Fibrolamellar hepatocellular carcinoma (FLHCC) is a rare a rare subtype of hepatocellular carcinoma. The IMbrave150 trial demonstrated that atezolizumab and bevacizumab therapy (ABT) has better treatment outcomes than sorafenib for advanced HCC. However, since patients with known FLHCC were excluded from this trial, the effects of ABT on FLHCC remain unknown. We report the first case of ABT for advanced FLHCC followed by hepatectomy presenting pseudoprogression of lymph node (LN) metastases which was pathologically proven after surgery. The patient was a 30-year-old man with advanced FLHCC and multiple LN metastases behind the pancreatic head, and ABT was introduced. After four courses of treatment, CT indicated a minor decrease in the intratumor vascularity of the liver tumor. However, the size of metastatic LNs increased. Subsequently, the patient presented with bloody stool, and colonoscopy revealed immune-related colitis caused by atezolizumab. Therefore, the fifth course was canceled. A right hemihepatectomy following percutaneous transhepatic portal vein embolization (PTPE) was performed to increase the future liver remnant volume. After PTPE, dynamic CT revealed an objective response to ABT; SD in RECIST 1.1 (7% increase in the LN size and no change of liver tumor), and PR in modified RECIST (47% decrease in the intratumor vascularity of the liver tumor and LNs). Three weeks after PTPE, right hemihepatectomy plus nodal dissection was successfully performed. Pathological findings revealed that approximately 60%–70% of the liver tumor and 70%–80% of the metastatic LNs were necrotic, indicating a good response to ABT. The increasing size of metastatic LNs that occurred during the treatment course was deemed pseudoprogression. Pseudoprogression can be found in patients with solid malignancies treated with immune checkpoint inhibitors, however, rarely occurs in HCC. The first response to metastatic LNs was observed 20 weeks after ABT initiation combined with an increase in nodal volume and a decrease in vascularity. In the updated data of the IMbrave150 trial, 19% of the first responses occurred after week 24. Physicians should consider that ABT may also be effective in FLHCC and may cause pseudoprogression before determining a treatment strategy.

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