merkel cell carcinoma within follicular cysts: report of two cases

J Cutan Pathol 2008: 35: 1127–1133doi: 10.1111/j.1600-0560.2007.00919.xBlackwell Munksgaard. Printed in Singapore

Copyright # Blackwell Munksgaard 2008

Journal of

Cutaneous Pathology

Merkel cell carcinoma within follicularcysts: report of two cases

Merkel cell carcinoma is a rare cutaneous neoplasm of unknownhistogenesis. Several reports have described the association of Merkelcell carcinoma of the skin with other cutaneous neoplasms within thesame lesion, and there are also reports describing three examplesof Merkel cell carcinoma within follicular cysts. We describe twoexamples of Merkel cell carcinoma developed within epithelial cysts.Neoplastic cells of Merkel cell tumor expressed immunoreactivity forchromogranin, synaptophysin, neuron-specific enolase, CAM 5.2and cytokeratin 20, the last two markers showing the characteristicparanuclear dot-like pattern. In contrast, the epithelial wall liningthe cyst and surrounding Merkel cell tumor only expressedimmunoreactivity for cytokeratin MNF116. The description of fivecases of Merkel cell carcinoma within follicular cysts, including the twocases of this report, support some relationship between Merkel celltumor and the hair follicle.

Requena L, Jaqueti G, Rutten A, Mentzel T, Kutzner H. Merkel cellcarcinoma within follicular cysts: report of two cases.J Cutan Pathol 2008; 35: 1127–1133. # Blackwell Munksgaard 2008.

Luis Requena1, GerardoJaqueti1, Arno Rutten2, ThomasMentzel2 and Heinz Kutzner2

1Department of Dermatology, FundacionJimenez Dıaz, Universidad Autonoma, Madrid,Spain, and2Dermatopathologische Gemeinschaftspraxis,Friedrichshafen, Germany

Luis Requena, MD, Department of Dermatology,Fundacion Jimenez Dıaz, Avda. Reyes Catolicos 2,28040-Madrid, SpainTel: 34 91 5447039Fax: 34 91 5442636e-mail: lrequena@d.es

Accepted for publication September 28, 2007

Merkel cell carcinoma, also named cutaneous neuro-endocrine carcinoma or trabecular carcinoma of theskin, is a rare cutaneous neoplasm of unknownhistogenesis. Most authors consider that Merkel cellcarcinoma results from a neoplastic proliferation ofMerkel cells, although conclusive proofs of this originare lacking. Several reports have described theassociation of Merkel cell carcinoma of the skin withother cutaneous neoplasms within the same lesion,including Bowen’s disease,1–3 squamous cell carci-noma,4–6 lentigo maligna7 and benign folliculartumor.8 In the literature, there are also reportsdescribing three examples of Merkel cell carcinomawithin follicular cysts: one case within an infundibularcyst9 and two cases within a tricholemmal cyst.10,11

We describe here two examples of Merkel cellcarcinoma developed within follicular cysts. Thelesions were immunohistochemically studied, andeach component of the lesion showed differentimmunohistochemical profile. Thus, neoplastic cellsof Merkel cell tumor expressed immunoreactivity forchromogranin, synaptophysin, neuron-specific eno-lase, CAM 5.2 and cytokeratin 20, the last two

markers showing the characteristic paranuclear dot-like pattern. In contrast, the epithelial wall lining thecyst and surrounding Merkel cell tumor only ex-pressed immunoreactivity for cytokeratin MNF116,which showed the different nature of the neoplasticcells of Merkel cell carcinoma and the epithelial cellsof the cyst wall. Although a histogenetic relationshipbetween Merkel cell tumor and the epithelialcomponent of cutaneous adnexa has been suggested,that relationship remains speculative. The recentdemonstration of numerous Merkel cells at theinfundibulum and the isthmus, including the bulgeportion,12–15 as well as in the outer root sheath,16 ofthe normal hair follicle, as well as the finding ofMerkel cell hyperplasia associated to somebenign andor malignant adnexal neoplasms with folliculardifferentiation raise the possibility of some histoge-netic relationship betweenMerkel cell carcinoma andthe hair follicle.17–20 The description of five cases ofMerkel cell carcinoma within follicular cysts, includ-ing the two cases of this report, also supports somerelationship between Merkel cell tumor and the hairfollicle.

