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Metastatic squamous cell carcinoma (SCC) to the skin can be distinguished histologically from primary cutaneous squamous cell carcinoma as, unlike the latter, it is typically separated from the normal overlying squamous epithelium. Rare cases have been reported of cutaneous metastases of SCC that demonstrate continuity with the overlying benign squamous epithelium, termed "epidermotropic cutaneous metastases of SCC." We report the first case of epidermotropic cutaneous metastases of SCC originating from primary esophageal SCC with a review of the literature on this rare histological phenomenon.

Alpha smooth muscle actin (SMA) belongs to the actin proteins. It is a known immunohistochemical marker for tumors of mesenchymal origin. There have been reports of expression of SMA in certain epithelial malignancies in the head and neck and genital regions. In this study, the authors report a primary cutaneous spindle cell squamous carcinoma expressing SMA. Both high- and low-molecular-weight keratins and p63 were positive, and S100 protein, SOX10, MART-1/Melan-A, and muscle-specific actin stains were negative. This case highlights that an epithelial tumor could express a mesenchymal marker, thereby making the diagnosis problematic.

Cutaneous squamous cell carcinoma (SCC) with osteoclast-like giant cells (hereafter, osteoclastic cells) is very rare; eight cases have been reported since 2006. Whether the osteoclastic cells represents a reactive or neoplastic change remains a matter of debate. Osteoclastic cells are often observed in the sarcomatous component of cutaneous carcinosarcoma. SCC with osteoclastic cells is a heterogeneous condition that includes SCC with stromal changes containing osteoclastic cells (also known as osteoclast-like giant cell reaction) and carcinosarcoma. In some cases, SCC with an associated osteoclast-like giant cell reaction has been differentiated from carcinosarcoma based on the degree of cytologic atypia in non-epithelial components. We summarized the clinical and histopathologic characteristics of 11 patients of SCC with osteoclastic cells, including our two cases of SCC with an osteoclast-like giant cell reaction and one case of carcinosarcoma. The affected patients were old and more likely to be male (64%). Seven cases (64%) were in the head and neck. Moreover, multiple features of high risk SCC were observed, such as a tumor size greater than 2 cm (56%), moderate or poor differentiation (100%), recurrence (33%) and nodal metastasis (17%) after excision and immunosuppression (27%). Interestingly, half of the previously reported cases of SCC with osteoclastic giant cell reaction had histopathologic findings that were overlapping with those of carcinosarcoma., (© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

P75 neurotrophin receptor (p75) is a transmembrane protein in the tumor necrosis receptor superfamily useful for the diagnosis of desmoplastic melanomas, desmoplastic trichoepitheliomas, and more recently used for detecting perineural invasion in oral and esophageal squamous cell carcinomas (SCCs). P75 staining in cutaneous SCCs is more controversial with initial staining reported as negative but more recent reports indicating that it may be a useful immunohistochemical marker of perineural invasion. A poorly differentiated pleomorphic epithelioid cell proliferation, which had strong p75 staining in the periphery of epithelioid cell nests, is being reported. Both low and high molecular weight keratins were positive and SOX10, S100, and HMB-45 staining were negative, consistent with a poorly differentiated SCC. To our knowledge, this pattern has not yet been reported and most likely reflects reiteration of the basal layer epithelium, which normally stains positively for p75. Reports of p75 staining in cutaneous SCCs are still limited, and a larger scale study may prove useful in determining its role as a marker for perineural invasion.

Background: Emerging evidence is implicating stem cells in the pathogenesis of different cutaneous neoplasms. The immunohistochemical use of stem cell markers has facilitated stem cell identification. While few studies have examined the expression of cytokertatin (CK)15 and cytokeratin (CK)19 in basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), only rarely have nestin expression been examined in these two malignancies. Furthermore, stem cell marker expression, to the best of our knowledge, has not been examined in Merkel cell carcinoma (MCC)., Methods: In this study, we examined the expression of stem cell markers CK15, CK19 and nestin in 51 overall cases (11 cases of MCC and 20 cases each of BCC and SCC) retrieved from the pathology files of Skin Pathology Laboratory, Boston University School of Medicine., Results: Cytokeratin 15 immunoreactivity was observed in 30% of BCC cases and only a single (5%) SCC case, while all MCC cases were negative. While 60% of BCC cases and 30% of SCC cases stained positively with CK19, all MCC cases showed positive immunostaining in a dot-like pattern. While negative in BCC and MCC, nestin expression was interestingly seen in 45% of SCC cases., Conclusions: Our study described the expression profiles of stem cell markers CK15, CK19 and nestin in BCC, SCC and MCC. In addition to confirming results of the previous reports, our study also showed positive nestin expression in around half of SCC cases, which adds this malignancy to the cutaneous tumours that have been so far reported to exhibit nestin expression., (© 2010 The Authors. Journal of the European Academy of Dermatology and Venereology © 2010 European Academy of Dermatology and Venereology.)

Squamous cell carcinoma in situ (SCCIS) is a frequently reported diagnosis by pathologists. The dermatologists bases their management of the patient on this diagnosis. However, SCCIS can be seen in a variety of clinical situations. The pathologic diagnosis of SCCIS must be correlated with clinical data to arrive at a correct diagnosis and therefore appropriate management of the patient.

Four mixed Merkel cell and squamous cell carcinomas of the skin are described. The patients ranged in age from 74 to 90 years and demonstrated or had a history of previous ultraviolet or infrared damage to the skin, manifested by basal cell carcinoma, squamous cell carcinoma, actinic keratoses, solar elastosis, and erythema ab igne. Light microscopic examination of all 4 cases revealed invasive neoplasms consisting of 2 distinct but admixed cell types. The predominant cell type was consistent with Merkel cell carcinoma and was characterized by scant cytoplasm, a small dark polygonal nucleus with granular chromatin, a high mitotic rate, and cytokeratin 20 positivity. In each case, the Merkel cell component merged with a cytokeratin 20 negative squamous component characterized by abundant eosinophilic cytoplasm, intercellular bridges, and keratinization with focal squamous pearl formation. Immunohistochemical staining patterns were consistent with the usual pattern for that cell type; transitional cells were not demonstrated. The intimate admixture of the 2 antigenically different neoplastic cell types, and common etiologic role of ultraviolet and possibly infrared damage, lend support to the theory that some Merkel cell carcinomas and squamous cell carcinomas may arise from a pluripotent epidermal stem cell.

Background: The term Marjolin ulcer is now synonymous with malignant transformation of chronic ulcers, sinus tracts, and burn scars., Objective: To illustrate the importance of incisional or excisional biopsies in cases of suspected burn scar carcinoma., Methods: Case report and review of the literature., Results: Multiple punch biopsies were negative while a complete excision revealed the diagnosis of squamous cell carcinoma., Conclusion: Because of the focal nature of malignant change in burn scars, incisional or excisional biopsy should be performed.