If a patient with HER2+ uterine serous carcinoma recurs while on maintenance trastuzumab, would you continue trastuzumab with second line chemotherapy?

I advise against extrapolating data from breast cancer therapies to endometrial cancer. There is no clinical trial supporting the administration of trastuzumab (or other anti-HER2 therapy) with second line chemotherapy after progression on maintenance trastuzumab in serous endometrial cancer. Rather than pivot to a treatment without evidence of efficacy, I advise lenvatinib and pembrolizumab. This combination was granted accelerated FDA approval on 9/17/2019 followed by regular approval on 7/21/21 for patients with non MSI-H advanced endometrial carcinoma. The approval was based on data from KEYNOTE-775, a large phase 3 randomized study of 827 patients with advanced endometrial cancer who had previously received at least one prior platinum-...

Extrapolating from HER2+ (ERBB2-amplified) breast cancer, treatment is a HER2-targeted agent plus cytotoxic chemotherapy. Before we had HER2 tyrosine kinase inhibitors (neratinib, lapatinib, tucatinib) and antibody-drug conjugates (trastuzumab emtansine, trastuzumab deruxtecan) for HER2+ breast cancer, patients were maintained on trastuzumab, and the cytotoxic chemotherapy was changed at the time of progression. There are a wealth of options to choose from for HER2+ breast cancers, but whether or not insurance will find the latest (and very expensive) HER2-targeted therapies based on molecular biology considerations instead of published empirical data is an issue.