Skin is CK- and Vulvar Paget is CK+.

• A. Skin CK-, Vulvar Paget CK+
• B. Skin CK+, Vulvar Paget CK-
• C. Skin CK-, Vulvar Paget CK-
• D. Skin CK+, Vulvar Paget CK+

Answer: (C)

The idea here is how a cytokeratin (CK) immunostain pattern can vary depending on which CK is being tested. Different CKs are expressed in different epithelial tissues, and the staining outcome depends on the specific CK antibody used.

In this scenario, the result is that both the normal skin and the vulvar Paget cells would be CK negative for the particular CK being considered. That makes the only consistent choice the pattern where both tissues are CK negative. It emphasizes that, with immunostains, you must pay attention to which CK is being detected, since different CKs can yield different positivity in the same tissues.

In typical practice, vulvar Paget disease cells often show CK7 positivity, while skin keratinocytes express other keratins; but this question focuses on a specific CK panel where both tissues are CK negative, hence the correct match.