Pseudoprogression on treatment with immune-checkpoint inhibitors in patients with gastrointestinal malignancies: Case series and short literature review.

Gastrointestinal cancers are very common cancers with colorectal being the fourth most common type, gastric the sixth, and esophageal the tenth. Although recent advances have been made in management including incorporation of antiangiogenic, anti-EGFR, and anti-HER2 directed therapies, overall their prognosis remains poor. Anti-PD-1 therapy with nivolumab and pembrolizumab are licensed for advanced chemorefractory gastroesophageal cancer and many other checkpoint inhibitor therapies are being assessed alone and in combination in these diseases. One of the challenges posed in assessing response to immunotherapy treatment is the phenomenon of pseudoprogression. This phenomenon, which is well described in patients with malignant melanoma is most frequently described as a size increase of contrast enhancing lesions or appearance of new lesions that stabilize or reduce in size with time. Most other solid tumors have a low incidence of pseudoprogression although cases have been reported for lung, head, and neck cancer and a range of gliomas. Herein we present 6 cases of patients with gastrointestinal cancers who were treated with anti-PD1 (programmed cell death) and anti-PD-L1 (programmed cell death ligand-1) antibodies, and experience pseudoprogression.