Can ER, PR, and HER2-neu Be Obtained from Malignant Pleural Effusion?
Yes, ER, PR, and HER2 status can and should be obtained from malignant pleural effusion specimens when feasible, as receptor status may differ from the primary tumor and directly impacts treatment decisions.
Why Testing Pleural Effusion is Important
The ASCO guideline explicitly recommends retesting ER, PR, and HER2 in metastatic sites because receptor status can be discordant between primary tumors and metastases 1. When discordance exists, the panel consensus is to use the receptor status from the metastasis (in this case, the pleural effusion) to direct therapy, if supported by the clinical scenario and patient's goals 1.
Technical Feasibility and Reliability
Testing on pleural effusion specimens is technically reliable:
- Cell block preparation from pleural fluid allows accurate immunohistochemistry (IHC) testing for ER, PR, and HER2 2
- Studies demonstrate 100% correlation for HER2 results, 85.7% sensitivity for ER, and 80% sensitivity for PR when comparing cell blocks to tissue sections 2
- Both immunohistochemical and biochemical methods are feasible on pleural specimens obtained via thoracentesis or thoracoscopy 3, 4
Clinical Significance of Receptor Conversion
Receptor conversion is common in pleural effusions and has major therapeutic implications:
- ER, PR, and AR status converts in 25-35% of cases between primary tumors and effusion metastases 5
- 19-25% of patients convert from "ER+ or PR+" to ER-/PR-, which would change them from endocrine therapy candidates to non-candidates 5
- HER2 conversion occurs in approximately 6% of cases overall 5, but one study found 63% of metastatic pleural tumors became HER2-positive when the primary was HER2-negative 6
- Prior endocrine therapy increases the likelihood of receptor loss due to evolutionary selection pressure 5
Practical Recommendations
When a breast cancer patient develops malignant pleural effusion:
- Obtain sufficient fluid volume for cell block preparation during thoracentesis or thoracoscopy
- Request ER, PR, and HER2 testing on the cell block using IHC (and FISH for HER2 if IHC is equivocal)
- Use the pleural effusion receptor status to guide systemic therapy decisions, particularly if the primary tumor was tested years ago or after intervening endocrine or anti-HER2 therapy
- Ensure proper fixation protocols are followed per ASCO/CAP guidelines 7
Key Caveats
- Medical thoracoscopy may provide more tissue than simple thoracentesis when adequate cellularity is a concern 3
- Some results may remain indeterminate; final treatment decisions should involve consultation between pathologist and oncologist 1
- The presence of receptor conversion doesn't necessarily indicate assay failure—it often represents true biological evolution of the tumor 5