A Rare Delayed Atypical Pseudoprogression inNivolumab-Treated Non-Small-Cell Lung Cancer

Immune checkpoint inhibitors such as Nivolumab work by preventing the inactivation of host T-cells by tumour cells, therebyallowing the T-cells to attack the tumour cells, which results in tumour tissue necrosis. We describe a 78-year-old woman withmetastatic lung adenocarcinoma treated with Nivolumab after disease progression followingfirst-line chemotherapy. Computedtomography (CT) after 3 cycles showed a smaller left lower lobe (LLL) primary and stable right lower lobe (RLL) metastaticlesion. CT after 9 cycles showed a reduced RLL mass and an increase in LLL primary. However, CT after 15 cycles showed thatthe RLL mass had further reduced in size but the LLL mass was significantly larger. The biopsy of the LLL lesion showednecrotic areas and reactive inflammatory changes, without residual malignancy. A repeat CT after further 4 cycles confirmedtumour regression in both the primary and the metastatic lesions. There was a prior reported case of pseudoprogression in anon-small-cell lung cancer patient who had 7 cycles of Nivolumab, and it was diagnosed during a further line of chemotherapy.Here, we report a patient with pseudoprogression during treatment with Nivolumab and at a much later time, after 15 cycles