What Kind of Cancer Causes Anemia in Dogs? An In-Depth Look

How cancer can lead to anemia (the three “doors”)

There are three common ways cancer can cause low red blood cells. Picture three doors that all open into the same room—anemia. Your vet’s job is to figure out which door your dog went through:

1. Blood loss. Fast or slow bleeding lowers red blood cells.
   
   

2. Red blood cell destruction. The body breaks down RBCs faster than it can replace them.
   
   

3. Not making enough new cells. The bone marrow falls behind on production.
   
   

We’ll walk through each door, then tie it to the cancers most often involved.

Door 1: Blood loss—bleeding you might not see

Sometimes bleeding is obvious (after an accident). With cancer, bleeding can be hidden inside the belly or the gut. Dogs may suddenly act weak, have very pale gums, or their belly may look swollen. Slow bleeding is trickier—you might only notice darker stools, a picky appetite, or gradual weight loss.

Hemangiosarcoma is the classic bleeder. It’s a cancer of blood vessels that often grows in the spleen, liver, or heart. These tumors are fragile and can rupture, causing internal bleeding and a sudden drop in red blood cells. Dogs can collapse out of the blue. This is a true emergency; a blood transfusion and surgery may be part of the plan.

Not all bleeding is dramatic. Gastrointestinal (GI) tumors and stomach ulcers can ooze small amounts of blood over time. Certain pain medicines (like some NSAIDs) make ulcers more likely. Slow loss like this can lead to iron deficiency anemia—the long, quiet kind that sneaks up on you.

Door 2: Red blood cell destruction—when cells are broken down too fast

This is called hemolytic anemia. It shows up in two main ways:

• Immune-mediated hemolytic anemia (IMHA): the immune system mistakes the dog’s own red blood cells for invaders and destroys them. Cancer can be a trigger for this, as can infections or certain medications. Dogs with IMHA often get weak quickly and may look a bit yellow (jaundiced).
  
  

• Mechanical damage (MAHA): abnormal or turbulent blood flow—sometimes near vascular tumors—can physically tear red blood cells. On a blood smear, the lab may see “shredded” cells called schistocytes.
  
  

Either way, cells are being lost faster than the body can replace them.

Door 3: Not making enough—bone marrow falls behind

Red blood cells are made in the bone marrow. If cancer crowds the marrow or moves into it, the factory slows down. That’s called non-regenerative anemia—there aren’t enough “young” cells (reticulocytes) showing up to replace the old ones. Lymphoma, leukemia, multiple myeloma, and cancers that have spread can all do this. Kidney disease and long-term inflammation can also blunt the marrow’s response, so it’s often a mix of factors in older dogs.

So…what kind of cancer causes anemia in dogs? (The usual suspects)

This is the question we hear most: what kind of cancer causes anemia in dogs? Several can, but these come up again and again:

• Hemangiosarcoma (often sudden bleeding from spleen/liver/heart tumors).
  
  

• Lymphoma (can involve bone marrow or cause “anemia of chronic disease”).
  
  

• Leukemia (starts in blood-forming tissues and directly lowers production).
  
  

• Multiple myeloma (crowds the marrow and can raise blood proteins).
  
  

• GI, spleen, or liver tumors (slow bleeding that’s easy to miss).
  
  

You’ll notice each of these maps back to one of the “doors” above—bleeding, destruction, or reduced production.

Early signs you can actually spot at home

Start with a simple check: look at your dog’s gums. Healthy gums are bubble-gum pink. Pale or white gums are a red flag. Pair that with weakness, quick breathing, a fast heartbeat, or a pot-bellied look, and you should call your vet the same day.

GI bleeding can make stools look dark and tarry. Some dogs vomit or just lose interest in food. None of these prove cancer by themselves, but they’re important pieces of the puzzle.

How your vet figures it out (without the medical maze)

Your vet works step-by-step. It isn’t guesswork—it’s a logical process:

1) History and exam. You’ll go over medications (including over-the-counter pain meds), recent injuries, parasites, and appetite or weight changes. Your vet will check gum color, feel for masses or fluid in the belly, and listen to the heart and lungs.

