How Cancer Can Cause Low Blood Pressure

Cancer can lower blood pressure through at least half a dozen distinct mechanisms, from tumors physically invading hormone-producing glands to the immune system’s own inflammatory overreaction during treatment. In one study comparing hospitalized cancer patients with non-cancer patients, those with active cancer were about twice as likely to have orthostatic hypotension, the kind of blood-pressure drop that hits when you stand up. The routes connecting a malignancy to a falling blood-pressure reading are varied enough that clinicians sometimes discover the cancer only after investigating unexplained low blood pressure.

How Common Is the Problem

Low blood pressure in cancer is underappreciated partly because high blood pressure gets most of the attention. A 2024 study of over 400 patients found orthostatic hypotension in about 29 percent of those with active cancer, compared with roughly 17 percent of patients without cancer. In that same analysis, cancer status was the strongest independent predictor of orthostatic hypotension after adjusting for other factors like age and medication use. Lung cancer stood out, with nearly 58 percent of lung cancer patients meeting the threshold, followed by breast cancer at about 38 percent and head-and-neck cancers at around 31 percent.¹

Those numbers reflect orthostatic hypotension specifically, meaning a measurable drop when changing position. The broader picture of low blood pressure in cancer also includes sustained hypotension from organ damage, acute crashes during sepsis, and treatment-related episodes. Each pathway has different timing, severity, and implications for care.

When Tumors Invade the Adrenal Glands

Your two adrenal glands sit on top of the kidneys and produce cortisol and aldosterone, hormones that help maintain blood pressure by regulating fluid balance and vascular tone. When cancer spreads to both adrenal glands and destroys enough tissue, the resulting hormone deficit can cause blood pressure to plummet. This is called primary adrenal insufficiency, and it produces a cluster of symptoms: fatigue, nausea, weight loss, and hypotension that can be severe enough to look like septic shock.

A systematic review of bilateral adrenal metastases found that hypotension was present in about 69 percent of those cases.² Lung cancer is one of the more common culprits. In one reported case, a lung cancer patient with metastatic adrenal insufficiency began hormone replacement with hydrocortisone and fludrocortisone, and his blood pressure normalized within days.³ Breast cancer can follow the same pattern. A breast cancer patient whose persistent nausea and vomiting were initially attributed to other causes turned out to have bilateral adrenal metastases; replacing the missing hormones resolved her symptoms completely.⁴

The treatable nature of this problem is what makes it important to catch. If doctors assume the low blood pressure is just a general consequence of advanced cancer and do not check adrenal function, the patient misses out on a straightforward hormonal fix that can dramatically improve quality of life.

Tumors That Secrete Vasoactive Substances

Some cancers actively manufacture chemicals that dilate blood vessels or otherwise push blood pressure down. Neuroendocrine tumors are the classic example. Carcinoid tumors can release serotonin, prostaglandins, histamine, and other vasoactive compounds directly into the bloodstream. The result, known as carcinoid syndrome, typically includes flushing, diarrhea, and hypotension. This usually happens when the tumor has spread to the liver or when it sits in a location like the bronchi where its secretions bypass the liver’s usual filtering.⁵

A rarer variant is the VIPoma, a pancreatic tumor that pumps out vasoactive intestinal polypeptide. One documented case showed watery diarrhea, dangerously low potassium, and sustained low blood pressure with visible skin flushing, all driven by persistently elevated VIP levels.⁶ These tumors are uncommon, but their blood-pressure effects can be the presenting symptom that leads to the cancer diagnosis in the first place.

Fluid Around the Heart

Cancer can cause fluid to accumulate in the pericardium, the sac surrounding the heart. When enough fluid builds up, it compresses the heart and prevents it from filling properly, a condition called cardiac tamponade. The result is a rapid drop in blood pressure that can be life-threatening. Cancer accounts for roughly one third of all cardiac tamponades, making malignancy one of the leading causes of this emergency.⁷

Lung cancer, breast cancer, lymphoma, and melanoma are among the types most associated with malignant pericardial effusions. The diagnosis is often incidental, caught on imaging done for another reason, but when it progresses to tamponade the blood-pressure collapse can be sudden. Draining the fluid, usually through a needle procedure called pericardiocentesis, restores cardiac function and brings blood pressure back up. The key clinical challenge is recognizing the effusion before it causes hemodynamic collapse, because the symptoms can mimic other problems common in cancer patients, like shortness of breath and fatigue.

The Nervous System Under Attack

Blood pressure regulation depends on a functioning autonomic nervous system, and cancer can disrupt that system in ways that are easy to miss. One route is paraneoplastic syndrome, where the immune system produces antibodies against cancer cells that also attack nerve tissue. A case involving small cell lung cancer demonstrated orthostatic hypotension as the sole neurological feature of a paraneoplastic autonomic neuropathy triggered by a specific antibody.⁸ The cancer itself may be small or even undetectable at the time the neurological symptoms appear, which is one reason these cases are diagnostically tricky.

Cancer treatment can also damage the blood-pressure control circuitry. Radiation to the neck, used for head-and-neck cancers and some lymphomas, can injure the carotid sinus baroreceptors, which are the sensors that detect blood-pressure changes and signal the brain to adjust accordingly. When those sensors fail, the body loses its ability to stabilize blood pressure in real time. Researchers described patients who developed wildly swinging blood pressure and chronic orthostatic intolerance years after neck irradiation. The proposed mechanism is that radiation accelerates hardening of the carotid arteries, locking the baroreceptors in place so they can no longer detect pressure changes.⁹ This is especially insidious because the delay between treatment and symptom onset can be years, by which point neither the patient nor their doctor may connect the two.

