Shadow Cell Basal Cell Carcinoma With Acantholysis

John Kwittken, MD

I present histologic documentation of a unique infundibula in association with suprabasilar clefts basal cell carcinoma (BCC) in which shadow containing dyskeratotic acantholytic cells. cells formed the major cellular component along Clear spaces that ranged from small circular with extensive acantholysis and the development zones to clefts of variable length were randomly of ringed shadow cells. This neoplasm contained scattered throughout the neoplasm. A relatively trichohyalin granules, which are indisputable small number of these spaces, primarily linear, did evidence of follicular differentiation. Shadow not possess an epithelial cell lining and undoubt- cells rarely are encountered within BCCs and edly represented stromal retraction artifact. The generally form relatively small components. Such majority of spaces were either completely or par- neoplasms have been labeled BCC with matrical tially lined by a single layer of palisaded basaloid differentiation. Because of nonspecificity and cells (Figure 1). The small circular zones appeared ambiguity, I propose that this terminology be adenoid or glandular. Many of these spaces con- abandoned and replaced by shadow cell BCC. tained clusters of acantholytic and focally dysker- atotic basaloid cells and rounded shadow cells hadow cells rarely are encountered within basal (Figure 2). The cytoplasms of many of these cell carcinomas (BCCs).1,2 When present, shadow cells were filled with concentric lamina- Sshadow cells comprise relatively small portions tions of . Basaloid cells with crescent- of the neoplasm. Such neoplasms have been labeled shaped nuclei were attached to and either partially BCC with matrical differentiation. My purpose is to or totally encircled by many of the shadow cells report a unique case of a BCC in which not only did that I labeled ringed shadow cells (Figure 3). shadow cells form the major cellular component but There was a broad range of histologic patterns also were associated with striking acantholysis. I within the neoplasm. At one end of the spectrum therefore propose a different terminology for this was the characteristic pattern of stromal prolifera- form of BCC. tion with retraction artifact and peripheral palisad- ing of basaloid cells with an orderly gradual Case Report progression of shadow cell formation. The sequence A 64-year-old Caucasian man presented with an was as follows: a proliferation of several layers of ulcerated circular papule involving the right tem- basaloid cells with varying amounts of amphophilic ple. It measured 0.8 cm in diameter and had been to faintly eosinophilic cytoplasms that were focally present for almost one year. A 4-mm punch biopsy vacuolated, the formation of transitional cells (cells was performed, followed by an excisional biopsy with degenerating and necrotic nuclei), the transi- 2 months later. tion into shadow cells, and the termination into Histologically, the lesion proved to be a rare form compactly laminated keratin with focal calcifica- of BCC. The lesion was deeply invasive and tion. In other areas, the transition into shadow extended to involve approximately the upper half of cells was relatively abrupt, with little or no basaloid the subcutaneous tissue. Shadow cells formed the cell proliferation or transitional cells (Figure 4). At major cellular component. Focally, this neoplasm the other end of the spectrum, the neoplastic cells was connected to both the and showed severe anaplasia. This was characterized by disorderly dyskeratotic cells with focally vacuolated cytoplasms, pleomorphic hyperchromatic nuclei, From the Veterans Administration Medical Center, Phoenix, Arizona. and frequent mitoses. Acantholysis also was present Reprints: John Kwittken, MD, 7930 E Camelback Rd, Bldg 25, in these zones. This was evident by either partially B104, Scottsdale, AZ 85251. coherent or slightly separated neoplastic cells

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A B Figure 1. An invasive neoplasm replaces much of the dermis. The neoplasm is composed primarily of shadow cells and smaller numbers of basaloid cells intermingled with randomly scattered small circular spaces and variable-length clefts lined by a layer of palisaded basaloid cells. Mainly linear clear spaces without an epithelial cell lining represent stromal retraction artifact (arrowheads, B). This neoplasm is connected directly to both the epidermis (arrow, A) and an infundibulum (arrow, B) in association with suprabasilar clefts containing dyskeratotic acantholytic cells. Note the merging of shadow cells with a large, ovoid, basophilic zone of calcification at right margin (B)(H&E, original magnifications 40).

