This video from "Five Minute Pathology Pearls" discusses the proper interpretation of CD31 immunostaining in pathology, particularly in the context of differentiating vascular tumors like angiosarcoma from other high-grade sarcomas. Dr. Gardner highlights that CD31 can nonspecifically stain histiocytes and even some tumor cells in a weak, patchy, and granular pattern, which should not be mistaken for true endothelial differentiation. He emphasizes using the crisp, strong staining of normal background blood vessels as an internal control to assess the significance of CD31 positivity. The video provides guidance on when to consider additional vascular markers like ERG or CD34 to avoid misdiagnosing a non-vascular tumor as an angiosarcoma.
CD31 Staining: Differentiating Specific from Non-Specific Positivity in Pathology
0:02 CD31 Nonspecific Staining: CD31 can stain histiocytes and sometimes tumor cells nonspecifically, which does not indicate endothelial or vascular differentiation.
0:19 Case Example - High-Grade Sarcoma: A high-grade pleomorphic sarcoma with hemorrhage initially raised concerns for angiosarcoma due to CD31 staining.
0:40 Comparing Staining Patterns: Normal background vessels show crisp, dark CD31 staining. In contrast, histiocytes and tumor cells often exhibit weak, patchy, granular staining.
1:23 Histiocyte Staining is Normal: It is normal for histiocytes to stain with CD31 in a weak, granular fashion.
1:48 Internal Control for Interpretation: Pathologists should compare the staining intensity in tumor cells to the crisp, strong staining in normal background blood vessels, which serve as an internal control.
1:59 Angiosarcoma CD31 Staining: Angiosarcomas typically show strong, diffuse positivity for CD31.
2:11 Exceptions and Additional Markers: While CD31 is a primary vascular marker, exceptions exist (e.g., CD34 loss in some angiosarcomas, CD31 negativity in some Kaposi sarcomas). If unsure, additional vascular markers like ERG can be used.
2:27 Key Takeaway - Not Endothelial Differentiation: Weak, blushy, or patchy CD31 staining is generally not indicative of true endothelial differentiation.
3:01 Avoid Overcalling Angiosarcoma: The crucial point is to avoid misinterpreting nonspecific CD31 staining and overcalling a non-vascular lesion as an angiosarcoma.