity.
Genetic studies fragment classical disease into sub types which are regarded as genuine cancers.