VALUTAZIONE DI HER2 NEL CARCINOMA SIEROSO ENDOMETRIALE

BACKGROUND: Uterine serous carcinoma (USC) is an aggressive tumor, responsible for approximately half of endometrial carcinoma-related mortality. A subset of USC shows HER2 overexpression due to ERBB2 amplification, and a recent phase 2 trial demonstrated that these patients benefit from treatment with trastuzumab. Therefore, accurate assessment of HER2 status is critical to properly select patients for targeted therapy. However, previous work has shown a significant intratumoral heterogeneity of ERBB2 amplification in USC and Next Generation Sequencing (NGS) is (and will be) increasingly used in the identification of targetable or clinically relevant (such as POLE point mutations) molecular alterations in endometrial carcinoma. AIMS: To investigate the potential clinical impact of HER2 heterogeneity by examining HER2 status in paired endometrial biopsies, hysterectomy specimens, and metastatic lesions from patients with USC. To investigate the ability of a targeted NGS panel to detect ERBB2 amplification. MATERIALS AND METHODS: Cases of USC were retrospectively identified, for which FFPE tumoral tissue was available (biopsy, hysterectomy, and/or metastasis specimen from the same patient). HER2 expression was assessed by immunohistochemistry (IHC) on all samples and scored using the updated 2018 ASCO/CAP guidelines for testing in breast cancer as negative (0, 1+), equivocal (2+), or positive (3+). All cases which were scored as 2+, those with a discordant status (negative versus positive) between paired samples, and some more were tested by fluorescence in situ hybridization (FISH) for ERBB2 amplification status. A group of cases was also tested by NGS, comparing ERBB2 amplification as measured by NGS, IHC, and ISH. RESULTS: 70 patients resulted eligible for the heterogeneity-part of the project: 45 biopsies, 68 hysterectomies, and 71 metastases (multiple metastatic lesions from the same patient were available in 24 of 42 cases). Using combined IHC/FISH, HER2 positive status was observed in 9 of 68 primary USC (13%). By IHC, paired biopsy and hysterectomy were discordant in 1/43 (2%). Hysterectomy or biopsy and metastasis pairs showed discordance in 8/42 (19%) cases, while multiple metastatic lesions from a same patient in 3/24 (7%). Heterogeneity in HER2 amplification (as defined by Buza) within a single stained slide was present in 4/45 biopsies (9%), 21/68 hysterectomies (31%) and 2/71 metastasis (3%). 93 patients resulted eligible for the second part of the project (NGS). Using combined IHC/FISH, ERBB2 amplification was observed in 8 of 93 cases (9%). NGS identified the same 8 cases with copy number ≥6; all 85 others had copy number <6. CONCLUSIONS: Despite significant HER2 overexpression heterogeneity in over 30% of slides from hysterectomy specimens, there was excellent overall agreement (98%) in HER2 scores between paired biopsy and hysterectomy specimens. However, HER2 overexpression was discordant in 19% of hysterectomy-metastases pairs, suggesting that testing should be performed on a site of metastatic disease prior to the initiation of targeted therapy. In our series, NGS had 100% concordance with combined IHC/FISH in identifying ERBB2 amplification. NGS is highly accurate in detecting ERBB2 amplification in USC and provides an alternative to measurement by IHC and FISH.