A Case of Pernicious Anemia Induced by Atezolizumab in Hepatocellular Carcinoma and Renal Cell Carcinoma

Introduction

Vitamin B12 (Vit.B12; cobalamin) is an essential element for DNA synthesis in red blood cells (RBCs). Pernicious anemia (PA) is a type of megaloblastic anemia triggered by a deficiency of Vit.B12 or folic acid. Vit.B12 loss is caused by the interruption of Vit.B12 absorption due to gastric parietal cell dysfunction. Normally, parietal cells generate intrinsic factor, which plays a crucial role in Vit.B12 absorption in the terminal ileum. Parietal cells are destroyed by the developed parietal cell antibodies, leading to the loss of Vit.B12 in the body. Here, we present a case of double carcinoma (hepatocellular carcinoma [HCC] and renal cell carcinoma [RCC]) that developed PA after treatment with atezolizumab-containing regimen. PA was induced by parietal cell antibodies produced after atezolizumab administration.

Case Report

A 68-year-old man visited our hospital with general fatigue and appetite loss in July 2023. An abdominal computed tomography (CT) scan detected multiple intrahepatic nodules, a right adrenal gland nodule, a para-aortic lymphadenopathy, and a right renal tumor. He underwent a liver biopsy, which revealed HCC. Further, the right renal tumor was clinically diagnosed as clear cell RCC based on the findings of a contrast-enhanced CT scan in September 2023 (Figure 1A, 1B). Metastatic lesions were indicated in the right adrenal gland and para-aortic lymph nodes; however, the primary carcinoma (HCC or RCC) that invaded these sites at that time remains unknown. HCC was considered the therapeutic priority; thus, the patient was initially scheduled to receive 4 cycles of atezolizumab–bevacizumab (Atezo–Bev) therapy from November 2023. Hypothyroidism occurred as an immune-related adverse event (irAE) in January 2024 when he underwent 2 cycles of Atezo–Bev therapy. Atezo–Bev therapy was continued for 4 cycles, and levothyroxine at 25 μg/day was initiated, following the gradual ramp-up to 100 μg/day. The evaluation with contrast-enhanced CT scan in April 2024 demonstrated that the liver tumor exhibited a significant size reduction, although the renal tumor remained unchanged in size, indicating that the anti-tumor effect was limited to HCC (Figure 1C). Consequently, Atezo–Bev therapy was discontinued, and levothyroxine was increased to 150 μg/day to manage thyroid function. In May 2024, the patient was switched to cabozantinib (60 mg/day), targeted for second-line therapy for HCC and size-unchanged RCC. Following the introduction of cabozantinib, he developed thrombocytopenia that required a gradual dose tapering to 20 mg/day in July 2024. The hemoglobin (Hb) level (9.9 g/dL) has decreased regardless of continuous cabozantinib administration at the reduced dose of 20 mg/day in February 2025, when cabozantinib was continued. He was admitted to our hospital with an emerging anemic symptom in April 2025.

He reported a medical history of hypertension and type 2 diabetes mellitus. His familial medical history revealed colon cancer in his brother. He demonstrated no allergic tendency to drugs, nor medically significant alcohol drinking or smoking. His performance status was 1. Physical examination revealed stable vital signs except for mild tachycardia (95 bpm). He presented with generalized pallor, including anemic conjunctiva, abdominal distension, and lower extremity edema.

