Can You Get Cancer From a Blood Transfusion?

Blood transfusions in modern healthcare systems do not transmit cancer from one person to another. A large Scandinavian study tracking over 350,000 transfusion recipients found no excess cancer risk among those who received blood from donors later diagnosed with cancer, even when the donation happened close to the donor’s diagnosis. That said, transfusions do interact with cancer risk in more indirect and surprising ways, from virus transmission that was once a serious problem to immune changes that may affect outcomes for patients already fighting the disease.

Why Cancer Cells in Donated Blood Don’t Take Hold

The fear is intuitive: if a donor unknowingly has cancer, could tumor cells floating in their blood seed a new cancer in the recipient? Circulating tumor cells do exist in the blood of people with cancer, sometimes even before diagnosis. A hypothesis paper has explored this possibility, noting that the sheer volume of transfusions performed worldwide could theoretically expose many recipients to donor-derived tumor cells.

In practice, though, the human immune system is very good at recognizing and destroying foreign cells. A transplanted tumor cell carries surface markers from the donor that look foreign to the recipient’s immune system, triggering rapid rejection. This is why cancer transmission between humans is essentially unheard of outside of organ transplantation, where recipients take powerful drugs specifically designed to suppress immune rejection. Blood transfusion recipients are not immunosuppressed in the same way, and their bodies treat stray donor tumor cells the way they would any foreign tissue.

The strongest epidemiological evidence comes from a Scandinavian cohort study that followed recipients who had received blood from donors diagnosed with cancer within five years of donating. Among the roughly 12,000 recipients exposed to blood from these “precancerous” donors, the adjusted risk of developing cancer was no different from that of recipients whose donors remained cancer-free.

For surgical settings where a patient’s own shed blood is collected and reinfused during cancer operations, irradiation of that blood has been shown to eliminate DNA metabolism in contaminating tumor cells, effectively neutralizing them even if the cells remain technically present.

The Real Historical Danger Was Viruses, Not Tumor Cells

While cancer cells themselves pose virtually no risk, certain cancer-causing viruses were genuinely transmitted through blood transfusions before modern screening existed. Hepatitis C is the most significant example. Before antibody testing became available in the early 1990s, transfusion-transmitted hepatitis C was common and could silently progress through chronic liver disease to liver cancer over decades.

A study of transfusion-associated hepatitis C found that the average time from transfusion to diagnosis of chronic hepatitis was about 10 years, to cirrhosis about 21 years, and to liver cancer about 29 years. Among patients who developed liver cancer linked to hepatitis C, a history of blood transfusion was documented in about 42% of cases.

This historical burden still shows up in modern studies. A large study of women who received transfusions after the year 2000 found that, five or more years after transfusion, there was a small but significant excess risk of liver cancer and non-Hodgkin lymphoma. The liver cancer finding translated to roughly one extra case per 2,300 transfusion recipients over a five-to-nine-year window.

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The researchers noted this may reflect residual hepatitis C transmission during a brief period before nucleic acid testing fully closed the screening gap, or possibly hepatitis B. Today, the risk of receiving blood contaminated with these viruses is vanishingly small, thanks to layered screening that catches infections even before antibodies appear.

How Blood Banks Screen for Dangerous Pathogens

Modern blood safety relies on multiple overlapping defenses. Every donated unit undergoes serological (antibody) testing for HIV, hepatitis B, and hepatitis C. On top of that, nucleic acid testing directly detects viral genetic material, catching infections during the “window period” before antibodies develop. In one large study of nearly 33,000 blood donors, individual-donor nucleic acid testing identified 43 samples that were reactive for HIV, hepatitis C, or hepatitis B despite testing negative on antibody screens, yielding one additional positive detection per 753 donors tested.

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HTLV-1, a virus linked to a rare form of leukemia and lymphoma, is another pathogen screened in many countries. Because HTLV-1 lives inside white blood cells rather than floating freely in plasma, a process called leukoreduction, which filters out the majority of white blood cells from donated blood, likely provides an additional layer of protection beyond antibody screening.

