Rosai-Dorfman disease (RDD) is a rare but distinctive clinicopathologic entity of unknown etiology affecting lymph nodes as well as extranodal sites. Although cutaneous involvement in RDD is common, purely cutaneous disease is rare and not well documented. We report 22 patients with cutaneous and superficial subcutaneous RDD. The lesions presented as papules and nodules, often with discoloration (9/22) and frequent multifocality (13/22), without predilection for a specific site of the body. Age distribution was wide and ranged from 15 to 68 years, with a median of 43.5 years. Of the 17 patients for whom information on racial background was available, 7 were Asian, 8 were white, and 2 were black, with a marked female predominance (2:1). The lesions resolved in 6 of 13 patients for whom follow-up data were available, regardless of the treatment given. Lesions persisted or recurred in 7 patients. Histologically, the lesions are invariably characterized by a proliferation of polygonal S100-positive histiocytes showing emperipolesis and a mixed inflammatory infiltrate. This study characterizes the histologic spectrum of cutaneous RDD in regard to variation in the numbers of typical S100-positive histiocytes and emperipolesis, variation in the quality and quantity of the inflammatory response, and the degree of stromal fibrosis, which resulted in a strikingly storiform growth pattern in six lesions and a lobulated pattern in two lesions. Whereas the clinical as well as histologic appearance of the cutaneous and subcutaneous lesions in the purely extranodal forms of RDD is indistinguishable from that of systemic RDD, this study emphasizes that purely cutaneous RDD is a distinct clinical entity in regard to its epidemiology and remains localized to the skin even with long-term follow-up. Patients with purely cutaneous RDD are of an older age at onset of disease (median = 43.5 years), with a reversed male/female ratio. There are no significant systemic extracutaneous or serologic manifestations. Whereas systemic RDD is commonly seen in blacks and only rarely reported in Orientals, the majority of the patients in this series with purely cutaneous RDD are Asians and whites.

This review provides a comprehensive overview of the broad clinicopathologic spectrum of cutaneous Kaposi sarcoma (KS) lesions. Variants discussed include: usual KS lesions associated with disease progression (i.e. patch, plaque and nodular stage); morphologic subtypes alluded to in the older literature such as anaplastic and telangiectatic KS, as well as several lymphedematous variants; and numerous recently described variants including hyperkeratotic, keloidal, micronodular, pyogenic granuloma-like, ecchymotic, and intravascular KS. Involuting lesions as a result of treatment related regression are also presented.

The authors present a series of 24 malignant neoplasms arising in preexisting benign spiradenoma (20), cylindroma (2), and spiradenocylindroma (2). Nineteen patients (12 females, 7 males; age range, 41 to 92 y) had a solitary neoplasm (size range, 2.2 to 17.5 cm; median 4 cm), whereas the remaining 5 (4 females, 1 male; age range, 66 to 72 y) manifested clinical features of Brooke-Spiegler syndrome (BSS), an autosomal dominantly inherited disease characterized by widespread, small, benign neoplasms on which background larger malignant lesions appeared. Microscopically, all cases showed the residuum of a preexisting benign neoplasm. The malignant components of the lesions were variable and could be classified into 4 main patterns, occurring alone or in combination: 1) salivary gland type basal cell adenocarcinoma-like pattern, low-grade (BCAC-LG); 2) salivary gland type basal cell adenocarcinoma-like pattern, high-grade (BCAC-HG); 3) invasive adenocarcinoma, not otherwise specified (IAC-NOS); and 4) sarcomatoid (metaplastic) carcinoma. In 1 case of IAC-NOS, an in situ adenocarcinoma was also found, presumed to have evolved from an adjacent adenomatous and atypical adenomatous component. Cases harboring a sarcomatoid carcinoma featured a malignant epithelial component composed of varying combinations of BCAC-HG, BCAC-LG, IAC-NOS, or squamous cell carcinoma, whereas the sarcomatoid component appeared as either a pleomorphic or spindle-cell sarcoma. Additionally, in 2 cases there were foci of heterologous chondrosarcomatous differentiation and in 1 case there was rhabomyosarcomatous differentiation. Of the 21 patients with available follow-up (range, 3 mo-15 y; average 4.8 y; median 3.5 y), 10 were without evidence of disease, 1 was alive with metastatic disease, 1 was alive with BSS, 3 developed local recurrences, 4 had died of disease, and 2 were dead of other causes. The histologic pattern of the malignant neoplasm correlated to some extent with the clinical course. BCAC-LG neoplasms showed a less aggressive course, with local recurrences but no distant metastases, whereas the BCAC-HG neoplasms typically followed a highly aggressive course resulting in the death 3 of 6 patients with BCAC-HG. Patients with sarcomatoid carcinoma had a relatively good survival. Molecular genetic investigations revealed no mutations in the CYLD gene in the 4 sporadic cases investigated. One patient with BSS revealed a novel missense germline mutation in exon 14 (c. 1961T>A, p. V654E), whereas a living descendant of another deceased patient demonstrated a recurrent nonsense germline mutation in exon 20 (c. 2806C>T, p. R936X). Given the morphologic diversity and complexity of the neoplasms in question, we propose using a more specific terminology with the precise description of the neoplasm components, rather than generic and less informative terms such as "spiradenocarcinoma" or "carcinoma ex cylindroma."