Blood count test revealed Hb of 6.1 g/dL; mean corpuscular volume of 116 fL, indicating macrocytic anemia; platelet count of 5.8×104/μL. Serological testing demonstrated the following abnormalities: lactate dehydrogenase (LD) at 369 IU/L (normal range, 119–229) with a high percentage of LD1 and LD2 isozymes; indirect bilirubin of 1.15 mg/dl, and haptoglobin of <10 mg/dL, indicating a hemolytic pattern. The Vit.B12 levels were below the lower sensitivity level (<148 pg/mL). Gastric parietal cell antibodies were positive (×20), whereas intrinsic factor antibodies were negative. The gastrin levels were increased at 300 pg/mL (normal range, 11.9–46.9). He tested negative for Helicobacter pylori antibodies (Table 1). Upper gastrointestinal endoscopy demonstrated no evidence of massive bleeding associated with the decrease in Hb levels, and showed atrophic mucosa that affected almost the entire stomach, including the fornix, body, and antrum areas. The loss of gastric folds and marked vascular visibility were observed (Figure 2A–2D). These findings were consistent with atrophic gastritis. We defined it as open type (O-3) atrophic gastritis according to the endoscopic Kimura–Takemoto classification [1]; however, we did not perform gastric mucosa biopsy. Colonoscopy up to the ileocecal region detected neither bleeding nor a neoplastic lesion. Bone marrow aspiration revealed megaloblastic change in erythroblast (Figure 1E). A follow-up contrast-enhanced abdominal CT scan demonstrated a controlled HCC portion, but RCC remained stable in size, and the right adrenal tumor had enlarged (Figure 1D). Concurrently, the right adrenal tumor was diagnosed as a metastatic lesion from RCC. Based on these findings, the anemia was considered megaloblastic anemia induced by Vit.B12 deficiency (PA).

Figure 3 illustrates the clinical course. The patient received 6 units of RBC transfusion within 3 days of admission. Mecobalamin was injected intramuscularly thrice per week for the first 3 weeks, followed by oral intake of mecobalamin. To prevent iron insufficiency during recovery, sodium ferrous citrate (100 mg/day) was administered from days 4 to 21. After this treatment intervention, the Hb levels gradually improved to approximately 9.5 g/dL without further RBC transfusions, despite not reaching the normal range. Haptoglobin levels normalized, and LD levels reduced to the normal range, indicating the resolution of RBC destruction. We found that the anemia was partially triggered by PA, and anemia of chronic disease (ACD) derived from persistent cancerous conditions coexists. The patient resumed cabozantinib on day 23; however, intensive therapy was discontinued 2 months after admission, and the treatment plan was switched to best supportive care.

Discussion

This was a case of PA triggered by Vit.B12 deficiency, which was associated with atezolizumab-induced irAE. The anemia at admission was manifested with a hemolytic pattern, with the findings of Vit.B12 deficiency, hypergastrinemia, and the presence of parietal cell antibody. Atrophic gastritis was observed in the entire stomach. This anemia was suspected due to PA based on these findings. Further, after mecobalamin administration, anemia was improved with the resolution of RBC destruction, which proved a causal relationship between Vit.B12 deficiency and PA. Therefore, we identified that the anemia was partially caused by PA, and ACD might coexist. During the clinical course, he received cabozantinib, which is a multiple tyrosine kinase inhibitor (TKI), including MET and VEGF receptors, indicated for HCC and RCC. Before this treatment, atezolizumab had been administered. Regarding the association of TKI with anemia from Vit.B12 deficiency, sunitinib-related macrocytosis [2] or erlotinib-related megaloblastic anemia [3] has been reported, although no report indicated that cabozantinib was related to Vit.B12 deficiency. A hypothesis indicated that sunitinib-induced macrocytosis, which is mostly documented among TKI-related anemia, may be derived from c-Kit inhibition via the off-target effect of sunitinib [4]. Hence, no obvious evidence for the activation of immune-related systems as the cause of TKI-related anemia has been proven. Conversely, the PA in our study demonstrated the production of parietal cell antibody and the findings of autoimmune gastritis (AIG), which may be derived from the activated conditions of autoreactive CD4+ T lymphocytes. The removal of immune checkpoint brakes by atezolizumab may promote this pathogenesis. Further, PA occurred due to the immune checkpoint inhibitor (ICI)-related effect, which may take 1 or 2 years or even longer to see noticeable findings, as PA might emerge as a later stage of AIG [5]. IrAEs manifest not only during or immediately after treatment but also late-onset from treatment initiation [6,7]. Therefore, we considered atezolizumab to be the most likely cause of this PA. Our patient had already developed hypothyroidism as an irAE before the onset of anemia; thus, PA appeared as a second irAE in the clinical course. Notably, thrombocytopenia improved after Vit.B12 administration, suggesting that it was a manifestation of Vit.B12 deficiency along with PA.

