LETTERS

TO THE

EDITOR

Desmoplastic Spitz Nevus Combined With Cutaneous Leiomyoma: A Rare Collision Tumor To the Editors: Melanocytic tumors combined with nonmelanocytic cutaneous lesions have often been reported in the literature. Most frequently, melanocytic nevi coexist with epidermal, follicular, and adnexal tumors. The association of melanocytic nevi with mesenchymal proliferations is rare, and it has been previously described mainly with blue nevi. The associated mesenchymal component is usually neural or myomatous. Recently, a series of combined blue nevi with smooth muscle hyperplasia has been published.1 Only 1 case of a cutaneous leiomyoma has been previously reported in the literature in combination with a blue nevus.2 Herein, we report the collision of a cutaneous leiomyoma with an intradermal desmoplastic Spitz nevus. To our knowledge, this is the first case of cutaneous leiomyoma combined with a nevus since 1959 and a unique case of a desmoplastic Spitz combined with cutaneous leiomyoma (Figs. 1 and 2). A 40-year-old man presented to the dermatologist with an asymptomatic lesion on the left thigh. The clinical diagnosis was a traumatized nevus. Histological evaluation revealed part of a nonulcerated poorly pigmented polypoid intradermal melanocytic lesion. The epidermis was slightly acanthotic with some elongation of rete ridges, but there were no features of a junctional melanocytic component or of any follicular induction. The dermal melanocytic component was closely associated with a spindle-cell proliferation and consisted of small nests, strands and individual units of epithelioid melanocytes with eosinophilic cytoplasm, vesicular nuclei and a single basophilic nucleolus. A single mitotic figure was identified in the

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FIGURE 1. Low power view of a domeshaped cellular proliferation expanding the reticular dermis. The papillary dermis is spared. The overlying epidermis is acanthotic, with no junctional component. A nested proliferation of epithelioid cells are seen within a seemingly dense stroma with discernible fascicles at the lower part. The lesion extends to the deep margin.

FIGURE 3. Higher power of nested and single melanocytes with epithelioid morphology intertwined with fascicles of smooth muscle cells. The melanocytes are present within a cross-cut smooth muscle bundle with obvious cytoplasmic vacuolation of the smooth muscle cells.

superficial part of the lesion. Unfortunately, part of the deep component of the lesion was absent for evaluation of maturation and of deep dermal mitoses. No features of regression or inflammation were seen. The spindle-cell component was arranged in well-formed closely packed short bundles and fascicles in close association with single cells and nested melanocytes with little intervening stroma. In areas where stroma was noted, it consisted of desmoplastic collagen. The spindle cells had ovoid to elongated blunt-ended nuclei and eosinophilic cytoplasm and did not show any mitotic activity (Figs. 3 and 4).

By immunohistochemistry, the melanocytic component was highlighted by S100 and Melan A (Fig. 5). The proliferation fraction by MIB 1 was low. The spindle-cell component was positive for smooth muscle actin (SMA), calponin, desmin, and h-caldesmon. The diagnosis of a collision tumor comprising an intradermal Spitz nevus with desmoplastic features and cutaneous leiomyoma was made. The association of melanocytic nevi with other tumors usually involves conventional melanocytic nevi or less often blue nevi. The most common combination is with basal-cell carcinoma

FIGURE 2. On higher power, the fascicular component is reminiscent of smooth muscle cells in intersecting bundles and short fascicles. The epithelioid nested cells are closely intermixed.

FIGURE 4. Close view of the epithelioid Spitz nevus cells with ovoid vesicular nuclei, small basophilic nucleoli and abundant eosinophilic cytoplasm. They are admixed with bland smooth muscle cells.

Am J Dermatopathol  Volume 37, Number 9, September 2015

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Am J Dermatopathol  Volume 37, Number 9, September 2015

FIGURE 5. Combined immunohistochemistry for S100 (brown chromogen) and SMA (red chromogen) highlights the dual population of lesional cells.

and seborrhoeic keratosis. The association of melanocytic nevi with desmoplastic trichoepithelioma is well described. Occasionally, clear cell acanthoma, molluscum contagiosum, and syringoma may also be combined with melanocytic nevi. Recently, 2 cases of trichoblastoma with an intradermal nevus and a blue nevus were reported.3 Histologically, cutaneous leiomyomas are dermal, nonencapsulated, rather well-circumscribed spindle-cell proliferations arranged in interlacing bundles and short fascicles with focal whorled pattern. The cells have elongated blunt-ended nuclei, eosinophilic cytoplasm, and occasional paranuclear vacuoles. Nuclear palisading, Verocay-like bodies, granular cell change focal hyalinization of stroma, rare osseous metaplasia, and focal myxoid change have been reported. On immunohistochemistry, they are positive for SMA, desmin, and h-caldesmon.4,5 Leiomyomas can sometimes be multiple and in some cases of autosomal dominant inheritance, or associated with uterine leiomyomas (Reed syndrome). An association with renal cell papillary or collecting duct carcinoma has also been documented. The most common theories to explain the presentation of such combinations of tumors are the dermal stem cell theory and the theory of neural crest origin. According to stem cell theory, pluripotent stem cells are present in the dermis, with the ability to differentiate toward multiple lineages, including smooth muscle and melanocytic.6 According to the theory of neoplasms of neural crest origin, a heterogeneous group of tumors may derive from

