Probably all pathologists agree that proliferations of stromal cells represent a somewhat complex chapter of pathology. In fact, their classification is still tentative, full of synonyms and with confusing terms, such as “inflammatory tumour” or “pseudosarcomatous proliferation”.

Several factors can contribute to this complexity: a possible common progenitor (fibrocyte)1 for fibroblasts and myofibroblasts; the fact that the fibrocyte can be considered as belonging to the leucocytes; the possible epithelial origin of mesenchymal cells (epithelial–mesenchymal transition); and the interconnections between physiological and pathological stromal proliferations.2

The absence of a satisfactory classification provided by …