How Does Leukemia Affect the Lymphatic System?

Leukemia disrupts the lymphatic system in several overlapping ways: cancerous white blood cells physically accumulate in lymph nodes and the spleen, hijack the chemical signals that normally guide immune-cell traffic, block the flow of lymphatic fluid, and suppress the immune defenses the lymphatic system is supposed to provide. The specific pattern depends heavily on the type of leukemia involved, but the lymphatic system is rarely spared in any form of the disease. What looks like “swollen glands” on the outside reflects a deeper takeover that reaches from the architecture of individual lymph nodes to the body’s ability to fight off ordinary infections.

How Leukemia Cells Find Their Way Into Lymph Nodes

Healthy immune cells constantly circulate between the bloodstream and lymph nodes, guided by molecular “address labels” called chemokine receptors on their surfaces and matching signals produced by lymph node tissue. Leukemia cells exploit this same system. In chronic lymphocytic leukemia (CLL), the most common adult leukemia, the malignant B cells carry unusually high levels of the receptors CCR7, CXCR4, and CXCR5, which are the main receptors responsible for steering B cells into lymph nodes and positioning them within particular zones once they arrive.¹ Because the leukemia cells overexpress these homing receptors, they flood into lymph nodes far more aggressively than normal cells would.

This is not just a laboratory curiosity. Research comparing CLL cells in the blood with those already lodged in lymph nodes found that the circulating cells had significantly higher expression of CXCR4 and CCR7 than the cells already inside the nodes, suggesting that the cells most “eager” to migrate are constantly being funneled toward lymphoid tissue.² The responsiveness of CLL cells to CCR7 signals has even been correlated with the degree of clinical lymphadenopathy, meaning that patients whose leukemia cells respond most strongly to these homing cues tend to have the most widespread lymph node enlargement.¹

What Happens to Lymph Nodes and the Spleen

Once leukemia cells settle in lymph nodes, the nodes swell, sometimes dramatically. CT imaging studies of leukemia patients with abdominal and pelvic lymph node involvement show that the pattern of enlargement varies by subtype. In CLL, about 96% of enlarged abdominal lymph nodes were conglomerated, meaning multiple nodes had matted together into large masses. By contrast, in acute myeloid leukemia (AML) only about half the enlarged nodes were conglomerated, and in acute lymphocytic leukemia (ALL) the figure was similar at roughly 56%. CLL nodes also tended to be physically larger than those seen in the acute leukemias.³ Most of the enlarged nodes looked uniform on imaging, though about one in five showed a mixed appearance with a distinct rim.

The spleen is arguably the body’s largest lymphoid organ, and it takes a hit too. In the spleen’s red pulp, specialized cords normally filter out old or damaged red blood cells. When leukemic cells accumulate in these cords, they cause chronic distention and contribute to splenomegaly, the clinical term for an abnormally enlarged spleen.⁴ Patients often feel this as a sense of fullness or discomfort under the left rib cage, and a markedly enlarged spleen can crowd other organs, reduce appetite, and occasionally rupture.

When Lymphatic Fluid Flow Gets Blocked

The lymphatic system is not just a collection of immune outposts. It is also a plumbing network, carrying lipid-rich fluid called lymph (and, in the gut, a milky fat-laden fluid called chyle) through ducts and back toward the bloodstream. Leukemia can physically obstruct that plumbing. In CLL, buildup of leukemic cells in and around the thoracic duct, the body’s main lymphatic drainage channel, can cause chylothorax: a condition where lymphatic fluid leaks into the pleural space around the lungs.⁵ The suspected mechanism is “sludging” of lymph, where the sheer volume of leukemic cells slows lymphatic drainage to the point that fluid backs up and seeps out.

Chylothorax from CLL is rare, but when it happens it can be stubborn. One reported case involved a 93-year-old woman with CLL who developed recurrent pleural effusions that kept returning despite eight separate drainage procedures. She ultimately required surgery to tie off the thoracic duct region and seal the pleural surfaces to stop the fluid from re-accumulating.⁶ While bilateral chylothorax from CLL is uncommon enough to be reported as individual case studies, it illustrates a broader principle: any leukemia that massively infiltrates lymph nodes has the potential to compromise lymphatic flow in whatever body region those nodes drain.