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Human herpesvirus 8, which is involved in the development of Kaposi’s sarcoma, has been demonstrated to transmit through organ transplantation but not through blood transfusion.

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Beyond screening, newer pathogen reduction technologies use photochemical treatments with compounds like amotosalen or riboflavin combined with ultraviolet light to inactivate a broad range of viruses, bacteria, parasites, and residual white blood cells in donated blood components.

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Transfusions and Cancer Recurrence After Surgery

There is a different question that matters far more to people currently being treated for cancer: can receiving a blood transfusion during or after cancer surgery affect whether the cancer comes back? Here the evidence is more unsettling, though the reasons are complicated.

Studies across multiple cancer types have found associations between perioperative blood transfusion and higher rates of recurrence. In a study of over 4,000 colorectal cancer patients, those who received transfusions had a roughly 40% higher adjusted risk of cancer recurrence, regardless of whether they were anemic before surgery.

⁹ A smaller colorectal cancer study found an even stronger association, with the transfused group facing about twice the recurrence risk after adjustment for tumor stage and other factors.¹⁰

Similar patterns appear in head and neck cancer. A study of patients undergoing head and neck cancer surgery found that perioperative red blood cell transfusion was associated with a 37% higher risk of cancer recurrence and a 37% higher risk of death, with a dose-dependent relationship where more units of blood correlated with worse outcomes.

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The critical caveat is that these are observational findings. Patients who need transfusions during surgery tend to have larger tumors, more complex operations, more blood loss, and poorer overall health. Even after statistical adjustments for these factors, residual confounding is hard to rule out. The patients who bleed more during surgery may simply have worse cancers, and the transfusion is a marker of severity rather than a cause of recurrence.

Transfusion-Related Immunomodulation

A phenomenon called transfusion-related immunomodulation, or TRIM, offers a biological explanation for why transfusions might genuinely affect cancer outcomes. When you receive someone else’s blood, your immune system encounters foreign proteins and cellular debris. There is evidence that this exposure can temporarily suppress certain immune functions, which is the same reason transfusions before kidney transplants used to improve graft survival. That immune suppression, beneficial for organ recipients, could theoretically give residual cancer cells a window to establish themselves after surgery.

Research suggests that macrophages, a type of immune cell involved in clearing transfused red blood cells and recycling their iron, may be central to this immunosuppressive effect. The storage of blood products creates a “storage lesion” that generates byproducts which further modulate macrophage behavior in ways that could dampen immune surveillance.

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If TRIM were the main driver, you would expect that removing donor white blood cells from transfused blood (leukoreduction) would eliminate the problem. But the evidence on that front is mixed. Randomized trials comparing buffy-coat-reduced red blood cells, white-blood-cell-reduced products, and autologous blood in colorectal cancer patients found no difference in recurrence rates between these groups.

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A landmark randomized trial took this further by comparing patients who received standard donor blood with those who received their own pre-donated autologous blood. There was no significant difference in cancer recurrence between the two groups. However, both groups had higher recurrence rates than patients who needed no transfusion at all, with recurrence rates roughly doubled in transfused patients regardless of blood source.

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This finding muddies the immunomodulation theory considerably, because autologous blood should not trigger an immune response against foreign cells. It suggests that the need for transfusion itself, rather than exposure to someone else’s blood, may be the real risk factor.

A more recent study in liver cancer patients did find a meaningful difference, with recurrence-free survival averaging about 30 months in the autologous transfusion group versus about 25 months in the donor-blood group.

¹⁵ So the picture is inconsistent across cancer types, and the field has not reached a clean resolution after decades of study.

When Donor White Blood Cells Survive in the Recipient

One of the stranger findings in transfusion biology is that donor white blood cells sometimes persist in the recipient’s body for months or even years, a phenomenon called transfusion-associated microchimerism. In trauma patients who received blood transfusions, long-term microchimerism was observed in a substantial minority. At a median follow-up of over two years, about 15% of patients who received standard blood products and 29% of those who received leukoreduced products showed detectable levels of donor white blood cells, with the donor cells sometimes making up as much as 5% of the recipient’s circulating white blood cells.

