:Primary cutaneous mucinous carcinoma is a rare, indolent malignancy with a debated history regarding cell of origin. Recurrence is rare but has been documented in up to a third of cases. Recent literature reviews have recognized 2 possible subtypes—neuroendocrine and nonneuroendocrine— with different possible prognostic implications for patients. We describe a case of recurrent primary cutaneous mucinous carcinoma in a 50-year-old man with subtle neuroendocrine features not initially recognized on routine H&E staining but highlighted by immunohistochemical studies. We underscore the importance of immunohistochemical use in these rare cases and emphasize that awareness of these neuroendocrine and nonneuroendocrine subtypes is essential for a complete diagnosis.

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Background Benign lichenoid keratosis (BLK) is a cutaneous lesion that can clinically mimic malignancy and may represent regression of a pre‐existing lesion. BLK may show epidermal pseudo‐nests prompting evaluation for a melanocytic lesion. False positivity of MART‐1/Melan‐A immunostaining in pseudonests has been showed; however, the value of SRY‐related HMG‐box 10 (SOX10) staining in BLK with features suspicious for a melanocytic proliferation has not been previously reported. Methods Twenty‐one cases of BLK from 2015 to 2020 were identified. Slides were reviewed and SOX10 immunohistochemistry was performed on each case. Subsequently, Melan‐A immunohistochemical staining was performed on all cases. Results In 10 cases (47.6%), unexpected SOX10 staining was seen in rare to numerous small, single cells in the epidermis above the basal cell layer. No malignancy was identified. Of the 10 cases, 8 (80%) showed suprabasal SOX10 staining did not show similar suprabasal Melan‐A staining; 2 (20%) cases showed scattered suprabasal cells positive for Melan‐A. Conclusion SOX10 immunostaining in BLK can highlight scattered cells in the epidermis (not easily noticeable on routine stain). Performing SOX10 immunostain alone on BLK can prompt a misdiagnosis of a melanocytic lesion and should be done with caution.

:Herpesvirus infection classically presents as a clustered, vesicular rash over mild erythema. However, unusual presentations may mimic tumors and be a potential pitfall. We describe the case of a 55-year-old HIV positive woman with this unusual manifestation of a common disease which was initially diagnosed as a benign neoplasm. Review of pathology revealed histologic features characteristic of this form of herpesvirus eruption. Awareness of this rare clinical and microscopic presentation is important to guide appropriate use of immunostains, prevent misdiagnosis, and promptly institute of antiviral therapy.