Durable partial response to pembrolizumab, lenvatinib, and letrozole in a case of recurrent uterine carcinosarcoma with ESR1 gene amplification.

•ESR1 gene amplification occurs in 7% of uterine carcinosarcoma.•The presence of ESR1 gene amplification in recurrent uterine carcinosarcoma may be targeted by aromatase inhibitors.•ESR1 gene amplification may be identified through immunohistochemical staining for estrogen receptor followed by fluorescence in situ hybridization or tumor targeted gene sequencing.