A 68-year-old cancer patient developed pernicious anemia—a serious blood condition caused by vitamin B12 deficiency—after receiving atezolizumab immunotherapy for liver and kidney cancer. His immune system began attacking stomach cells needed for vitamin B12 absorption, causing his hemoglobin to drop to 6.1 g/dL. According to Gram Research analysis, vitamin B12 injections improved his condition to 9.5 g/dL, suggesting doctors should monitor B12 levels in patients receiving this immunotherapy drug.
Researchers reported a case of a 68-year-old man who developed a serious type of anemia caused by vitamin B12 deficiency after receiving atezolizumab, an immunotherapy drug used to treat liver and kidney cancer. The patient’s immune system began attacking cells in his stomach that normally help absorb vitamin B12, a condition called pernicious anemia. His blood counts improved after receiving vitamin B12 injections. This case highlights an important but uncommon side effect that doctors should watch for in cancer patients receiving this type of immunotherapy treatment.
Key Statistics
A 2026 case report documented a patient whose hemoglobin dropped to 6.1 g/dL (less than half normal levels) after starting atezolizumab immunotherapy, with recovery to 9.5 g/dL following vitamin B12 injections.
Medical case analysis found that atezolizumab triggered antibodies against gastric parietal cells in one patient, causing autoimmune-induced pernicious anemia with stomach atrophy visible on endoscopy.
According to a 2026 case report, pernicious anemia from immunotherapy drugs remains rarely documented in medical literature, with vitamin B12 deficiency-induced anemia emerging as a potential late-stage complication of checkpoint inhibitor treatment.
The Quick Take
- What they studied: Whether immunotherapy drugs like atezolizumab can cause pernicious anemia, a serious blood condition caused by vitamin B12 deficiency
- Who participated: One 68-year-old man with both liver cancer and kidney cancer who was being treated with atezolizumab-based chemotherapy
- Key finding: The patient developed severe anemia with a hemoglobin level of 6.1 g/dL (normal is 13.5-17.5) caused by his immune system attacking stomach cells needed for vitamin B12 absorption. His condition improved to 9.5 g/dL after receiving vitamin B12 injections.
- What it means for you: If you’re receiving atezolizumab or similar immunotherapy drugs, doctors should monitor your vitamin B12 levels and watch for signs of anemia like fatigue and weakness. This is a rare side effect, but awareness helps catch it early.
The Research Details
This is a case report, which means doctors documented what happened to one specific patient in detail. The 68-year-old man had both liver cancer and kidney cancer and was treated with atezolizumab, a type of immunotherapy drug that works by removing the body’s natural ‘brakes’ on the immune system. After starting treatment, he developed severe anemia—a condition where the blood doesn’t carry enough oxygen because there aren’t enough healthy red blood cells.
Doctors ran blood tests and found his hemoglobin (the protein that carries oxygen) was dangerously low at 6.1 g/dL. They also discovered antibodies attacking his gastric parietal cells—special stomach cells that help absorb vitamin B12 from food. His stomach lining showed signs of atrophy (shrinking and thinning), and his gastrin levels were elevated, all pointing to pernicious anemia caused by vitamin B12 deficiency.
The patient received mecobalamin (a form of vitamin B12) injections, and his hemoglobin improved to 9.5 g/dL. The doctors concluded that the immunotherapy drug had triggered his immune system to attack his own stomach cells, preventing vitamin B12 absorption.
This case is important because pernicious anemia from immunotherapy drugs is rarely reported in medical literature. Understanding that immunotherapy can cause this specific type of anemia helps doctors recognize and treat it faster in other patients. It also shows that doctors need to check vitamin B12 levels in cancer patients receiving these drugs.
This is a single case report, which is the lowest level of scientific evidence. It describes what happened to one patient but cannot prove the drug caused the anemia in everyone who takes it. However, the detailed medical findings (antibody tests, stomach imaging, blood work) support the connection in this case. More research with larger groups of patients would be needed to confirm how common this side effect is.
What the Results Show
The patient presented with severe anemia (hemoglobin of 6.1 g/dL, which is less than half the normal level) after starting atezolizumab treatment. Blood tests revealed signs of hemolysis, meaning his red blood cells were being destroyed. Most importantly, he tested positive for gastric parietal cell antibodies—his immune system was attacking the stomach cells responsible for vitamin B12 absorption.
Upper endoscopy (a camera inserted down the throat to view the stomach) showed atrophic gastritis, meaning the stomach lining had thinned and lost its normal folds. The patient tested negative for H. pylori infection, ruling out a common cause of stomach problems. All evidence pointed to pernicious anemia triggered by the immunotherapy drug.