2) Bloodwork. A CBC confirms anemia and looks at white cells and platelets. PCV shows how low the red cell level is. A blood smear can catch parasites, the clumping seen with IMHA, or those “shredded” cells (schistocytes) from mechanical damage.

3) Regenerative vs. non-regenerative. A reticulocyte count tells whether the bone marrow is trying to fix the anemia. High retics usually mean blood loss or hemolysis (the body is responding). Low retics point toward marrow problems, kidney disease, or long-standing inflammation.

4) Imaging. Ultrasound is great for finding splenic masses, free fluid (blood), liver changes, and GI tumors. X-rays help check chest and abdomen, and CT may be used before surgery or for tougher cases.

5) Extra tests as needed. Coagulation tests (bleeding disorders), fecal occult blood (hidden GI bleeding), urinalysis (kidneys, infections), and, if needed, a bone marrow aspirate/biopsy to look directly at red cell production.

The goal is an accurate diagnosis—because treatment decisions depend on the reason for the anemia.

Treatment: stabilize first, then fix the cause

When anemia is severe, step one is stabilizing your dog. That may include oxygen, IV fluids, and sometimes a blood transfusion to get oxygen levels back up. A transfusion doesn’t cure the problem—it buys time while the team stops bleeding, calms an overactive immune system, or treats cancer.

If there’s a bleeding mass—especially in the spleen—surgery might be the fastest way to stop ongoing blood loss. Dogs with ulcers may get GI protectants, and risky meds may be switched. If parasites are involved, deworming is added. Iron is only used when iron-deficiency anemia is confirmed; giving iron “just because” can be harmful.

When tests support IMHA, vets typically use immunosuppressive medications to stop the immune system from destroying red blood cells. If cancer triggered the immune reaction, treating the tumor is part of the plan.

For cancers that involve blood-forming tissues—lymphoma, leukemia, multiple myeloma—your vet may refer you to an oncologist. Chemotherapy and other targeted treatments are common. Teams adjust drugs and timing to reduce treatment-induced anemia and other side effects, and they monitor counts closely. Some dogs also benefit from palliative radiation or steroids to shrink painful or bleeding tumors.

What you can do at home (small habits that matter)

A few simple routines help a lot:

• Healthy diet & easy rest. Stick with your vet’s nutrition advice and set up a quiet recovery space.
  
  

• Keep a mini journal. Each day, jot down appetite, energy, breathing rate, bathroom habits, and any vomiting/diarrhea. Note the meds you gave. These details help your vet spot trends.
  
  

• Know your dog’s “normal.” Check gum color when your dog is healthy so you’ll recognize a pale change right away.
  
  

If you ever find yourself wondering again what kind of cancer causes anemia in dogs, remember the pattern: bleeding, destruction, or reduced production—and call your vet sooner rather than later.

Where screening fits in

You can’t prevent every case of cancer, but you can aim to catch trouble earlier. Routine vet visits and bloodwork are the backbone. Alongside those, the Oncotect at-home wellness screen for cancer can help flag concerning changes before symptoms get loud. It’s a non-invasive urine test that looks for cancer-associated metabolites. It doesn’t diagnose cancer—that’s your vet’s job—but it can spark earlier conversations and quicker follow-ups when results are concerning.

Screening is especially helpful for seniors and higher-risk breeds like Labrador Retrievers, which face higher odds for certain cancers such as lymphoma and hemangiosarcoma.

→ Learn more or order: Oncotect Cancer Screening Test Kit (oncotect.co)

Bottom line: what to do next

• Check your dog’s gum color. If it’s pale or white—especially with weakness or fast breathing—call your vet today.
  
  

• Expect a step-by-step work-up: CBC/PCV, reticulocyte count, imaging, and sometimes a bone marrow test.
  
  

• Treatment usually starts with stabilizing your dog, then goes after the underlying cause (stop bleeding, calm the immune system, or treat cancer).
  
  

• Keep simple daily notes at home and follow your vet’s plan.
  
  

• Consider adding Oncotect as a proactive screen so you can move sooner if something changes.
  
  

If you're here wondering which types of cancer can cause anemia in dogs, the quick answer is that several different kinds can—and they often behave in recognizable ways. The sooner you get in touch with your vet, the sooner you’ll have a tailored plan for your dog’s needs—and more options to consider to help your furry friend.