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Case reports

Case 1

A 69-year-old man was seen with a tumor on the righthip. The clinical diagnosis was �soft tissue tumor’ andthe lesion was excised. After initial histopathologicdiagnosis of Merkel cell carcinoma within a cyst, thetumor was re-excised but only scar tissue was found inthe re-excised specimen. Two years later, there was noevidence of recurrence or metastases.

Case 2

A67-year-oldmanwas seenwith a softmass on the leftelbow. Clinical diagnosis was ganglion cyst and thelesion was excised. One year later, there was noevidence of recurrence or metastatic disease.

Histopathologic findings

The two cases basically showed identical histopath-ologic findings. At scanningmagnification, the lesionsshowed a cystic configuration and involved the fullthickness of the dermis with no connection with theoverlying epidermis. The cystic structure was lined bysquamous epithelium. In case 1, the epithelial walllining Merkel cell carcinoma was composed of cordsand thin strands of basaloid cells, which anastomosedin a reticulated pattern (Fig. 1). In some areas, smallinfundibular cyst containing orthokeratotic, baso-philic keratin arranged in laminated layers waspresent within these epithelial cords. Adjacent to themain mass of the tumor, there was a second smallercystic structure lined by the same type of epitheliumthan the previous one and containing homogeneouseosinophilic material and cholesterol crystals. No

Fig. 1. Case 1. A) Scanning power showing two cystic lesions involving the dermis. The upper cyst contained homogeneous eosinophilic

material, whereas the lower cyst was filled by solid aggregations of basophilic cells. B) Higher magnification showed epithelial cords at the cyst

wall and small round basophilic cells in the cyst contents. C) Higher magnification showed that neoplastic cells showed high nuclear-

cytoplasmic ratio, inconspicuous cytoplasm and vesicular nuclei with smudged or clear granular chromatin. D) The epithelial cords forming

the cyst wall contained also small keratinous cysts.

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neoplastic aggregations of Merkel cell carcinomawere present within this small cystic structure andserial sections failed to show connection between thetwo cystic structures. In case 2, the epithelial cysticwall showed the stereotypical features of tricholem-mal keratinization, namely a basal layer, 5–10 layersof squamous keratinocytes, absence of granular layerand compact eosinophilic orthokeratotic keratin

(Fig. 2). This tricholemmal keratin filled most of thecystic cavity, although some areas of infundibularkeratin represented by basophilic, orthokeratotic,laminated corneocytes were also seen within thecystic contents. In some areas, from the cystic wallemanated epithelial cords of variable thickness thatextended to the pericystic dermis. These cordsappeared to be composed of basophilic keratinocytes

Fig. 2. Case 2. A) Scanning power showing a cystic lesion containing eosinophilic keratin. Note small aggregations of basophilic cells in the

upper part of the cystic contents. B) Higher magnification of the basophilic cells showed that they showed the characteristic nuclear and

cytoplasmic features of the neoplastic cells of Merkel cell carcinoma. C) The cyst wall was composed of squamous epithelium. D) Higher

magnification showed that the epithelium of the cyst wall showed tricholemmal keratinization. E) At the periphery of the cyst, epithelial cords

with an anastomosing pattern emanated from the cyst wall. F) These epithelial cords were composed of squamous cells and contained tiny

keratinous cysts.

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that anastomosed in reticulated pattern and con-tained small infundibular cysts. The most strikingfeature in both cases consisted of the presence of solidaggregations of small round basophilic cells within thecystic cavity. These cells showed a high nuclear-cytoplasmic ratio, inconspicuous cytoplasm, vesicularnuclei with smudged or clear granular chromatin andusually a single, centrally located small nucleolus.Numerous mitotic figures, single necrotic cells andsmall areas of necrosis en masse were present.

