Risk of tumor flare after nivolumab treatment in patients with irradiated field recurrence.

Nivolumab offers a statistically superior survival benefit over docetaxel in patients with advanced, previously treated squamous and non-squamous non-small-cell lung cancer (NSCLC). However, we unexpectedly encountered "tumor flare" that was associated with initially increased tumor lesion size and subsequently decreased tumor burden in patients with NSCLC treated with nivolumab, which is known as pseudoprogression. Tumor flare with rapid progression related to accelerated progression after nivolumab treatment has also been observed. Here we report two patients having early irradiated field recurrence who experienced "tumor flare" that showed pseudoprogression and rapid progression. In addition, we present a brief literature review on "tumor flare" after nivolumab treatment.