Human epidermal growth factor 2 (HER2) amplification in uterine serous carcinoma: an analysis of prognosis and immune microenvironment.

Uterine serous carcinoma (USC) is a biologically aggressive subtype of endometrial cancer. Anti-human epidermal growth factor receptor 2 (HER2) therapy has demonstrated its promising effects on HER2-positive USC. However, data on prognostic relevance and immune microenvironment are limited in HER2-positive USC. This study aimed to determine the clinicopathologic features, prognosis, and the immune microenvironment trait in HER2 status in USC. We applied immunohistochemistry (IHC), fluorescence in situ hybridization (FISH), and multi-color immunofluorescence to investigate HER2 expression and amplification, PD-L1 expression, and tumor infiltration lymphocytes (TIL) in 77 USC (61 pure and 16 mixed-type USC). HER2 IHC 1 + , 2 + , and 3 + were found in 26, 18, and 10 USC, respectively. HER2 staining frequently had an incomplete membrane (basolateral or "U"-shaped) pattern. Twenty-three cases (23/54, 42.6%) showed an intra-tumor heterogeneous staining. HER2 amplification was present in 16/77 (20.8%) USC. HER2 amplification was significantly associated with deep myometrial invasion (> 1/2), and increased intra-epithelial and stromal density of CD20 + or CD8 + TIL (all P < 0.05), but not with USC subtypes (pure versus mixed-type), PD-L1 expression, CD4 + TIL, CD68 + histiocytes, or the CD4 + /CD8 + ratio (p > 0.05). HER2 amplification was associated with poor overall and progression-free survival in USC, but lost the prognostic significance on multivariate analysis. We concluded that HER2 amplified USC had adverse clinical outcomes, but showed the potential active immune microenvironment. Our findings raised the possibility of the combined anti-HER2 and immunotherapy for HER2-positive USC in the future.