aberrant migration of neural crest cells, as is the case for blue nevi and neurocristic hamartomas.7 In this case, the presence of wellformed bundles and fascicles in a more compact and circumscript silhouette with not much intervening collagen was more in keeping with the appearances of a cutaneous leiomyoma rather than with smooth muscle hyperplasia. In the latter, it is expected to find scattered bundles or fascicles of smooth muscle in a random distribution with no expansion of the dermis. Last but not least, although very rare, tumor in tumor metastasis phenomenon is well described, and caution should be taken to exclude a melanoma metastasizing in a cutaneous leiomyoma. However, the degree of cellular uniformity, lack of mitotic activity, and severe atypia excluded melanoma in this particular case. Eleni Ieremia, FRCPath* Mark Taylor, FRCPath† Eduardo Calonje, DipRCPath* *St John’s Institute of Dermatopathology, St Thomas’ Hospital, London, United Kingdom †Cellular Pathology Department, Brighton and Sussex University Hospital, United Kingdom

REFERENCES 1. Tzu J, Goldman C, Perry AE, et al. Combined blue nevus-smooth muscle hamartoma. J Cutan Pathol. 2013;40:879–883. 2. Montgomery H, Winkelmann RK. Smooth muscle tumours of the skin. Am Arch Derm. 1959;79:32–41. 3. Osio A, Battistella M, Peltre B, et al. Combined trichoblastoma and melanocytic nevus: report of 2 cases widening the spectrum of hair follicle-derived tumors combined with melanocytic nevus. Am J Dermatopathol. 2013;35: 284–286. 4. Calonje E, Thomas B, Lazar A, McKee PH, eds. Connective tissue tumours. In: McKee’s Pathology of the Skin with clinical correlations. 7th ed. Edinburgh: Elsevier/Saunders; 2012. 5. Weedon D, ed. Tumors of muscle, cartilage and bone. In: Weedon’s Skin Pathology. 3rd ed. London: Churchill Livingstone Elsevier; 2010. 6. Li L, Fukunaga-Kalabis M, Herlyn M. Isolation, characterisation and differentiation of human pluripotent dermal stem cells. Methods Mol Biol. 2013;989:235. 7. DeLellis RA, Tischler AS, Wolfe HJ. Multidirectional differentiation in neuroendocrine neoplasms. J Histochem Cytochem. 1984;32: 899.

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Letters to the Editor

On Steatocystoma, Sebaceous Duct Cyst, Isthmic-Anagenic Cyst, and CK19 To the Editor: Sir, I enjoyed reviewing the report, “Cutaneous keratocyst and steatocystoma unified as sebaceous duct cyst, a cystic hamartoma resembling the sebaceous duct.”1 In this report, the authors criticize my hypothesis on the isthmicanagenic cyst as a different type of structure, elaborated in 2008.2 I elaborated this hypothesis when I was young (er) and I further insisted on it, although with no other publication(s). Because of the criticism received by many, I decided to review my hypothesis and also to perform some immunohistochemical studies on this type of cyst. Among these, the most contributory were probably the results with CK19. It is well known that the isthmus commonly expresses cytokeratins (CKs) 5/6, 14, 17, and 19,3 whereas the sebaceous duct does not express CK19 but does express the rest of these.4 In my studies, the type of cysts that I was trying to rename were all CK19 negative, more in consonance with a sebaceous duct origin. I decided to conceptually reevaluate my hypothesis and to realize that it was wrong from the beginning: as Dr. Makhija remarks, the isthmus does not morphologically modify during the hair cycle, therefore, it was nonsense to favor any similarity with the isthmus only in anagen. Currently, I agree with the interpretation that (1) steatocystomas (with or without sebaceous glands) are morphologically similar to the sebaceous duct and (2) the cysts that I interpreted in 2008 as a different type of cyst (isthmic-anagenic) are probably just steatocystomas without sebaceous glands. I think that the concepts regarding the morphology of such types of cysts are very well clarified by the report, “Cutaneous keratocyst and steatocystoma

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Desmoplastic Spitz Nevus Combined With Cutaneous Leiomyoma: A Rare Collision Tumor.

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