Dermatopathology
Basal cell (trichoblastic) carcinoma: Common expression pattern for epithelial cell adhesion molecule links basal cell carcinoma to early follicular embryogenesis, secondary hair germ, and outer root sheath of the vellus hair follicle: A clue to the adnexal nature of basal cell carcinoma?

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Background

Basal cell carcinoma (BCC) is still viewed by many dermatologists as a tumor of the interfollicular epidermis, although references were made early in the dermatopathologic literature to the resemblance of BCC to the hair follicle.

Objective

Our aim was to characterize the common expression pattern for the epithelial cell adhesion molecule (Ep-CAM) in BCCs, various stages of follicular embryogenesis, and adult hair follicles and, thereby, in analogy point to the similarity between BCC and the hair follicle.

Methods

We studied immunohistochemically 16 superficial BCCs for Ep-CAM and compared the expression pattern with that during hair follicle, nail, and eccrine gland development in human embryos and fetuses. In addition, we examined terminal scalp and vellus hair follicles.

Results

All BCCs expressed Ep-CAM similar to the early stages of the embryonic human hair follicle, the secondary hair germ, and the outer root sheath of the vellus hair follicle. The embryonic nail organ and the adult anagen hair follicles were completely negative.

Limitations

The conclusions are based on the similarity in the immunohistochemical expression profile for a single adhesion molecule.

Conclusion

BCC expresses the cell-cell adhesion molecule Ep-CAM similar to the embryonic hair germ, the secondary hair germ of the terminal hair follicle, and the outer root sheath of the vellus hair follicle. We suggest that this may be a clue to the adnexal nature of BCC and propose that BCC is the most primitive follicular tumor.

Section snippets

Specimens

Skin samples from 30 human embryos and fetuses between the ages of 9 and 25 weeks of gestation were obtained from elective abortions performed in 1989 in Germany and in the Netherlands. The specimens were collected in conjunction with the guidelines enacted in both countries. The ages of the embryos and fetuses were determined by measuring the foot length.12, 13 and are reported in weeks after conception. Twenty scalp specimens from 22 of the total of 30 embryos and 29 feet samples from 24 of

Results

Ep-CAM is expressed early at the pregerm stage (Fig 1, A) of follicular embryogenesis, and can be found at low levels in the epithelial component (Fig 1, B). The immunopositivity increases dramatically in the subsequent germ stage (Fig 1, C) where strong expression for the Ber-Ep4 antigen becomes apparent in the entire epithelial component but not in the surrounding condensed mesenchymal cells (Fig 1, D). The pattern of expression for Ep-CAM changes again in the hair peg stage (Fig 1, E),

Discussion

In contrast to tumors with unequivocal signs of follicular differentiation (eg, the papillary mesenchymal bodies in trichoepithelioma or the shadow cells imitating the hair matrix in pilomatricoma), BCC has a less obvious follicular nature when observed in hematoxylin-eosin–stained sections. The lack of morphologic clues of follicular differentiation in most BCCs relates to the primitive features of the tumor. The morphologic resemblance of BCC, especially of the superficial type, to the hair

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    Funding sources: None.

    Conflicts of interest: None declared.

    Reprints not available from the authors.

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