After receiving mecobalamin (vitamin B12) injections, the patient’s hemoglobin improved to 9.5 g/dL, and the signs of hemolysis resolved. This improvement supported the diagnosis that vitamin B12 deficiency was the root cause of his anemia.
The case revealed that pernicious anemia may develop as a late-stage complication of immunotherapy treatment. The elevated gastrin levels and stomach atrophy suggest that the immunotherapy triggered autoimmune gastritis, a condition where the immune system attacks the stomach lining. This is consistent with how immunotherapy works—by removing immune system ‘brakes,’ it can sometimes cause the immune system to attack the body’s own tissues.
According to Gram Research analysis, pernicious anemia from immunotherapy drugs is rarely documented in medical literature. While doctors recognize that immunotherapy can cause various immune-related side effects (called irAEs), vitamin B12 deficiency-induced anemia is not commonly reported. This case adds to a small but growing body of evidence that immunotherapy drugs can trigger autoimmune conditions affecting the stomach and vitamin absorption.
This is a single case report involving one patient, so we cannot determine how often this side effect occurs or whether it happens in all patients taking atezolizumab. The doctors did not perform a stomach biopsy (tissue sample), so the diagnosis was based on imaging and blood tests rather than direct tissue examination. We don’t know if other patients with similar cancer types and treatments might develop the same condition. Larger studies would be needed to understand the true risk.
The Bottom Line
If you’re receiving atezolizumab or similar immunotherapy drugs: (1) Ask your doctor to monitor your vitamin B12 levels regularly, especially if you develop fatigue or weakness; (2) Report any new symptoms like tiredness, shortness of breath, or tingling in your hands and feet; (3) Discuss with your doctor whether vitamin B12 supplementation might be appropriate as a preventive measure. Confidence level: Moderate—based on one case, but supported by sound medical reasoning.
Cancer patients receiving atezolizumab or other checkpoint inhibitor immunotherapy drugs should be aware of this potential side effect. Doctors treating these patients should consider monitoring vitamin B12 levels, especially in patients who develop anemia or stomach problems. Patients with a family history of autoimmune conditions may be at higher risk. This finding is less relevant to people not receiving immunotherapy.
In this case, pernicious anemia developed after the patient started atezolizumab treatment, suggesting it can emerge weeks to months into therapy. Improvement occurred within weeks of starting vitamin B12 injections. However, individual timelines may vary, and long-term monitoring is important.
Frequently Asked Questions
Can immunotherapy drugs cause vitamin B12 deficiency anemia?
Yes, according to a 2026 case report, atezolizumab immunotherapy triggered pernicious anemia by causing the immune system to attack stomach cells needed for B12 absorption. This is a rare but recognized complication that doctors should monitor for during treatment.
What are the symptoms of pernicious anemia from cancer treatment?
Symptoms include severe fatigue, shortness of breath, dizziness, and tingling in hands and feet. A 2026 case showed hemoglobin dropping to 6.1 g/dL. If you experience these during immunotherapy, contact your doctor immediately for blood work.
How is pernicious anemia from immunotherapy treated?
Vitamin B12 injections (mecobalamin) are the primary treatment. In the documented case, injections improved hemoglobin from 6.1 to 9.5 g/dL. Regular monitoring of B12 levels and hemoglobin is essential during and after immunotherapy treatment.
Should I get vitamin B12 tests while taking atezolizumab?
Yes, doctors should monitor B12 levels regularly during atezolizumab treatment, especially if you develop fatigue or anemia symptoms. A 2026 case report recommends measuring vitamin B12 levels when encountering anemia during immunotherapy.
Is pernicious anemia from immunotherapy common?
No, it’s rare. A 2026 case report notes that vitamin B12 deficiency-induced anemia from immunotherapy is rarely reported in medical literature, though awareness is growing among oncologists treating patients with checkpoint inhibitors.
Want to Apply This Research?
- Track energy levels daily (1-10 scale) and note any new symptoms like shortness of breath, dizziness, or tingling sensations. Log these alongside your immunotherapy treatment dates to identify patterns.
- Set reminders for vitamin B12 supplementation if prescribed, and schedule regular blood work appointments to monitor hemoglobin and B12 levels. Report any new fatigue or weakness to your medical team immediately.
- Create a symptom log within the app tracking: energy level, shortness of breath, dizziness, and tingling. Correlate entries with treatment dates and lab results. Share this log with your oncology team at each visit to catch potential deficiencies early.
This article describes a single case report and should not be considered medical advice. Pernicious anemia from immunotherapy is rare but serious. If you are receiving atezolizumab or similar immunotherapy drugs and develop symptoms like severe fatigue, shortness of breath, or tingling sensations, contact your oncologist or healthcare provider immediately. Do not start or stop any medications without consulting your doctor. This information is for educational purposes and does not replace professional medical evaluation and treatment.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.