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.

Purpose

B cells play a key role in outcomes of cancer patients and responses to checkpoint blockade immunotherapies. However, the effect of radiation therapy on B cell populations is poorly understood. Here we characterize the effects of radiation on the development, survival, and phenotype of physiological B-cell subsets.

Methods and materials

Naïve and immunized tumor bearing and nontumor bearing mice were treated with large-field or focal stereotactic radiation and distinct B-cell subsets of varying developmental stages were analyzed by flow cytometry and real-time reverse transcription polymerase chain reaction.

Results

We first report that focal stereotactic radiation is highly superior to large-field radiation at inducing tumor infiltration of B cells, CD8⁺ T cells, and macrophages. We observed that radiation affects B cell development in the bone marrow, increasing frequencies of early pro-B cells and late pro-B cells while inducing upregulation of programmed cell death protein 1. We then demonstrate that class switched B cells and plasma cells are highly resistant to radiation therapy compared with naïve B cells and upregulate activation markers programmed cell death 1 ligand 2 and major histocompatibility complex class II) after radiation. Mechanistically, radiation upregulates Xbp1 and Bcl6 in plasma cells, conferring radioresistance. Furthermore, using an immunization approach, we demonstrate that radiation enhances activation-induced cytidine deaminase mediated class switching and somatic hypermutation in primed B cells.

Conclusions

These data demonstrate that stereotactic radiation is superior to large-field radiation at inducing infiltration of immune cells into tumors and that plasma cells and class switched B cells are highly resistant to radiation therapy. These results represent the most comprehensive analysis of the effects of radiation on B cells to date and identify novel mechanisms by which radiation modulates immune cells within the tumor microenvironment.