associated with an intermingling of rounded or cutaneous appendages. The basaloid cell is the diag- ringed shadow cells (Figure 5). nostic hallmark of this neoplasm and often may con- Trichohyalin granules, refractile granules that tain mucin, melanin, and lipid within its cytoplasm. assume various sizes and shapes and stain brightly Commonly, the basaloid cell shows squamous differ- eosinophilic with hematoxylin and eosin (H&E), entiation and becomes keratinized. Frequently, were identified within the cytoplasms of many mucin, amyloid, and melanin within melanophages basaloid cells (Figure 6). Brown melanin granules, and dendritic melanocytes are observed within its which appeared black with the Fontana-Masson stroma. Rarely, shadow cells form relatively small stain, were observed within dendritic melanocytes, components of BCCs.1,2 Trichohyalin granules3 have basaloid cells, melanophages, and shadow cells in also been identified within these BCCs.3 many areas (Figure 7). No mucin could be demon- Using the routine H&E stain, the typical strated within the neoplastic cells. Relatively large shadow cell is recognized as a fully keratinized poly- amounts of hyaluronic acid were observed within hedral cell with an abundant eosinophilic cytoplasm, the stroma with special stains. a generally well-defined cytoplasmic border, and a central circular or oval empty space corresponding Comment to the lost nucleus. When found within the skin, BCC of the skin is the most common primary inva- the shadow cell has been considered to represent a sive cancer of the human body. It may assume a vari- faulty attempt at the formation of a shaft and is ety of histologic patterns including solid, cystic, indicative of follicular differentiation. Besides adenoid, sclerosing, keratotic (with horn cysts), and being a characteristic hallmark of the piloma- creeping. It may show either no evidence of differ- trixoma, shadow cells have been identified within a entiation or differentiation toward any or all of the variety of pathologic processes involving the

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Figure 2. The adenoid pattern is surrounded by sheets of shadow cells and clefts of variable length (arrows) that contain clusters of acantholytic and focally dyskeratotic basaloid cells and rounded shadow cells (H&E, original magnification 100).

Figure 3. The cleft is lined by a single layer of palisaded basaloid cells, and lumen contains acantholytic dyskeratotic basaloid cells and rounded shadow cells filled with concentric laminations of keratin. Arrow points to a ringed shadow cell (H&E, original magnification 400). of all 3 embryologically derived funda- and onychomycosis.12 Extracutaneous ectodermally mental tissues—ectoderm, mesoderm, and ento- derived shadow cells have been observed within a derm. In addition to BCC and pilomatrixoma, calcifying odontogenic cyst,13 an intracranial ectodermally derived cutaneous lesions include dermoid cyst,14 and a pilomatrixoma of the testis.15 ; trichoepithelioma4; mixed tumor of With 2 exceptions, the shadow cells within the the skin4-6; pilomatrix carcinoma,7 even within aforementioned lesions probably represent faulty metastases8; epidermal cysts of Gardner’s syn- attempts at follicular differentiation. Shadow cells drome9; proliferating pilomatrixoma10; matricoma; within onychomycosis probably represent a faulty melanocytic matricoma11; condyloma acuminatum; attempt to form the plate. Shadow cells within

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Figure 4. Stromal proliferation with, from left to right, retraction artifact, peripheral palisading of basaloid cells, a proliferation of several layers of basaloid cells with varying amounts of amphophilic to faintly eosinophilic and focally vacuolated cytoplasms, tran- sitional cells, shadow cells, and compactly laminated keratin with focal calcification. In other areas, the transfor- mation into shadow cells was relatively abrupt (arrow- head), with little or no basaloid cell proliferation or transitional cells (H&E, original magnification 100).