Immunohistochemistry showed that neoplasticsmall round basophilic cells expressed immunoreac-tivity for cytokeratin 20 (clone Ks 20.8, dilution1 : 40; Dako, Glostrup, Denmark) (Figs. 3 and 4),pankeratin cocktail AE1/AE3 (dilution 1 : 500;Dako), CAM 5.2 (dilution 1 : 60; Becton Dickinson,San Jose, CA, USA), synaptophysin (clone Sy38,dilution 1 : 10; Dako), chromogranin (clone DAK-A3, dilution 1 : 2; Dako) (Fig. 4) and neuron-specificenolase (clone BBS-NC-V, dilution 1 : 500; Dako).

The immunostaining of neoplastic cells for CAM 5.2and cytokeratin 20 showed a characteristic dot-likepattern in neoplastic cells of case 1 and a more diffusepattern of immunostaining in neoplastic cells of case 2(Figs. 3 and 4). In contrast, the epithelial cyst wall onlyexpressed immunoreactivity for cytokeratinMNF116(dilution 1 : 50; Dako) (Fig. 5).

Discussion

The presence of Merkel cell carcinoma withina follicular cyst is a rare event and a review of theliterature shows only five examples of this association,including the two cases of this report (Table 1). Twocases consisted of Merkel cell carcinomas withininfundibular cysts and other two were Merkel celltumors within tricholemmal cysts. In one case (case 1of this report), the nature of the cyst could not becompletely established, but the histopathologic char-acteristics of the epithelium of the cystic wall and the

Fig. 3. Case 1. Immunostaining for CK20. A) Scanning power showing CK20 positivity only of the cyst contents. B) Higher magnification

showed strong immunoreactivity of neoplastic cells for CK20. C) Still higher magnification showed that the positivity for CK20 was mostly

within the cytoplasm of neoplastic cells. D) Still higher magnification showed that CK20 immunoexpression showed a paranuclear dot-like

pattern.

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epithelial cords that emanated from this wall alsosupported a follicular origin for the cystic lining.However, five examples of this event probablyrepresent lesions that result to be more frequentthan what would be expected by chance as a simplecollision lesion and support the notion that in somecases Merkel cell carcinomas and the follicular cystsoriginated from the same histologic structure.Merkel cells are normal components of thebasal layer

of the epidermis, but they cannot be identified with theroutine hematoxylineosin stains. Immunohistochemicaland/or ultrastructural studies are necessary to highlightthem. Immunohistochemically, Merkel cells expresscytokeratin 20 and CAM 5.2, usually both markerswith a characteristic pattern of dot-like immunostaining,as well as neuroendocrine markers such as chromogra-nin, synaptophysin and neuron-specific enolase. Ultra-structurally, Merkel cells are characterized by thepresenceof cytoplasmic electron-dense granules, strandsof intermediate filaments and occasional desmosomesconnecting them with neighboring keratinocytes.Recently, several studies have investigated the

distribution of Merkel cells in fetal and adult terminalhair follicles.13–16 These studies have shown thatMerkel cells aremainly grouped in two clusters withinthe normal hair follicle: one at the deep infundibulum

and the other at the isthmus. No significant number ofMerkel cells was identified in the lower segment of thefollicle, including the bulb and the follicular papilla. Arelatively high concentration of Merkel cells wasfound at the level of the bulge,14,15 which is thefollicular structure that marks the limit between theisthmus and the lower segment of the hair follicle andis the site for arrector pili muscle insertion. The bulgeappears to be composed of several undifferentiatedbasophilic keratinocytes arranged in protuberancesand ridges and seems to be that these keratinocytesbehave as stem cells during the hair cycle.21 Thus,because Merkel cells are numerous at the infundib-ulum and the isthmus, it is probable that Merkel cellcarcinomas arising within infundibular or tricholem-mal cysts result from neoplastic proliferations ofthe normal Merkel cell constituents of the hairfollicle. Supporting this notion, numerous Merkelcells have been also found scattered within theneoplastic aggregations of several neoplasms withfollicular differentiation, including desmoplastic tri-choepithelioma,19 trichoblastoma,22 follicular prolif-erations in nevus sebaceous,20 trichofolliculoma,23

and fibroepithelioma of Pinkus.24 All these findings,however, do not confirm the origin of the reportedMerkel cell carcinomaswithin follicular cysts from the

