Current Laboratory Testing Practices for Assessment of ERBB2/HER2 in Endometrial Serous Carcinoma and Colorectal Carcinoma


 
 Therapy targeted at HER2 (also known as ERBB2) was used initially for breast and gastroesophageal carcinoma and has more recently been adopted for endometrial serous carcinoma (ESC) and colorectal carcinoma (CRC). There is evidence that predictive biomarker testing algorithms for HER2 must be tumor type specific and that an algorithm validated for one tumor type cannot be applied to another.
 
 
 
 To describe current laboratory practices for HER2 assessment in ESC and CRC.
 
 
 
 We surveyed laboratories participating in the 2021 College of American Pathologists (CAP) HER2 immunohistochemistry proficiency testing program.
 
 
 
 The survey was distributed to 1548 laboratories and returned by 1195, of which 83.5% (998) were in the United States. For ESC, 24.0% (287) reported performing in-house testing for HER2 by immunohistochemical staining and/or in situ hybridization; of these, 44.3% (127) performed it reflexively on all cases of ESC. The most common criteria for evaluating HER2 were the American Society of Clinical Oncology/CAP 2018 guidelines for breast carcinoma (69.0%; 194 of 281), whereas only 16.0% (45) used guidelines specific to ESC. For CRC, 20.2% (239 of 1185) performed in-house HER2 testing, and 82.0% of these (196) did the test only at the clinician's request. A plurality (49.4%; 115 of 233) used gastroesophageal cancer guidelines when scoring CRC, 30.0% (70) used the CRC scoring from the HERACLES trial, and 16.3% (38) used the American Society for Clinical Oncology/CAP 2018 guidelines for breast carcinoma.
 
 
 
 Laboratories vary in their approach to HER2 testing in ESC and CRC. Most laboratories did not report using tumor type–specific recommendations for HER2 interpretation. The lack of standardization could present a challenge to evidence-based practice when considering targeted therapy for these diseases.