Figure 5. Severe anaplasia within a zone of acantholysis. Note the 2 metaphase mitoses (lower center) and the disorderly dyskeratotic cells with focally vacuolated cytoplasms and pleomorphic hyperchromatic nuclei. Many of the cells are either partially coherent or slightly sepa- rated with an intermingling of rounded and ringed shadow cells throughout (H&E, origi- nal magnification 400).

the calcifying odontogenic cyst probably represent a include endometrial adenocarcinoma with squa- final product of cell death from squamous metapla- mous cell differentiation and atypical endometrial sia derived from enamel epithelium. hyperplasia with squamous differentiation.16,19 In Entodermally derived lesions include adenocar- these lesions, the shadow cells, as noted within the cinoma of the colon with squamous differentia- calcifying odontogenic cyst, probably developed tion16; rectal adenocarcinoma, including lymph from squamous metaplasia. node metastasis17; transitional cell carcinoma of It recently has been shown that the shadow cells the urinary bladder18; and small cell carcinoma of in pilomatrixomas are a mode of cell death that 19 the gallbladder. Mesodermally derived lesions CONTINUED ON PAGE 63

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Figure 6. Large, deeply eosinophilic trichohyalin granules (arrow) within the cytoplasms of a few basaloid cells and acantholytic changes similar to those described in Figure 5 (H&E, original magnification 400).

Figure 7. Coarse black melanin granules within a large dendritic melanocyte (center) and a melanophage (lower left)(arrow). Fine, dustlike, black melanin granules are present within virtually all of the basaloid cells and shadow cells depicted (Fontana-Masson stain, original magnification 400).

CONTINUED FROM PAGE 60 tholytic, pseudoglandular) squamous cell carci- develop from terminal differentiation of transitional noma,23 proliferating pilomatrixoma,10 and piloma- cells, and represent an attempt to form hair (ie, fol- trix carcinoma.7 The adenoid squamous cell licular differentiation).20 It is believed, however, carcinoma and this lesion share the features of ecto- that their formation is not necessarily specific for dermally derived keratinocytes, continuity with the terminal differentiation into hair.21,22 This has been epidermis, suprabasilar clefts containing dyskera- well documented within the nonsquamous, extracu- totic acantholytic cells, and an invasive neoplasm taneous neoplasms previously described. In my view, with pseudoglandular formations containing dysker- this lesion must be differentiated from 3 neoplasms atotic acantholytic cells. The major differences are that appear histologically aggressive: adenoid (acan- the presence of shadow cells and, in this case,

