Adenosquamous carcinoma: finding the critical diagnosis in the squamous cell carcinoma commonplace. Anna Sarah Erem; Zachary Wolner; Travis Blalock; Douglas Parker.

Summary: Primary cutaneous adenosquamous carcinoma (ASC) is a rare malignant neoplasm with squamous and glandular morphologic growth patterns, local aggressive behavior, and increased risk of metastasis. While the tumor classically presents on the face or scalp, it can present on the upper and lower extremities, with rare reports in other areas. ASC is widely considered a high-risk histologic pattern of cutaneous squamous cell carcinoma. Here, we present two cases of primary ASC. The first case is a 65-year-old male with no significant medical history who presented with an erythematous, scaly nodule on the nasolabial fold measuring 1.7 cm in diameter. The second case is a 67-year-old female with a 3.6 cm erythematous to red, eroded plaque on the left shoulder. Biopsies in both cases demonstrated a biphasic tumor, displaying a moderately to poorly differentiated squamous epithelium that transitioned into epithelium displaying glandular features. Immunohistochemistry for cytokeratin 7 and CAM5.2 was positive in the glandular component and negative in the squamous component. Cytokeratin 5/6 was positive in the squamous and glandular component, supportive of ASC. The first case required multiple resections secondary to positive margins, but the patient has no evidence of disease 18 months after diagnosis. The second case was recently excised with negative margins. These cases illustrate the importance of recognizing adenosquamous carcinoma due to its propensity for locoregional recurrence and highlight the role of immunohistochemistry in supporting the diagnosis.