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Cutaneous Carcinoma with Mixed Histology: A Potential Etiology for Skin Cancer Recurrence and an Indication for Mohs Microscopically Controlled Surgical Excision

Cutaneous carcinomas with mixed histology describe nonmelanoma skin cancers which have more than one histologic subtype. These include basal cell carcinomas with concurrent aggressive growth patterns (such as sclerosing, infiltrating, micronodular, keratinizing, and tumors with perineural involvement) and nonaggressive growth patterns (such as superficial, nodular, and follicular) and squamous cell carcinomas with concurrent poorly differentiated and well-differentiated components. One mechanism of recurrence of nonmelanoma skin cancer may very well result from the inadequate initial treatment of cutaneous tumors with mixed histology. If the aggressive histologic subtype of the original tumor is initially not suspected based upon the pathology observed from a superficial biopsy specimen, the clinician may initiate therapy that would be appropriate for the less aggressive variant that was diagnosed. Subsequently, the more aggressive tumor may persist and eventually manifest as a clinical recurrence of the cancer. This is particularly important when there is perineural tumor involvement. We describe two patients whose skin cancers had more than one histologic subtype to demonstrate the histologic features of cutaneous malignancies with more than one pathologic pattern and to emphasize how inaccurate a single diagnostic biopsy can be. We also suggest that clinicians consider Mohs surgical excision of nonmelanoma skin cancers since this technique incorporates microscopically controlled removal of the tumor with complete pathologic evaluation of all surgical margins for any residual cancer.