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Pseudoprogression of malignancy in patients treated with systemic immunotherapy is a well- recognised phenomenon and has also been seen in patients treated with combined chemoimmunotherapy. Neoadjuvant chemoimmunotherapy prior to surgery is a relatively new treatment strategy for the management of many malignancies. We report the case of a patient who was suspected to have primary lung squamous cell carcinoma progression following neoadjuvant chemoimmunotherapy. Tissue histopathology from biopsies demonstrated granulomatous sarcoid-like inflammation rather than progression or metastatic disease. The patient proceeded to have successful surgical clearance of residual tumour. Significantly, failure to suspect granulomatous reactions and pseudoprogression has profound influence on the trajectory of patient care, such as, the potential for patients to miss out on curative surgery. In this case report and review of the literature, we evaluate the role of pseudoprogression and the need for radiologists to be aware of this phenomenon so that they do not mistakenly report new metastases and derail the treatment paradigm for patients with curable malignant conditions.

Introduction: The potential of a radioiodine-labeled, anti-adenosine triphosphate synthase monoclonal antibody (ATPS mAb) as a theragnostic agent for simultaneous cancer imaging and treatment was evaluated. Methods: Adenosine triphosphate synthase monoclonal antibody was labeled with radioiodine, then radiotracer uptake was measured in 6 different cancer cell lines. In vivo biodistribution was evaluated 24 and 48 hours after intravenous injection of 125 I-ATPS mAb into MKN-45 tumor-bearing mice (n = 3). For radioimmunotherapy, 18.5 MBq 131 I-ATPS mAb (n = 7), isotype immunoglobulin G (IgG) (n = 6), and vehicle (n = 6) were injected into MKN-45 tumor-bearing mice for 4 weeks, and tumor volume and percentage of tumor growth inhibition (TGI) were compared each week. Results: MKN-45 cells showed the highest in vitro cellular binding after 4 hours (0.00324 ± 0.00013%/μg), which was significantly inhibited by unlabeled ATPS mAb at concentrations of greater than 0.4 μM. The in vitro retention rate of 125 I-ATPS mAb in MKN-45 cells was 64.1% ± 1.0% at 60 minutes. The highest tumor uptake of 125 I-ATPS mAb in MKN-45 tumor-bearing mice was achieved 24 hours after injection (6.26% ± 0.47% injected dose [ID]/g), whereas tumor to muscle and tumor to blood ratios peaked at 48 hours. The 24-hour tumor uptake decreased to 3.43% ± 0.85% ID/g by blocking with unlabeled ATPS mAb. After 4 weeks of treatment, mice receiving 131 I-ATPS mAb had significantly smaller tumors (679.4 ± 232.3 mm 3 ) compared with control (1687.6 ± 420.4 mm 3 , P = .0431) and IgG-treated mice (2870.2 ± 484.1 mm 3 , P = .0010). The percentage of TGI of 131 I-ATPS mAb was greater than 50% during the entire study period (range: 53.7%-75.9%). Conclusion: The specific binding and antitumor effects of radioiodinated ATPS mAb were confirmed in in vitro and in vivo models of stomach cancer.