How the Immune System Breaks Down

Lymph nodes are where much of the body’s adaptive immune response gets organized. T cells meet antigen-presenting cells there, B cells mature and produce antibodies, and the whole system coordinates its response to infections. When leukemia cells colonize this space, they do not just sit passively. CLL cells within lymph nodes express immune-suppression genes that appear to interfere with how antigen-presenting cells and T cells behave, effectively dampening the anti-tumor immune response and, as collateral damage, weakening defenses against everyday pathogens.⁷

The result is that CLL patients are highly susceptible to infections, and those infections are a leading cause of illness and death in the disease. The immune defects are both built into the disease and worsened by treatment. The single most important immune failure in CLL is hypogammaglobulinemia, a drop in antibody levels that becomes more severe as the disease progresses. Because antibodies are the primary defense against bacteria, this deficit leaves patients vulnerable to serious bacterial infections in particular.⁸ Many CLL patients eventually receive immunoglobulin replacement therapy for this reason. The immune suppression extends beyond antibodies to cellular immunity as well, opening the door to viral and fungal infections that healthy individuals would easily control.

Differences Across Leukemia Subtypes

Not every leukemia engages the lymphatic system in the same way, and the differences matter clinically.

CLL, as described above, is the leukemia with the most prominent and consistent lymph node involvement. Within CLL, pathologists distinguish between “non-accelerated” and “accelerated” disease based on what the lymph nodes look like under the microscope. Accelerated CLL features expanded proliferation centers within the nodes and a high rate of cell division. This distinction carries real prognostic weight: median survival from biopsy was about 76 months for non-accelerated CLL, dropped to 34 months for accelerated CLL, and fell to only about 4 months in cases that had transformed into diffuse large B-cell lymphoma, a far more aggressive cancer.⁹

Acute leukemias affect the lymphatic system differently. Precursor T-cell lymphoblastic lymphoma, a disease closely related to T-cell ALL, frequently produces bulky masses in the mediastinum, the central compartment of the chest. Up to 70% of patients develop anterior mediastinal masses, often accompanied by massive pleural and pericardial effusions. These masses can obstruct major blood vessels and airways, leading to complications like superior vena cava syndrome and tracheal compression. While the bone marrow may be spared initially, about 60% of patients eventually develop marrow infiltration as the disease progresses.¹⁰

Acute myeloid leukemia (AML) is generally thought of as a bone marrow disease, but it can also form solid tumors in lymph nodes and other sites outside the marrow. These tumors, called myeloid sarcomas, occur in roughly 3 to 5% of AML cases and can appear in lymph nodes, soft tissue, bone, the central nervous system, and various organs.¹¹ Their presence in a lymph node can sometimes cause diagnostic confusion, since they can mimic lymphoma on initial biopsy.

Damage to the Gut’s Lymphoid Tissue

The lymphatic system extends deep into the intestinal wall. Gut-associated lymphoid tissue (GALT) includes clusters of immune cells in the intestinal lining and the underlying tissue layer, and it serves as a critical barrier preventing bacteria from crossing from the gut lumen into the bloodstream. In animal models of acute lymphocytic leukemia, researchers found significant structural damage to this barrier. The number of lymphoid cells in both the intestinal lining and the tissue just beneath it dropped sharply compared to healthy controls.¹² With fewer immune cells guarding the intestinal wall, bacteria can more easily slip through into the body, a process called bacterial translocation. For leukemia patients who are already immunocompromised, this translocation can seed dangerous bloodstream infections that seem to come out of nowhere.

Adults Versus Children

Acute lymphocytic leukemia is the most common cancer in children, and it also occurs in adults, but the way it interacts with the lymphatic system differs between the two age groups. Researchers have examined enzymes called matrix metalloproteinases (MMP-2 and MMP-9) that help cells break through tissue barriers, essentially enabling leukemia cells to escape the bone marrow and invade other sites. In adults with ALL, about 65% of cases showed detectable levels of one or both enzymes, and MMP-2 in particular was statistically linked to the appearance of extramedullary infiltrates, meaning leukemia deposits outside the bone marrow, including in lymph nodes and other organs. In pediatric ALL, by contrast, only about 13% of cases showed detectable metalloproteinase expression, and there was no statistical link to extramedullary disease.¹³ The implication is that adult ALL may have a greater inherent capacity to spread into lymph nodes and other tissues outside the marrow, which partly explains why adult ALL is generally harder to cure than the childhood version.