Fig. 4. Case 2. A) Immunostaining for CK20. B) Higher magnification showed that neoplastic cells of this case showed a more diffuse pattern

of immunostaining for CK20 than the neoplastic cells of the case 1. C) Immunostaining for chromogranin. D) Higher magnification showed

a granular pattern of immunoexpression for chromogranin within the cytoplasm of neoplastic cells.

Merkel cell carcinoma within follicular cysts

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Merkel cells normally presentwithin the epitheliumofthe hair follicle and this relationship remains asspeculative.

In conclusion, Merkel cell carcinoma may rarelydevelop within follicular cysts. The presence ofnumerous Merkel cells in the infundibulum and

isthmus of the hair follicle as well as the abundantnumber of Merkel cells in some neoplasms withfollicular differentiation suggest that in these casesthere may be some histogenetic relation between thehair follicle and theMerkel cell carcinoma rather thansimply collision lesions.

Fig. 5. Case 1. Immunostaining for cytokeratin MNF116. A) Scanning power showing immunoreactivity of the epidermis, the adnexa and the

epithelium lining the two cystic structures of the dermis. B) Higher magnification showed the MNF116 immunoreactivity of the epithelial

cords of the cyst wall whereas the neoplastic small round cells of the cyst contents resulted negative. C) At the periphery, there was sharp

contrast between the MNF116 immunoexpression of the epithelial cords and the negative results of the neoplastic small round cells of the cyst

contents. D) Higher magnification showing the MNF116 immunoexpression of the epithelial cords and the negative results of neoplastic cells

of Merkel cell carcinoma.

Table 1. Summary of the cases of Merkel cell carcinoma developed within follicular cysts

References Age (years) Sex Location Clinical diagnosis Histopathologic findings Follow up

Perse et al.9 58 M Thigh Epidermal cyst Merkel cell carcinoma within the wall of aninfundibular cyst

Inguinal adenopathy

Collina et al.10 65 F Forearm ND Merkel cell carcinoma within a tricholemmal cyst NDPagetoid spread into tricholemmal epithelium

Ivan et al.11 86 M Thigh ND Merkel cell carcinoma within a tricholemmal cyst NDPagetoid spread into tricholemmal epithelium

This report 69 M Right hip �Soft tissue tumor’ Merkel cell carcinoma within a follicular cyst NERM 2 years later67 M Left elbow Ganglion cyst Merkel cell carcinoma within a tricholemmal cyst NERM 1 year later

F, female; M, male; ND, not described; NERM, no evidence of recurrence or metastatic disease.

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References

1. Sibley RK, Dehner LP, Rosai J. Primary neuroendocrine

(Merkel cell?) carcinoma of the skin. I. A clinicopathologic and

ultrastructural study of 43 cases. Am J Surg Pathol 1985; 9: 95.

2. Kroll MH, Toker C. Trabecular carcinoma of the skin. Arch

Pathol Lab Med 1982; 106: 404.

3. LeBoit PE, Crutcher WA, Shapiro PE. Pagetoid intraepidermal

spread in Merkel cell (primary neuroendocrine) carcinoma of

the skin. Am J Surg Pathol 1992; 16: 584.

4. Tang C-K, Nedwich A, Toker C, Zaman ANF. Unusual

cutaneous carcinoma with features of small cell (oat-cell like)

and squamous cell carcinoma. Am J Dermatopathol 1982;

4: 537.

5. Gomez LG, Silva EG, DiMaio S, Mackay B. Association

between neuroendocrine (Merkel cell) carcinoma and squa-

mous carcinoma of the skin. Am J Surg Pathol 1983; 7: 171.

