We compared the patterns of keratin 10 (K10) and keratin 17 (K17) expression in epidermoid cysts, trichilemmal cysts, eruptive vellus hair cysts, and steatocystoma multiplex. Epidermoid cysts expressed K10 and eruptive vellus hair cysts expressed K17, whereas trichilemmal cysts and steatocystoma multiplex showed expression of both K10 and K17. Our findings support the opinion that eruptive vellus hair cysts, which stained negative for K10, and steatocystoma multiplex are distinct entities and not variants of one disorder.

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The most frequent cutaneous side effect reported in this series was acneiform eruption. The authors observed that all women with acneiform rash had only limited facial involvement, whereas all but one man experienced more widespread lesions of the face, the back and the chest. We found no association between the extent and severity of cutaneous eruptions (grade 1 vs. grade 2) and patients' response to therapy.

Topical pre-treatment with phytomenadione cream might become useful in epidermal growth factor inhibitor-associated acneiform eruptions.

Bak (bcl-2 homologous antagonist/killer) is a proapoptotic member of the ever-expanding bcl-2 gene family, a recently described category of oncogenes that is critical for the regulation of programmed cell death. We investigated the expression of bak in several inflammatory and neoplastic skin diseases in comparison with normal skin. Immunohistochemical analysis revealed positive bak staining in epidermal keratinocytes of normal skin, with the granular layer being stained slightly more strongly than the basal and spinous layers, and in psoriasis vulgaris, lichen planus, actinic keratosis, keratoacanthoma and squamous cell carcinoma. We demonstrated the expression of bak in the follicular infundibulum in contrast to the outer root sheath of the lower follicle, which showed only negative to weak bak expression. Seventeen of 20 basal cell carcinomas examined showed negative immunostaining for bak, and the remaining three basal cell carcinomas showed only partial weak positivity, mainly in the palisading layers of some tumour formations. Immunoblot analysis using cultured normal human epidermal keratinocytes revealed the presence of bak protein in both undifferentiated and differentiated keratinocytes. The results of our study suggest that the loss of bak expression, in conjunction with the previously reported overexpression of bcl-2, might contribute to the pathogenesis of basal cell carcinoma.