Alteration of mast cell proliferation/apoptosis and expression of stem cell factor in the regression of mastocytoma--report of a case and a serial immunohistochemical study.

Background: Spontaneous regression of solitary mastocytoma is a well-described phenomenon, but its mechanism is unknown.

Methods: Serial-section immunohistochemical analyses were performed on biopsies of a mastocytoma from a Japanese child during the proliferation stage (PS, 7 months of age) and the regression stage (RS, 5 years old).

Results: Mast cell (MC) density in RS was markedly decreased (406 cells/mm2) compared to that in PS (3554 cells/mm2). MCs in RS were larger than those in PS. With proliferative cell nuclear antigen (PCNA) staining, 1.7% MCs were positive in PS, whereas no positive MCs were seen in RS. TUNEL-labeling index (LI) in RS (2.8%) increased 1.5-fold in PS (1.9%). With stem cell factor (SCF) staining, 57% of lesional MCs in RS revealed strong cytoplasmic immunoreactivity, whereas only 9% of MCs were positive in PS. Epidermal SCF reactivity was found as intracellular and intercellular patterns in both PS and RS.

Conclusions: Loss of MC proliferating activity, an increase in apoptotic MCs, and increased expression of SCF in remaining MCs in RS may play a role in the involution of mastocytomas.