If a stain is Melan-A positive and PAX8 negative, which statement matches?

• A. CK7, CDX2
• B. TTF-1, PAX8
• C. Melan-A positive; PAX8 negative
• D. Melan-A positive; PAX8 positive

Answer: (C)

Immunohistochemical profiling helps identify where a tumor comes from by looking at lineage-specific markers. Melan-A is a marker of melanocytic differentiation, so a tumor that is Melan-A positive points toward melanoma. PAX8, on the other hand, is expressed in renal, thyroid, and Müllerian-derived tissues; if PAX8 is negative, those origins are unlikely. Therefore, the statement that matches the observed pattern is Melan-A positive and PAX8 negative, which supports a melanocytic tumor rather than a carcinoma from kidney, thyroid, or Müllerian structures. The other marker combinations would suggest different tissue origins and do not align with the Melan-A positive, PAX8 negative profile.