Mutations in beta-catenin are present in benign pilomatrixomas. beta-catenin is a downstream effector in the WNT-signalling pathway, acting as a signal for differentiation and proliferation. Mutations in CTNNB1, the gene encoding beta-catenin, are present in a wide variety of benign and malignant neoplasms. We examined beta-catenin in a series of pilomatrix carcinomas (15 cases) by using immunohistochemistry and DNA sequencing of exon 3 from CTNNB1, and compared these to a series of benign pilomatrixomas (13 cases). All 11 pilomatrix carcinomas available for examination showed nuclear localization of beta-catenin and mutations in exon 3 similar to those demonstrated in benign pilomatrixomas. Two of 11 pilomatrix carcinomas showed significant nuclear accumulation of p53, whereas this was absent in all 13 benign pilomatrixomas. Expression of nuclear cyclin D1 was similar in both benign pilomatrixomas and pilomatrix carcinomas. Clinical follow-up from the 15 malignant cases reported in this study and by others indicates that wide excision offers superior control of local recurrence, compared to simple excision. Immunohistochemical and molecular analysis of beta-catenin reveals that both pilomatrix carcinomas and benign pilomatrixomas harbour mutations in beta-catenin. This implies a common initial pathogenesis and is compatible with the proposition that pilomatrix carcinomas may at least on occasion arise from their benign counterparts.

The findings suggest a possible role for ultraviolet radiation and chronic immunosuppression in the induction of malignant squamous differentiation in a subset of EPCs. Further reports on this histological variant of EPC are required to determine whether a pathogenetic link does indeed exist or whether these tumours simply represent a unique variant of squamous cell carcinoma with divergent acrosyringial differentiation.

Cutaneous sebaceous neoplasia is known to exhibit a high degree of DNA mismatch repair (MMR) deficiency leading to microsatellite instability and these tumors can be markers of the Muir-Torre syndrome and internal malignancy. Other tumors, such as colonic carcinoma, show tendencies toward particular histologic features and sites of involvement correlating with MMR deficiency. There are few comprehensive studies of unselected cutaneous sebaceous neoplasms. To address this gap in knowledge, we examined 94 sebaceous neoplasms from 92 patients and 17 sebaceous hyperplasia controls using immunohistochemistry for MLH1, MSH2, and MSH6. Our results indicate that MMR deficiency is significantly associated with anatomic location (more frequently in the trunk and extremities as compared with head and neck), tumor type (more often in adenoma compared with carcinoma within the head and neck region), and architecture (keratoacanthomalike). No correlation between cystic change and MMR deficiency was noted. Cutaneous sebaceous neoplasia has tendencies toward certain tumor types and anatomic distribution based on MMR status analogous to that seen in colonic carcinomas and other tumors. These may be helpful indicators for further workup for the Muir-Torre syndrome.

Rosai-Dorfman disease (RDD), previously known as sinus histiocytosis with massive lymphadenopathy, is a benign, idiopathic histiocytic proliferative disorder. It commonly affects lymph nodes, but any organ of the body may be involved. Histological findings include characteristic large, pale, histiocytic cells (Rosai-Dorfman cells) exhibiting cytophagocytosis. Immunohistochemically, these histiocytes are positive for S-100 protein and CD68, but stain negatively for CD1a. On electron microscopy, Birbeck granules are absent. RDD limited to the skin is rare, less than 30 cases having been reported to date. We present five further cases of purely cutaneous RDD. Three presented as solitary nodules and one as a large, well-circumscribed plaque. The fifth patient, who was HIV positive, had a rosacea-like facial eruption.

Primary cutaneous apocrine carcinoma is a rare malignancy. This study of 24 examples suggests that the prognosis is not always poor and that grading criteria devised for breast carcinoma may have utility in this group of malignancies. Furthermore, steroid receptor expression should be investigated in these tumors, particularly if a tumor is unlikely to be controlled by surgery alone.