Commentary: Case Report: Abdominal Lymph Node Metastases of Parathyroid Carcinoma: Diagnostic Workup, Molecular Diagnosis, and Clinical Management

In the issue of March 2021, Lenschow et al. reported the case of a 46-year-old woman with recurrent, programmed death-ligand-1 (PD-L1) negative, tumor mutational burden (TMB)-high parathyroid carcinoma (PC), who showed stable disease as her best response on imaging, and a three-fold drop in PTH after treatment with intravenous pembrolizumab (1).Parathyroid carcinoma is a rare neuroendocrine tumour, accounting for <1% of all cases of primary hyperparathyroidism (2). While surgery represents the mainstay of treatment for both the primary tumour and metastasis, patients no longer amenable to surgical resection often receive unsatisfactory systemic therapies including cinacalcet, adjuvant radiotherapy, and alkylating agents (3).In recent years, modulation of immune checkpoint proteins expression has been accounted as a prominent mechanism for tumour immune evasion and survival, thus paving the way for new therapeutic approaches (4). Of note, monoclonal antibodies targeting the programmed cell death-1 (PD-1)/PD-L1 and/or the cytotoxic T lymphocyte antigen-4 (CTLA-4)-B7 pathway, hereinafter collectively referred as immune checkpoints inhibitors (ICIs), have shown both clinical effectiveness and a favorable safety profile in patients with advanced solid tumours, and have been included in the treatment repertoire of several malignancies (5).Given the remarkable results obtained by Lenschow et al. with the anti-PD-1 agent pembrolizumab in the above-mentioned case, we performed an extensive search for possible further relevant data sources, including a) full published articles in international online databases (PubMed, Web of Science, Scopus, and Embase); b) preliminary reports in selected international meeting abstract repositories (American Society of Clinical Oncology, ASCO; European Neuroendocrine Tumor Society, ENET; European Society for Medical Oncology, ESMO); c) registered clinical trials in the U.S. National Institutes of Health registry of clinical trials (http://clinicaltrials.gov) and in any primary register of the WHO International Clinical Trials Registry Platform (ICTRP).