Immunotherapy and Anemia: Why Cancer Treatment Can Leave You Feeling Exhausted

Cancer treatment can be physically and emotionally demanding.

But sometimes, one symptom stands out above the rest:

The exhaustion doesn’t improve with rest.

Not ordinary tiredness.
Not the kind of fatigue that follows a busy day.

The kind that makes climbing stairs feel harder.
Makes concentration difficult.
Makes even simple daily tasks feel heavier than usual.

For people undergoing immunotherapy, this kind of fatigue is common—but not always straightforward.

While cancer-related fatigue can have many causes, one important contributor is often overlooked:

Anemia.

Understanding how cancer treatment, blood health, and fatigue intersect can help explain why energy levels may shift—and why those changes matter.

 

What Is Immunotherapy?

Immunotherapy is a type of cancer treatment that helps the body’s immune system recognize and fight cancer cells.

Unlike chemotherapy, which directly targets rapidly dividing cells, immunotherapy works by enhancing or modifying immune responses [1].

Common forms of immunotherapy include:

• Immune checkpoint inhibitors
• CAR T-cell therapy
• Monoclonal antibodies
• Cytokine therapies

These treatments have transformed care for many cancers, including melanoma, lung cancer, lymphoma, and others.

But like all cancer therapies, they can come with side effects—including fatigue.

 

Why Fatigue Is So Common During Cancer Treatment

Cancer-related fatigue is one of the most frequently reported side effects during treatment.

The National Cancer Institute describes cancer-related fatigue as a persistent sense of physical, emotional, or mental exhaustion that is disproportionate to activity and not fully relieved by rest [2].

This fatigue can result from multiple overlapping factors, including:

• The cancer itself
• Immune activation from treatment
• Changes in nutrition or appetite
• Sleep disruption
• Emotional stress
• Changes in blood health, including anemia

Because fatigue is so common, it’s sometimes assumed to be an unavoidable part of treatment.

But understanding why it’s happening matters.

 

The Link Between Immunotherapy and Anemia

Anemia occurs when the body does not have enough healthy red blood cells—or enough hemoglobin—to carry oxygen efficiently.

This can reduce oxygen delivery to tissues, contributing to:

• Persistent fatigue
• Weakness
• Shortness of breath
• Brain fog
• Reduced physical endurance

Cancer treatment can contribute to anemia in several ways.

Some cancers directly affect blood cell production. Inflammation related to cancer or treatment can also interfere with iron metabolism and red blood cell formation [3].

In some cases, immunotherapy-related side effects may contribute indirectly by affecting organ systems involved in blood cell production or increasing inflammatory stress.

While anemia is often discussed more frequently in relation to chemotherapy, it can also be relevant during immunotherapy depending on the treatment type and individual health factors [4].

 

Why Oxygen Delivery Matters

When anemia develops, the issue isn’t just lower blood counts—it’s what that means for the body.

Hemoglobin within red blood cells carries oxygen throughout the body.

When oxygen delivery declines, cells have less fuel for energy production.

That can make symptoms feel much more profound than “just being tired.”

People may notice:

• Increased exhaustion with normal activity
• Difficulty concentrating
• Dizziness or lightheadedness
• Faster heart rate with exertion
• Feeling weaker than expected

Because these symptoms overlap with cancer treatment fatigue, anemia can be easy to miss without appropriate evaluation.

 

Not All Fatigue During Treatment Is the Same

Fatigue during cancer treatment is complex.

Sometimes it reflects:

• Immune system activation
• Medication side effects
• Sleep disruption
• Emotional stress

Other times, blood health may be part of the picture.

That distinction matters because different causes may require different conversations with a healthcare team.

Persistent fatigue, worsening shortness of breath, dizziness, or difficulty with routine activities are worth discussing with a provider.

 

Why Monitoring Changes Over Time Matters

Cancer treatment is dynamic.

Symptoms can shift week to week depending on treatment cycles, nutrition, recovery, hydration, inflammation, and blood health.

This is why awareness of trends matters—not just isolated moments.

Tracking how energy, endurance, and recovery change over time can help people recognize patterns and communicate more effectively with their care team.

 

Looking at Blood Health as Part of the Bigger Picture

Cancer care is complex, and fatigue rarely has a single explanation.

But blood health remains a meaningful part of the conversation.

The Ruby app offers a simple way to monitor blood health trends between healthcare visits. Using fingernail selfie technology, Ruby estimates your Iron Score, which reflects the likelihood of iron-related changes, and your Circulation Score, which reflects how blood is moving through your fingertips.

These insights are not diagnostic and are not intended to replace clinical cancer care—but they may help users better understand broader wellness patterns over time.

Download Ruby on iOS or Android to start tracking today.

As always, if you are undergoing cancer treatment and experiencing fatigue, shortness of breath, dizziness, or worsening symptoms, consult your oncology care team promptly.

 

References

[1] National Cancer Institute. “Immunotherapy to Treat Cancer.”
https://www.cancer.gov/about-cancer/treatment/types/immunotherapy

[2] National Cancer Institute. “Fatigue (PDQ®)–Patient Version.”
https://www.cancer.gov/about-cancer/treatment/side-effects/fatigue/fatigue-pdq 

[3] American Society of Clinical Oncology (Cancer.net). “Anemia and Cancer.”
https://www.cancer.org/cancer/patient-navigation.html 

[4] Cleveland Clinic. “Anemia.”
https://my.clevelandclinic.org/health/diseases/3929-anemia

[5] American Cancer Society. “Managing Cancer-related Fatigue.”
https://www.cancer.org/cancer/managing-cancer/side-effects/fatigue.html