How Lymphatic Involvement Shapes Diagnosis and Monitoring

Because leukemia so often involves the lymphatic system, imaging of lymph nodes plays an important role in staging and monitoring the disease. PET/CT scanning, which detects areas of abnormally high metabolic activity, has become particularly useful. In leukemia, PET/CT contributes to identifying extramedullary infiltration (leukemia deposits outside the marrow), monitoring for relapse, and detecting Richter’s transformation, the dangerous conversion of indolent CLL into aggressive large-cell lymphoma.¹⁴ In adult T-cell leukemia, PET/CT findings have been shown to be useful for clinical grading of the disease, helping distinguish indolent from aggressive forms.¹⁵

For CLL in particular, the size, distribution, and internal appearance of lymph nodes on CT are part of the staging criteria. The distinction between a patient with a few mildly enlarged nodes and one with massive conglomerate lymphadenopathy across multiple body regions carries direct implications for prognosis and treatment urgency. Richter’s transformation is especially important to catch early, because the prognosis drops precipitously once it occurs, and a rapidly growing or intensely FDG-avid node on PET/CT is one of the earliest signals that the transformation may be underway.

How Treatment Interacts with the Lymphatic System

Some of the newer targeted therapies for leukemia work precisely by disrupting the relationship between leukemia cells and the lymph node microenvironment. Ibrutinib, a widely used drug for CLL, blocks a signaling pathway that leukemia cells rely on to stay anchored within lymph nodes. When patients start ibrutinib, most experience a transient spike in their circulating lymphocyte count, which looks alarming on a blood test but actually reflects leukemia cells being flushed out of the lymph nodes and into the bloodstream, where they are more vulnerable to dying off.¹⁶ Lymph nodes typically shrink during this process even as blood counts temporarily rise. Patients and even some clinicians unfamiliar with the drug’s mechanism can mistake this lymphocytosis for treatment failure, so understanding the lymphatic dynamics is genuinely important for interpreting the response.

CAR T-cell therapy, which engineers a patient’s own T cells to target leukemia, has produced remarkable results in B-cell acute lymphoblastic leukemia, with complete responses in the majority of treated patients. The therapy has been less successful against lymphomas, and the distinction likely has to do with the lymphatic system itself: solid masses of cancer within lymph nodes create physical barriers and an immunosuppressive local environment that make it harder for CAR T cells to penetrate and function effectively compared to leukemia cells circulating freely in the blood and marrow.¹⁷

The Role of Vascular Remodeling

Leukemia does not just passively occupy lymphatic and lymph node territory. It actively remodels the local blood vessel network to support its own growth. Leukemia cells produce proangiogenic and inflammatory signals, including basic fibroblast growth factor and interleukin-1, which stimulate nearby endothelial cells (the cells lining blood vessels) to release vascular endothelial growth factor C, or VEGF-C. This molecule then loops back to act on the leukemia cells themselves through a receptor called FLT-4. The interaction promotes leukemia cell proliferation, boosts survival by shifting the balance of internal cell-death regulators, and even protects leukemia cells from the killing effects of chemotherapy drugs.¹⁸

VEGF-C is best known for its role in lymphangiogenesis, the growth of new lymphatic vessels. The fact that leukemia cells co-opt this pathway raises the possibility that they are not just hiding in existing lymphatic structures but actively encouraging the growth and remodeling of lymphatic and vascular networks in their vicinity. This vascular remodeling is one reason why disrupting the leukemia-microenvironment crosstalk, rather than targeting the leukemia cells alone, has become an active area of drug development. Drugs that block these signaling loops could theoretically make leukemia cells more vulnerable to chemotherapy by stripping away the protective niche the tumor has built for itself.