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Perhaps more surprising, leukoreduction did not prevent this. A separate study of trauma patients found that 28% of those who received non-leukoreduced blood developed microchimerism versus 37% of those who received leukoreduced blood, a difference that was not statistically significant.

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Microchimerism is not the same as cancer. These surviving donor cells are normal immune cells, and there is no evidence linking transfusion-associated microchimerism to cancer development. But the finding is relevant because it demonstrates that foreign cells from a blood transfusion can persist in the body long-term, which is an important piece of biology to understand when evaluating theoretical risks.

Risks for Severely Immunocompromised Patients

For most transfusion recipients, the immune system easily handles the small number of donor white blood cells that slip through. But for patients whose immune systems are profoundly suppressed, such as those undergoing intensive chemotherapy, the situation can flip dangerously. Instead of the recipient’s immune system attacking the donor cells, the donor’s immune cells can attack the recipient’s tissues. This condition, called transfusion-associated graft-versus-host disease, is rare but often fatal.

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To prevent this, blood products given to heavily immunosuppressed patients are irradiated before transfusion, which destroys the donor lymphocytes’ ability to divide while leaving the red blood cells functional. This is standard practice in oncology wards and bone marrow transplant units. It addresses a real danger, though the danger is from immune attack, not from cancer transmission.

What Happens When a Donor Is Later Diagnosed With Cancer

Blood banks have detailed policies for what happens when a past donor reports a cancer diagnosis. The approach varies by cancer type. A survey of blood collection centers found that donors with a history of solid tumors like carcinomas or sarcomas who had completed treatment were accepted back as donors at about 73% of centers, without further deferral. Donors with a history of blood cancers faced much stricter rules: those with leukemia or lymphoma were permanently deferred at 76% of centers, and those with myelodysplastic or myeloproliferative syndromes were permanently deferred at 86%.

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The stricter approach to blood cancers makes intuitive sense, since these diseases originate in the very cells that circulate in donated blood. But the same survey’s literature review found no documented cases of cancer being transmitted through a blood transfusion. The deferral policies are largely precautionary and vary widely between countries and institutions, reflecting the absence of hard evidence rather than the presence of proven risk.

Cancer That Transmits Naturally Between Individuals

Transmissible cancer does exist in nature, just not in humans. The most studied example is canine transmissible venereal tumor, a cancer in dogs that spreads through direct contact during mating. Genetic analysis has confirmed that this tumor is not caused by a virus; the cancer cell itself is the infectious agent, having originated in a single dog thousands of years ago and spread as a living parasite ever since.

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A similar transmissible cancer has been found in Tasmanian devils, where facial tumors spread through biting. Both cases involve species with limited genetic diversity, which allows the foreign cancer cells to evade immune detection. Humans, by contrast, have high genetic diversity across the population, and our immune systems are exquisitely tuned to reject foreign tissue. This is why cancer transmission between people remains confined to very specific medical situations like organ transplantation with immunosuppression, and has never been convincingly documented through blood transfusion.

CAR-T Therapy and Second Cancers

A newer concern in transfusion-adjacent medicine involves CAR-T cell therapy, where a patient’s own immune cells are genetically modified in a lab and reinfused to fight blood cancers. Reports of second cancers after CAR-T therapy attracted attention starting in 2024. A meta-analysis covering over 5,500 patients treated with CAR-T therapy found that about 5.8% developed a second primary cancer, with blood cancers being the most common type, followed by solid tumors. T-cell malignancies, the specific concern related to the genetic modification process, accounted for only about 1.5% of these second cancers. When trials that directly compared CAR-T against standard chemotherapy were analyzed separately, the rate of second cancers was essentially the same between the two treatments.

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CAR-T therapy is not a blood transfusion in the traditional sense, but it involves reinfusing modified blood cells and raises some of the same conceptual questions about whether introducing altered cells can cause new cancers. The current evidence suggests the second-cancer risk tracks with the underlying disease and prior treatments rather than with the CAR-T product itself, though surveillance is ongoing as more patients reach longer follow-up periods.