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trichohyalin granules, which do not appear in squa- containing variants of many neoplasms of the pilar mous cell carcinomas of any type. Additionally, the apparatus have been reported, they are uncommon. clefts and pseudoglandular formations in this case Additionally, the vacuolated cytoplasms observed are lined by basaloid cells, not dyskeratotic squa- within the basaloid cells in this case probably are mous cells, as are observed within the adenoid indicative of lipid content, a commonly encoun- squamous cell carcinoma. Also, many of the tered component of BCCs. acantholytic cells are shadow cells, often ringed by The pilar apparatus is a complex miniature organ basaloid cells (ringed shadow cells). The significant comprising , sebaceous gland, apocrine features suggestive of squamous cell carcinoma are gland, arrector muscle, and haarscheibe (hair disk). observed within the zones showing severe anaplasia. The pilar apparatus comes into existence embry- Although uncommon, it is not rare to find similar ologically through a continuous interaction between areas within BCCs. Proliferating pilomatrixoma and ectodermal and mesodermal components. The hair pilomatrix carcinoma are deep-seated nodules of follicle is the most conspicuous part. Trichohyalin, a variable size involving dermis and subcutaneous tis- substance related to , occurs normally sue. The former is generally well circumscribed, within the cytoplasms of the keratinizing cells of the while the latter is poorly delineated and often inner and hair . With the H&E invades subcutaneous fat and skeletal muscle. Both stain, trichohyalin appears as bright, homogeneous, lesions contain cystic zones of variable size filled deeply eosinophilic, refractile structures of variable with keratinous debris along with a stromal foreign size and shape, ranging from fine granules to large body reaction to keratin, calcium, and calcified rounded or irregular bodies. Melanocytes are ecto- shadow cells. Both lesions primarily are composed of dermal cells derived from the neural crest and are peripheral aggregations of basaloid cells that merge, normal components of the matrix of a pigmented either abruptly or gradually via transitional cells, hair. Melanin is produced within these melanocytes with shadow cells. The basaloid cells in proliferat- and incorporated through phagocytosis of distal por- ing pilomatrixoma resemble normal hair matrix tions of dendritic processes into the future hair cells. cells. These basaloid cells are small rounded cells The final product, the hair shaft, is composed pri- with scanty, pale eosinophilic cytoplasms and circu- marily of hard keratin (cortex) without nuclei and lar nuclei with finely stippled chromatin and dis- with varying amounts of melanin. Melanin, keratin, tinct nucleoli. Mitoses may be numerous. There and lipid are normal components of the pilar appa- may be variable nuclear atypia. Scattered necrotic ratus. Besides melanin and keratin, lipid deposits basaloid cells are frequently observed. Although also probably were present in this case. None of ulceration may be present, these basaloid cells do these components is proof of follicular differentia- not communicate with the epidermis or tion. The presence of trichohyalin, however, is spe- infundibula. By way of contrast, the basaloid cells of cific and represents incontrovertible evidence of pilomatrix carcinoma range from those resembling pilar differentiation. normal hair matrix cells to severely anaplastic cells Acantholysis means a pathologic loss of cohesion with large hyperchromatic and pleomorphic nuclei among keratinocytes of stratified squamous epithelia and frequent mitoses, many abnormal, with varying that is discernible with light microscopy. Although amounts of cytoplasm. Foci of necrosis are common this term originally was restricted to lesions involv- and often extensive. Ulceration is not unusual. Pilo- ing epidermis, follicular epithelium, and oral matrix carcinoma may show connections to the epi- mucosa, adenoid squamous cell carcinoma has been dermis but not to infundibula. Trichohyalin included. It most often develops within an acan- granules have been identified within the basaloid tholytic . In acantholysis, there is a cells of both lesions. breakdown of the forces of cohesion, which are Histologically, this case differs fundamentally intercellular substance and intercellular-attachment from these 2 neoplasms. This is due to the absence devices or desmosomes. It may be primary, such as of basaloid cells resembling normal hair matrix cells, occurs in pemphigus vulgaris, whereby the intracel- the presence of peripheral palisading of basaloid lular morphology appears normal under light cells with stromal retraction artifact, the presence of microscopy. It also may be secondary, such as what acantholysis, the absence of cystic zones, the occurs in adenoid squamous cell carcinoma and in absence of a foreign body reaction, and the presence this case, whereby acantholysis develops because of of connections to both the epidermis and dyskeratotic changes. infundibula. The presence of melanin in this case In pemphigus vulgaris, electron microscopy has lends further support for the diagnosis of BCC. It is demonstrated that the tonofilaments within the a frequent component of BCCs. Although melanin- acantholytic cells retract from the cell periphery