Infections and Sepsis

Cancer and its treatments frequently suppress the immune system, and the resulting vulnerability to infection is one of the most common causes of acute low blood pressure in cancer patients. Chemotherapy often reduces neutrophils, the white blood cells that form the front line against bacterial infections. When a neutropenic patient develops a bloodstream infection, the inflammatory cascade can rapidly progress to septic shock, characterized by a severe drop in blood pressure that resists fluid replacement.

In one study of febrile episodes in neutropenic cancer patients, about 13 percent of episodes progressed to septic shock, with roughly half of those patients dying.¹⁰ This is why oncology teams treat fever in a neutropenic patient as an emergency. The window between a rising temperature and a crashing blood pressure can be narrow, and early antibiotics are the most effective intervention. Any cancer patient who has recently received chemotherapy and develops a fever with lightheadedness or confusion should seek immediate medical attention.

Chemotherapy and the Heart

Beyond immunosuppression, chemotherapy can directly damage the heart muscle. Certain drug classes are well known for cardiotoxicity, and the resulting weakened heart may not pump forcefully enough to maintain normal blood pressure. The range of cardiac complications linked to chemotherapy includes arrhythmias, inflammation of the heart muscle or its lining, and frank heart failure.¹¹

Anthracyclines, a class of drugs used against breast cancer, lymphoma, and leukemia, are the most notorious offenders. The damage is often dose-dependent and can be cumulative, meaning it may not show up until months or years after treatment ends. Other agents, including certain targeted therapies, can cause more immediate drops in blood pressure during or shortly after infusion. Cancer patients on active chemotherapy are typically monitored with periodic cardiac imaging, but mild blood-pressure changes can slip through if they develop gradually.

Cytokine Release Syndrome During Immunotherapy

Newer cancer treatments have introduced a newer cause of low blood pressure. CAR T-cell therapy, which engineers a patient’s own immune cells to attack cancer, can trigger a massive inflammatory response called cytokine release syndrome. This reaction is driven by a flood of inflammatory signaling molecules and is characterized by fever, low blood pressure, and breathing difficulty.¹² It is the most common serious side effect of CAR T-cell treatment.¹³

The low blood pressure in cytokine release syndrome is primarily caused by widespread blood vessel dilation and fluid leaking from capillaries. Patients may respond only briefly to intravenous fluids, requiring medications that constrict blood vessels to maintain adequate pressure.¹⁴ The severity can range from mild, self-limiting episodes to ICU-level emergencies. Blocking the inflammatory cascade with drugs that target specific cytokines, particularly interleukin-6, has become a standard part of managing severe cases. As immunotherapy use expands, this category of treatment-related hypotension is becoming more visible in clinical practice.

Amyloidosis and Blood Pressure Regulation

Some blood cancers produce abnormal proteins that deposit in organs and interfere with their function. In light-chain amyloidosis, a condition linked to certain plasma cell cancers, these deposits can infiltrate the heart and the autonomic nerves. Both effects conspire against blood-pressure control: a stiffened, infiltrated heart cannot pump effectively, and damaged autonomic nerves cannot signal blood vessels to constrict when needed. A study examining the cold pressor test in light-chain amyloidosis patients found that abnormal blood-pressure responses during the test were associated with both neurological dysfunction and cardiac infiltration, and provided prognostic value beyond standard staging.¹⁵

This dual-hit pattern makes amyloidosis a particularly difficult cause of hypotension to manage. Treating the underlying cancer to stop production of the abnormal proteins is the long-term goal, but blood-pressure support often requires careful balancing of fluids, compression garments, and medications that may themselves stress an already weakened heart.

When Low Blood Pressure Is the First Clue

One of the more unsettling aspects of cancer-related hypotension is that it sometimes precedes the cancer diagnosis. The paraneoplastic neuropathies mentioned earlier can produce orthostatic symptoms months before the underlying tumor is found. Adrenal insufficiency from metastases can mimic other conditions for weeks or months. VIPomas and carcinoid tumors may present initially as unexplained flushing and diarrhea with low blood pressure, sending patients through a series of gastroenterological evaluations before anyone thinks to check for a neuroendocrine tumor.

For doctors evaluating otherwise unexplained, persistent low blood pressure, especially when it comes with other red flags like unexplained weight loss, new fatigue, or abnormal electrolytes, cancer belongs somewhere on the differential diagnosis. This is not to alarm anyone whose blood pressure runs low; most hypotension has benign causes. But the connection between malignancy and blood-pressure drops involves enough distinct pathways that it warrants clinical awareness, particularly in older adults or people with risk factors for cancer.

Dehydration, Malnutrition, and the Compounding Factors

Many of the mechanisms above operate on top of a baseline that already tilts toward low blood pressure. Cancer patients frequently eat and drink less due to nausea, pain, or treatment side effects. Persistent vomiting or diarrhea, whether from the cancer itself or from chemotherapy, depletes the fluid volume needed to maintain pressure. Cachexia, the muscle and fat wasting that accompanies advanced cancers, reduces the body’s overall vascular tone. Opioid pain medications, which are common in cancer care, can lower blood pressure by dilating blood vessels and reducing sympathetic nervous system activity.

These contributing factors mean that a cancer patient often does not need a single dramatic insult to develop hypotension. Instead, several moderate insults stack up: a mild reduction in fluid intake, a moderately weakened heart, slightly impaired autonomic function, and a medication that lowers vascular tone. Each alone might be tolerable, but in combination they push blood pressure below the threshold where the patient feels dizzy on standing, cannot tolerate activity, or risks falls. Clinicians managing cancer patients generally keep all of these contributors in view simultaneously rather than searching for one single explanation.