Exceptional Response to Nivolumab and Stereotactic Body Radiation Therapy (SBRT) in Neuroendocrine Cervical Carcinoma with High Tumor Mutational Burden: Management Considerations from the Center For Personalized Cancer Therapy at UC San Diego Moores Cancer Center

Neuroendocrine carcinoma of the cervix is an ultra‐rare malignancy with a poor prognosis and limited treatment options. Checkpoint blockade immunotherapy has rapidly developed into an emerging standard of care for several common disease types. Interestingly, in preclinical and retrospective clinical data, radiation therapy has been demonstrated to synergize with checkpoint inhibitors. Here we report a patient with metastatic, chemotherapy‐refractory neuroendocrine carcinoma who presented with partial bowel obstruction due to a large tumor burden. Genomic analysis demonstrated a high number of alterations on liquid biopsy (circulating tumor DNA [ctDNA]), which prompted treatment with stereotactic body radiation therapy (SBRT) combined with anti‐programmed cell death protein 1 antibody. Tissue rebiopsy and comprehensive genomic profiling confirmed high tumor mutational burden and a mismatch repair gene defect. The patient manifested near‐complete systemic resolution of disease, ongoing at 10+ months. We discuss the novel treatment modality of SBRT combined with a checkpoint inhibitor and the implications of molecular profiling and tumor mutational burden as potential predictors of response. KEY POINTS. High‐grade, large‐cell neuroendocrine carcinoma of the cervix is an ultra‐rare malignancy that carries a grim prognosis. Next‐generation sequencing may reveal key mutations in MSH2 genes amongst others. MSH2 mutations target the DNA mismatch repair process and can predispose patients to malignancies with high mutational burdens. Immunotherapy combined with radiation therapy can elicit a significant response, both within and outside the field of radiation. The latter is termed the “abscopal” effect, perhaps mediated by radiation‐induced cross presentation of tumor antigens resulting in immune activation. Sequencing of blood‐derived ctDNA showed a high number of alterations, and tissue sequencing confirmed a high tumor mutational burden as a consequence of a mismatch repair gene defect. This observation led to a therapeutic “match” with an anti‐ programmed cell death protein 1 antibody combined with SBRT, resulting in a durable (10+ months), near‐complete remission in a patient with advanced chemotherapy‐refractory disease.