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and exhibit perinuclear aggregation. The spaces 2. Ambrojo P, Aguilar A, Simón P, et al. Basal cell carcinoma with resulting from the loss of cohesion become filled matrical differentiation. Am J Dermatopathol.1992;14:293-297. with an influx of tissue fluid from the dermis. The 3. Ackerman AB, DeViragh PA, Chongchitnant N. acantholytic cells, occurring singly and in clusters, Neoplasms With Follicular Differentiation. Philadelphia, Pa: become rounded (actually spherical) within this Lea & Febiger; 1993. fluid. I believe that this shape is a result of a com- 4. Jacobson M, Ackerman AB. “Shadow” cells as clues to fol- bination of factors. These include loss of cohesion, licular differentiation. Am J Dermatopathol. 1987;9:51-57. uniform total surface tension (hydrostatic pressure) 5. Requena L, Yus ES, Santa Cruz OJ. Apocrine type of whereby the cells assume the smallest possible sur- cutaneous mixed tumor with follicular and sebaceous dif- face, and cell resilience, which is aided by an alter- ferentiation. Am J Dermatopathol. 1992;14:186-192. ation in internal architecture. 6. Akasaka T, Onodera H, Matsuta M. Cutaneous mixed Cell death is inevitable and may occur normally tumor containing ossification, hair matrix, and sebaceous or abnormally. It normally is seen in the continu- ductal differentiation. J Dermatol. 1997;24:125-131. ous shedding of soft keratin from the epidermis and 7. Green DE, Sanusi ID, Fowler MR. Pilomatrix carcinoma. the formation of hard keratin of nails and hair (all J Am Acad Dermatol. 1987;17:264-270. dead keratinized cells without nuclei). Within the 8. Mir R, Cortes E, Papantoniou PA, et al. Metastatic various lesions previously discussed, shadow cells trichomatricial carcinoma. Arch Pathol Lab Med. appear to represent an abnormal mode of cell death 1986;110:660-663. through faulty keratinization and, depending on 9. Narisawa Y, Kohda H. Cutaneous cysts of Gardner’s their locale, may be indicative of hair or nail-plate syndrome are similar to follicular stem cells. J Cutan differentiation or represent a mode of cell death Pathol. 1995;22:115-1211. from squamous metaplasia. BCCs containing 10. Kaddu S, Soyer HP, Wolf IH, et al. Proliferating piloma- shadow cells have been labeled BCC with matrical trixoma. J Cutan Pathol. 1997;24:228-234. differentiation. I believe that this terminology is 11. Carlson JA, Healy K, Slominski A, et al. Melanocytic nonspecific and ambiguous. Although not specifi- matricoma: a report of two cases of a new entity. Am J cally stated, this term is presumed to refer to the Dermatopathol. 1999;21:344-349. hair matrix. The skin, however, has other matrices. 12. Fanti PA, Varotti C, Tosti A. “Shadow” cells as clues to fol- There are nail matrix cells, epidermal matrix cells, licular differentiation. Am J Dermatopath. 1988;10:372-375. and adnexal matrix cells, which include those of 13. Gorlin RJ, Pindborg JJ, Redman RS, et al. The calcifying the hair matrix. Furthermore, the meaning is odontogenic cyst. Cancer. 1964;17:723-729. unclear. Does the term indicate that the neoplastic 14. Hitchcock MG, Ellington KS, Friedman AH, et al. cells are differentiating to form a hair shaft or that Shadow cells in an intracranial dermoid cyst. Arch Pathol they are forming hair matrix cells? The latter cer- Lab Med. 1995;119:371-373. tainly is not the case in these neoplasms. In my 15. Minkowitz G, Lee M, Minkowitz S. of the opinion, one simply should call this neoplasm as testis. Arch Pathol Lab Med. 1995;119:96-99. one sees it. Therefore, I recommend that these 16. Zamecnik M, Michal M. Shadow cell differentiation in lesions be called shadow cell BCCs with the under- tumours of the colon and uterus. Zentralbl Pathol. standing that the shadow cells are indicative of fol- 1995;140:421-426. licular differentiation. 17. Nakayama H, Kimura A, Okumichi T, et al. Metaplastic In summary, I have presented a unique case of shadow cells in rectal adenocarcinoma: report of a case a BCC in which shadow cells formed the major with immunohistochemical study. Jpn J Clin Oncol. cellular component. Not previously reported to 1997;27:427-432. my knowledge, this case also exhibited extensive 18. Zamecnik M, Michal M, Mukensnabl P. Shadow cells in acantholysis associated with a striking pattern of extracutaneous locations [letter]. Arch Pathol Lab Med. ringed shadow cells. This neoplasm contained 1996;120:426-428. trichohyalin granules that represent incontrovert- 19. Zamecnik M, Michal M, Mukensnabl P. Pilomatrixoma-like ible evidence of follicular differentiation. For the visceral carcinomas [letter]. Histopathology. 1998;33:395. purpose of specificity and clarity, I propose that 20. Nakamura T. A reappraisal on the modes of cell death in BCCs containing shadow cells be labeled shadow pilomatrixoma. J Cutan Pathol. 1999;26:125-129. cell BCC. 21. Zamecnik M, Michal M, Mukensnabl P. Cell death in pilomatrixoma [letter]. J Cutan Pathol. 2000;27:100. REFERENCES 22. Nakamura T. Cell death in pilomatricoma [letter reply]. 1. Aloi FG, Molinero A, Pippione M. Basal cell carcinoma J Cutan Pathol. 2000;27:100. with matrical differentiation. Am J Dermatopathol. 23. Lever WF, Schamburg-Lever G. Histopathology of the Skin. 1988;10:509-513. 7th ed. Philadelphia, Pa: JB Lippincott Co; 1990.

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