Calretinin is a
calcium-binding protein member of the EF-hand family. The presence of
calretinin has been demonstrated in certain stages of the cellular cycle in a wide variety of normal and neoplastic tissues. The main aims of our study were (1) to investigate what structures of the normal skin and cutaneous adnexal proliferations express immunoreactivity for
calretinin and (2) to determine the value of immunohistochemical expression for
calretinin as a marker for follicular, sebaceous, apocrine, and eccrine differentiation in cutaneous adnexal proliferations. We studied 139 biopsy specimens, including 10 cases of normal skin of different locations and 129 benign and malignant cutaneous adnexal proliferations. In normal skin, we found that
calretinin is expressed in the innermost cell layer of the outer root sheath in anagen hair follicle, in both the duct and sebolemma of the sebaceous gland, in the secretory portion of eccrine glands, and in mast cells of the stroma. In cutaneous adnexal proliferations, we found strong immunoreactivity for
calretinin in tricholemmal
cysts, tricholemmomas/inverted follicular
keratoses,
tumors of follicular infundibulum, and in some
basal cell carcinomas. Focal positivity was also seen in trichoadenomas, trichoblastomas/trichoepitheliomas, pilomatricomas, proliferating tricholemmal
tumors,
pilar sheath acanthomas, trichofolliculomas, follicular hybrid
cysts, cutaneous mixed
tumors, steatocystomas, sebaceous
hyperplasias, and sebaceomas. These results demonstrate that immunohistochemical study for
calretinin may be helpful to identify the innermost cell layer of the outer root sheath in anagen hair follicle and the cutaneous adnexal proliferations showing differentiation toward this structure.
Calretinin immunoreactivity supports eccrine differentiation in some
sweat gland neoplasms, and it is also useful in identifying
neoplasms with ductal sebaceous differentiation.