Infantile desmoid-type fibromatosis. Morphological features correlate with biological behaviour.

It is generally agreed that the biological behaviour of infantile desmoid-type fibromatosis is unpredictable in terms of the likelihood of local recurrence. We evaluated the prognostic importance of the number of slit-like blood vessels with a mean diameter of less than 20 microns and of the quantity of undifferentiated mesenchymal cells. In addition, we studied the immunophenotypic characteristics of the proliferating cells and their nucleolar organizer region (AgNOR) numbers and distribution. Statistical analysis showed that the tendency to recur locally was correlated with larger numbers of slit-like blood vessels and undifferentiated mesenchymal cells. The proliferating cells were identified by immunohistochemistry as myofibroblasts. No correlation was found between AgNOR numbers and clinical course of the disease. We conclude that histological features easily evaluated by conventional light microscopy provide useful information on the possible course of infantile desmoid-type fibromatosis.