6. Iacocca MV, Abernethy JL, Stefanato CM, Allan AE, Bhawan

J. Mixed Merkel cell carcinoma and squamous cell carcinoma

of the skin. J Am Acad Dermatol 1988; 39: 882.

7. Heenan PJ, Cole JM, Spagnolo DV. Primary cutaneous

neuroendocrine carcinoma (Merkel cell tumor). Am J Derma-

topathol 1990; 12: 7.

8. Yamamoto O, Tanimoto A, Yasuda H, et al. A combined

occurrence of neuroendocrine carcinoma of the skin and

a benign appendageal neoplasm. J Cutan Pathol 1993; 20: 173.

9. Perse RM, Klappenbach RS, Ragsdale BD. Trabecular (Merkel

cell) carcinoma arising in the wall of an epidermal cyst. Am J

Dermatopathol 1987; 9: 423.

10. Collina G, Bagni A, Fano RA. Combined neuroendocrine

carcinoma of the skin (Merkel cell tumor) and trichilemmal

cyst. Am J Dermatopathol 1997; 19: 545.

11. Ivan D, Bengana C, Lazar AJ, Diwan AH, Prieto VG. Merkel

cell tumor in a trichilemmal cyst: collision or association. Am J

Dermatopathol 2007; 29: 180.

12. Moll I, Roeslsler M, Brandner JM, et al. Human Merkel cells –

aspects of cell biology, distribution and functions. Eur J Cell

Biol 2005; 84: 259.

13. Narisawa Y, Hashimoto K, Kohda H. Epithelial skirt and bulge

of human facial vellus hair follicles and associated Merkel cell-

nerve complex. Arch Dermatol Res 1993; 285: 269.

14. Narisawa Y, Hashimoto K, Nakamura Y, et al. A high con-

centration ofMerkel cell in the bulge prior to the attachment of the

arrector pili muscle and the formation of the perifollicular nerve

plexus in human fetal skin. Arch Dermatol Res 1993; 285: 261.

15. Narisawa Y, Kohda H. Two- and three-dimensional demon-

stration of morphological alterations of early anagen hair

follicle with special reference to the bulge area. Arch Dermatol

Res 1996; 288: 98.

16. Moll I. Merkel cell distribution in human hair follicles of the

fetal and adult scalp. Cell Tissue Res 1994; 227: 131.

17. Abesamis-Cubillan E, El-Shabrawi-Caelen L, LeBoit PE.

Merkel cells and sclerosing epithelial neoplasms. Am J

Dermatopathol 2000; 22: 311.

18. Gould VE, Moll R, Moll I, et al. Biology of disease:

neuroendocrine (Merkel) cells of the skin: hyperplasias,

dysplasias, and neoplasms. Lab Invest 1985; 52: 334.

19. Hartschuh W, Schulz T. Merkel cells are integral constituents of

desmoplastic trichoepithelioma: an immunohistochemical and

electron microscopic study. J Cutan Pathol 1995; 22: 413.

20. Schulz T, Hartschuh W. Merkel cells in nevus sebaceus. Am J

Dermatopathol 1995; 17: 570.

21. Cotsarelis G, Sun T-T, Lavker RM. Label-retaining cells reside

in the bulge area of the pilosebaceous unit: implications for

follicular stem cells, hair cycle and skin carcinogenesis. Cell

1990; 61: 1329.

22. Schultz T, Hartschuh W. Merkel cells are absent in basal cell

carcinomas but frequently found in trichoblastomas: an

immunohistochemical study. J Cutan Pathol 1997; 24: 477.

23. Hartschuh W, Schultz T. Immunohistochemical investigation of

the different developmental stages of trichofolliculoma with

special reference to the Merkel cells. Am J Dermatopathol

1999; 21: 8.

24. Hartschuh W, Schultz T. Merkel cell hyperplasia in chronic

radiation-damaged skin: its possible relationship to fibroepithe-

lioma of Pinkus. J Cutan Pathol 1997; 24: 477.

Merkel cell carcinoma within follicular cysts

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