HER2 gene amplification and protein overexpression in uterine clear cell carcinoma and its implications in targeted immunotherapy.

Abstract

29 Background: Uterine clear cell carcinoma (UCCC) is a high-grade endometrial carcinoma. The current treatment is hysterectomy with post-operative chemotherapy and/or radiation. The 5-year disease free survival remains dismal for UCCC with 65% for early-stage and 54% for advanced stage disease. In addition, UCCC may be more resistant to chemotherapy or radiation therapy than the endometrioid subtype. The aim of the current study is to investigate the HER2 gene amplification status in UCCC and its role for targeted therapy in UCCC. Methods: Twenty-nine cases of UCCC were retrieved from surgical pathology archives of Mayo Clinic at Rochester between 2011 and 2015. All cases except one case were hysterectomy specimens. The blocks contain the most characteristic morphology of UCCC were selected and corresponding paraffin sections were subjected to fluorescent in situ hybridization for amplification of HER2 gene (Hercept, Abbott Molecular) and parallel immunohistochemical (IHC) study. Results: A total of 9 (of 29; 31%) UCCCs showed HER2 amplification and 4 (of 29; 14%) were considered equivocal for HER2 amplification by FISH. A total of 3 (10%) tumors showed 3+ HER2 overexpression while 11 (38%) UCCCs showed 2+ HER2 overexpression, 9 (31%) showed 1+ expression with the remaining cases showing no expression of HER2. Importantly, we observed significant intratumoral heterogeneity with regard to HER2 expression. Comparing the results of IHC with HER2 gene status as determined by FISH, 2 (66%) of the 3 cases that showed 3+ HER2 expression also showed amplification for HER2 by FISH, while 1 (33%) was equivocal for HER2 amplification. Of the 11 tumors that showed 2+ HER2 expression, 6 (55%) were amplified by FISH and 1 (9%) was equivocal. Conclusions: This is the largest number of UCCC cases that has been studied on the HER2 amplification and corresponding protein overexpression. Our results indicate that the HER2 overexpression is common in UCCCs and is frequently associated with HER2 amplification. These results also suggest that targeted adjuvant therapy with trastuzumab-based immunotherapy should be evaluated in patients with UCCC showing HER2 protein overexpression or HER2 gene amplification.