Background The stroma of basal cell carcinoma (BCC) is rich in mast cells. Morpheaform BCC has been reported to contain many more mast cells than the other types of BCC. However, pathogenesis and clinical relevance of this observation are currently unclear. Smoking and ultraviolet (UV) exposure have recently been suggested to be related to the development of morpheaform BCC.
Methods With a retrospective study, we aimed to investigate the possible roles of smoking and occupational UV exposure in the development of morpheaform BCC through the quantification of peritumoral mast cells. Our case population consisted of 34 patients with morpheaform BCC and 50 patients with solid BCC. After identification of mast cells with toluidine blue stain, a mast cell index was determined in each case.
Results Mean mast cell index of morpheaform BCCs was significantly higher than that of solid BCCs (P < 0.02). Increased mast cell indices were associated with smoking (P = 0.003), but not with UV exposure (P > 0.05), irrespective of the tumor type. Morpheaform BCC was significantly more frequent in smokers compared to solid BCC (P < 0.05). In the cases with morpheaform BCC, mean mast cell index of smokers was significantly higher than that of nonsmokers (P = 0.02). Mean mast cell index of smokers with morpheaform BCC was also significantly higher than that of the smokers with solid BCC (P = 0.04). Ultraviolet exposure alone had no significant influence on mast cell indices, nor on the frequency of morpheaform BCC.
Conclusion We suggest that smoking can play a key role in the differentiation of BCC toward its sclerosing form, through the increased peritumoral mast cell numbers.