Basal cell carcinoma and demodicidosis: Is there an etiologic or coincidental relationship?

Although solar irradiation is the major factor in the development of basal cell carcinoma (BCC), some other factors also seem to play an etiopathogenetic role regarding the fact that relatively sun-protected areas are also often involved. Pilosebaceous follicle mites, Demodex folliculorum and Demodex brevis are found most frequently and densely in the same facial areas including eyelids, forehead, nasal and periauricular regions where basal cell carcinomas also appear more commonly than elsewhere. We therefore investigated whether there is an etiopathogenetic relationship between demodicidosis and BCC. We evaluated a total of 142 histopathologic skin specimens which include at least 5 pilosebaceous units, taken from 94 cases with BCC and from 48 healthy subjects with benign skin lesions. The demodicidosis rate and mean demodex number were found significantly higher in BCC cases (44.68%, and 0.872±1.193, respectively) than those in controls (25%, and 0.458±1.009, respectively) (p<0.05). Mite frequency was significantly higher in the periorbitally located BCCs as compared to other locations (p<0.05), while it did not differ significantly among the histologic subtypes of BCC (p>0.05). Conclusively, demodicidosis can be one of the predisposing factors which contribute to the carcinogenesis process of BCC, by causing perifollicular chronic inflammation or by its traumatic effect. Another explanation for these results would be that an age-related decline in immunity may be responsible for the increased mite positivity and mite numbers in BCC cases, or these findings may indicate only a coincidental relationship between demodicosis and BCC, but not an etiologic one. [Turk J Cancer 2000;30(3):111-118]