Expression of stem cell factor in basal cell carcinoma.

Stem cell factor (SCF) distribution in basal cell carcinomas (BCCs) was examined by immunohistochemistry. Eighteen BCCs (11 nodular, three superficial, two cystic, one adenoid and one morphoeic type) showed positive expression of SCF in the tumour islands. The centre of the tumour island was strongly positive in nodular, superficial and morphoeic types. In cystic BCCs, SCF-positive tumour cells were also located in the peripheral lesion around the cystic space. SCF was also detected on fibroblast-like cells and mast cells in the stroma. SCF was positively stained within the upper keratinocytes in the overlying epidermis, more strongly as compared with normal skin. The mast cell number (mean +/- SD) was significantly increased in the peritumoral stroma (85.7 +/- 28.3/mm2) compared with normal skin (32.1 +/- 4.2/mm2) (P < 0.005). SCF was also positive in the tumour nests of four cases of tricho-epithelioma, in which fibrosis of the surrounding stroma was found histologically. This study demonstrates that abundant SCF produced by the tumour cells may account for the increased number of stromal mast cells, which induce fibroplasia of the surrounding stroma.