Immunohistochemical markers

[azkid]

My mom recently had a biopsy with immunohistochemical staining being performed.  They are sending it out to Mayo for a second opinion.  Her results are as follows:  pancytokeratin (strong positive); cytokeratin 7 (strong positive); cytokeratin 20 (negative); HMB-45 (negative); Melan A (positive); S-100 (negative).  The confusion is that the tumor is strongly cytokeratin positive, yet shows expression of melan A.   My understanding is that it is most likely breast cancer when the CK 7 is positive and the CK 20 is negative (as her's is).  With metastatic melanoma, wouldn't the HMB-45 and S-100 usually be positive in addition to the Melan A?  How could she have metastatic melanoma when no one can find a primary skin lesion?  They are questioning whether she also might have lymphoma as the lymph nodes are markedly enlarged, as well.

[azkid]

Second pathology markers came back negative for melanoma.  They are sending it off to Vanderbilt University for their pathologists to review.  They say it is "confounding."

[Cleveland Clinic]

Dear askid, Immunohisotchemical staining is used as an ancillary test to assist in making a pathological diagnosis.  Many different stains can be used to help suggest one diagnosis over another, but are often not definitive.  As certain stains are usually not 100% specific and sensitive, they must be used in the context of the patient’s presentation including clinical characteristics such as age and other risk factors, physical exam, and radiology studies.  Melanoma can present with metastatic disease without an identifiable primary lesion.  Again, some of the stains mentioned can be helpful to diagnose melanoma, but are not perfect.  We agree with obtaining the assistance of the pathologists at Mayo Clinic who may have more specialized experience in this case.