Human epidermal growth factor receptor 2 (Her2) testing for uterine serous carcinoma: Report of scenarios of unusual overexpression.

The human epidermal growth factor receptor 2 (Her2) is tested in many human cancers, including breast, bladder, pancreatic, ovarian and stomach. The American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) have issued Clinical Practice Guidelines for reporting Her2 results for breast carcinomas (Wolf et al., 2018). For the last 1-2 years Her2/neu is tested in endometrial serous carcinoma, especially in recurrent tumors or non-responsive tumors as an option for additional treatment. College of American Pathologists (CAP) offers a template for prognostic marker reporting results for specimens with endometrial carcinomas (Fitzgibbons et al., 2019). Her2/neu testing by immunohistochemistry (IHC) mandates rigorous fixation time control, e.g., fixation time should fall within 6-72 h (Recommendations for Her2 Testing in Breast Cancer, 2013). For that reason, in breast cancers, Her2/neu testing is done on initial core biopsy specimens. The test is however, repeated on excision specimen in high grade tumors where Her2/neu expression was initially negative on core biopsies. For endometrial serous carcinoma no guidelines have been set or proposed as of yet. The Gynecologic Oncologists request this test because of proven benefit of adding Trastuzumab (Fader et al., 2018) and that is why it is important to documenting the findings in this report in the literature so that an informed request can be made by the treating oncologist when multiple tissue samples from the same patient are available for testing. Similarly pathologists also can decide which would be the best sample to test when no instruction is received. We report here three separate scenarios of uterine serous carcinomas in which the Her2/neu expressions were unique enough to justify documentation and therefore have implications for determining which specimen is ideal for the Her2 overexpression testing and likely to have highest possibility in identifying the Her2/neu overexpressed clone in the tumor which would expand the therapeutic options for the patients.