Recently, ICIs have been widely administered in cancer chemotherapy, either as monotherapy or in combination with other drugs, including cytotoxic drugs or kinase inhibitors. When anemia appears during treatment, the underlying cause needs to be identified. However, cytotoxic drugs or kinase inhibitors can cause anemia; thus, it is challenging to determine whether an ICI contributes to anemic conditions in a combination therapy setting. Anemia derived from ICI is recognized as a systemic irAE [8]. Generally, common hematologic irAEs include autoimmune hemolytic anemia, aplastic anemia, pure red cell aplasia, hemophagocytic lymphohistiocytosis, and bone marrow failure syndromes [9,10]. Conversely, only a few studies focused PA [11] or megaloblastic anemia induced by Vit.B12 deficiency [12] after ICI treatment. However, additional reports exist in cases with autoimmune encephalitis, in which glutamic acid decarboxylase 65 (GAD 65) antibody is identified after ICI treatment [13,14]. GAD 65 antibody is popularly associated with PA [15]; thus, the immune activation of ICI treatment is thought to lead to PA. In this context, El-Refai SM et al reported that the frequency of PA among all autoimmune diseases under ICI treatment for lung and renal cancer were 5.4% and 3.7%, respectively. These data indicate that PA might be more frequent than autoimmune hemolytic anemia (0.3% for each cancer type) [16]. The discrepancy in PA frequency across studies may originate from differences in databases and a potentiality of low clinical awareness regarding PA under ICI treatment. Further, PA is recognized as the progressive status of AIG, in which not all patients with AIG progress to PA [5,17]. ICI treatment-induced PA is suggested to emerge at the late phase compared with other ICI-related adverse effects. Therefore, we recommend the inclusion of PA in the differential diagnosis of anemia during and after ICI treatment.

The following process has been proposed regarding the mechanism of Vit.B12 deficiency-PA during ICI treatment. The existence of parietal cell antibodies or intrinsic factor antibodies targets parietal cells via H+/K+ ATPase. Inflammatory cells (T lymphocytes, B lymphocytes, and macrophages) infiltrate the gastric mucosa and destroy parietal cells and chief cells through apoptosis. This leads to intestinal metaplasia, gastric mucosa atrophy, intrinsic factor deficiency, and a decrease in hydrochloric acid production [8]. The severity of these findings may differ by case, as ICI treatment-induced PA may progress more rapidly than traditional PA.

PA can be related to gastritis during ICI treatment for the above reason. When PA occurs with the manifestation of gastritis, a differential diagnosis for gastritis may be required. Gastritis frequently observed with ICI administration includes immune-related gastritis, H. pylori gastritis, or cytomegalovirus gastritis, and AIG. Discrimination between immune-related gastritis and AIG is particularly important. The feature of immune-related gastritis manifests as lymphocytic infiltration and crypt abscesses in the gastric mucosa, and positron emission tomography-CT can be a useful diagnostic tool. Conversely, PA-related AIG is characterized by low Vit.B12 levels [18]. Therefore, measuring Vit.B12 levels is essential when encountering cases of anemia and gastritis during ICI treatment.

This study has limitations. Serum Vit.B12 levels could not be measured before the induction of ICI treatment, leading to difficulty in defining the exact time of occurring Vit.B12 deficiency. The histopathological examination for gastric tissue was not performed, which hindered the pathological diagnosis of AIG.

Conclusions

We report a case of PA during atezolizumab treatment for HCC. PA should be considered a potential cause of anemia during ICI-based treatment. Measuring Vit.B12 levels is essential when encountering cases of anemia and gastritis during ICI treatment.